Did Liars and Thieves Misdiagnose this Car or Am I the Bad Guy

[@billnelson269]

I've owned a shop for 15 years. You are spot on. We operate with old school morals and ethics. I turn away roughly 20 people per day. And my customers won't go anywhere else. Honesty is easy and WILL make the money flow.

[@SchrodingersBox]

Bravo!!!!!!

[@pamelavance648]

Location please

[@SchrodingersBox]

Denver Colorado

[@windward2818]

Since you own a shop maybe you could answer this general question. If a shop does not do diagnostics up front how can they accurately provide a repair estimate? If you don't know what's wrong, how do you know what to repair?

[@SchrodingersBox]

Great question. I can’t speak for people who own a shop but I do happen to know in communicating with actual techs that shops that don’t do actual diagnostics they typically use AllData and they use the frequency of repairs feature to look at the most common cause of the issue and assume it to be the fix. They build the quote off that.

[@rplayer9969]

Well Matt, I've left you a few comments before. I'm almost 73 now. I have 2 hobbies, watching your videos and bowling. 25 - 300's. Looks like I'm gonna sign up to your channel. Tell me how to enlist. You are the GREATEST. And yes. I yelled " GREATEST " !!!

[@SchrodingersBox]

Hahah thanks so much. By the way I worked at a bowling alley when I was 15. Was there for 13 years. Never bowled a 300. 279 is my best. I never seen anyone bowl 25 300’s but I remember watching a guy bowl a 898 series.

[@sheerwillsurvival2064]

He’s back !!

[@carlm2590]

God bless you for not charging them, and the good video

[@r.weaver3769]

Matt, I agree, when I was working as a tech, my philosophy was always "If you pay more attention to helping the customer than what it pays, your paycheck will take care of itself". My goals were always fixing the car right or leaving it in the same condition it was when it rolled out of the factory.

[@SchrodingersBox]

How funny because I have used a nearly identical version of that with my clients for my real job. “If you take care of your clients, they take care of your numbers”. It’s a great philosophy! Glad to see someone else who owns it too!!

[@charlesgould8436]

I think of the car, not who's driving. I think of drivers driving home:)

[@MrCountmein3]

Yes a honest person with a conscience. Great job. You make Great videos. You have a wealth of knowledge that you share with us. Thank you.

[@SchrodingersBox]

thanks for the nice comment!

[@mph5896]

Well, compression test you get a very brief blast of air/pressure on the leaky section of the gasket. Leak down test is a consistent pressure being held on a weak gasket.

[@joejones711]

Love how you’re precise and the fact you’re not trying to mess people over. VERY SMART MAN

[@Eddiegrant69]

If you put a pulse sensor or a pressure transducer connected to your pico into the coolant neck, you might see a small pressure increase when the bad cylinder is on compression. This should work because you had pressure in there after cranking when you took the cap off. If there is a misfire, you can put them in the exhaust aswell. This would be very helpful to pinpoint which cylinder to test if there was no misfire data.

[@SchrodingersBox]

great recommendation!!!

[@John76546-x]

You got here first. This should pick up the pressure pulses going into the cooling system. Might be more accurate with a pulse sensor.

[@bleebleblahble8833]

Please do a follow up if possible. Would be great to see.

[@NZdiagnostics]

Came here to say this too! Sync it with a coil or fuel injector and you can locate the exact problem cylinder. It works with either a regular transducer or a first look type pulse sensor. Super quick, accurate and easy.

[@SEXYTECH1000]

@@NZdiagnostics GREAT ADVICE , BUT ALWAYS SINC TO THE COIL NOT THE INJECTOR , INJECTOR FIRE BEFORE AND AFTER INTAKE VALVE OPENS AND CLOSES SO IT'S NOT TRUE TDC. THE COIL TIMING WILL BE MORE ACCURATE.

[@carguy1312]

Rest assured you didn’t steel the customer, the other shops all but forced them to you. You’re such an inspiration to all of us. Thank you for talking through the thought process of being a good human.

[@SchrodingersBox]

Good way of looking at it!!

[@foreverwood1963]

Thank you for saying what you said about crooks. I keep asking when did it become ok for people to cheat us? When ? It’s fraud and should be dealt with like fraud. I keep saying the same with buying certain things on Amazon. How can it be ok for so many buyers to say it didn’t work at all whatever they bought? Thank you for having the heart and compassion to not hit this customer harder when you actually did the work.

[@williamburdon6993]

I think you did a great job, and I hope this person becomes a great customer for you in the future. I feel like you do, treat people honestly, you will sleep much better at night. My wife gets so angry with me because at 73 with a bad back and shoulders I do everything myself, I told her "I would love to pay someone competent a great wage to fix things for me , but every time I do that, they do not do the job correctly, or they skip steps for a few dollars and it looks crappy or only lasts a short time.

[@ulfg1409]

A few suggestions: For the voltage relative compression test, set the channel to AC coupling, reduce voltage to something more like +/-2V, whatever is suitable. Should make the variations far more obvious. For the amp clamp relative compression test, use filtering to remove most of that noise. Noise can hide lots of details. Again, AC coupling may also improve the situation, or not - try it and see. For additional tests, try a pressure pulse sensor or pressure transducer connected to the cooling system. You should see when the cooling system pressure increases = when one cylinder leaks into the cooling system. Add a sync signal from #1 ignition for example and you'll see which cylinder is leaking.

[@mikeberesford4955]

Are those sensors that sensitive? I see your point like an adaptive radiator cap ,so it would show pulse with leaky cylinder. That would be SO much easier!

[@ulfg1409]

@@mikeberesford4955 They can be. Probably nog sensitive enough for every time, but often enough to be worth checking.

[@smiles7631]

I have worked at a couple shops over the years and it doesn't suprise me that they look over the whole car. I remember the franchise would make us fill out these forms for every car that came in. I would feel sorry for the customer that just wanted an oil change and got a qoute for 1000 worth of work. Anyways, I just do this to help people out and make a little extra money now. I love watching these videos and learning about all the new tools that come out. I just bought an inspection camera from the big A for 100 and I was floored by how clear the video is and it has a side view camera. I would bet that if you pulled the spark plugs and looked in the cylinder with this camera you could see the staem cleaned piston right away. Thank you for the video!

[@SchrodingersBox]

Great comment. Yes it is hilarious to me when I see these write ups for thousands of dollars when the customer wants new tires or whatever. Sheeesh lol. Yeah I totally which I borescoped the cylinder. Also the presence of enough coolant in the cylinder probably made it so it couldn’t be squeezed out and thus the compression didn’t lower.

[@r.weaver3769]

I too have worked at shops that require those forms. One shop owner said, "If theres iron on the rack theres money to be made" Didn't take long to leave that one.

[@charlesgould8436]

When I bring my vehicle to someone for diagnosis it is nice to know everything!:)))

[@mikebaz7843]

Sometimes you can't win. If you quote roadworthy items to prevent "since you worked on my car.." they don't like it, but if you don't quote oil leaks and bald tyres, they get upset too

[@edwardturello2782]

Awesome video Matt, glad you're back. I always thought that a cylinder pressure test was the answer for compression problems but I stand corrected so thanks again for PROVING it on video and pointing out a better way to diagnose that type of problem. I don't mind putting in the work if the results are correct and by the way I share your views on the current declining status of our American values

[@SchrodingersBox]

So glad to hear - on all counts!!! Yeah I don’t mind admitting I am wrong and my reliance on compression tests earlier on was indeed an oversight. It can be misleading.

[@abderrahimmark]

I am just like José, I mean learning out of passion form guys like you and Scannerdanner. I learnt alot. There is many of us, Josés, out there appreciating your work. Thank you.

[@SchrodingersBox]

I am very aware of that!!! In fact I make this channel EXACTLY for you guys!!! You are the target audience I have always aimed for.

[@abderrahimmark]

@@SchrodingersBox WE LOVE YOU! 🙌🏻

[@SchrodingersBox]

Hahaha love you all too!!! I really do!!

[@ourkid2000]

Great video Matt! Flat rate master did a pretty cool video about head gasket testing and he mentioned an interesting method of pressurizing the cooling system and looking in the cylinder with one of those endoscopes for the appearance of wetness on top of the pistons......thought that was a pretty neat idea.

[@BblastedD]

Matt dropping some red pills in this one. Thieves = admired. Honest = suspicion.

[@rmr5740]

That's how you achieve "equity".

[@robertmedina6875]

You are very sharp!! I am retired …. and I have work every day in a shop diag. cars. It looked like a small leak in the wave form Big Matt! Great video!!!!

[@northernpatriot9078]

Hey thank you sir I bought xtool it helped me fix a friend's misfire and transfer case encoder motor fix thank you sir 😊!! Fuel trims look 👍

[@SchrodingersBox]

great to hear!!!

[@chriscooper2454]

BTW, you're the greatest chemist/engineer/mechanic I've seen, hands down

[@SchrodingersBox]

much appreciated lol!

[@rolandorosales5530]

Hey Matt! What I’ve done in the past is install a coolant pressure tester (cold engine) and leave it (with no pressure) while I crank the engine over just like a relative compression test and if it creates pressure it pretty much guarantees a bad head gasket

[@SchrodingersBox]

Yes I have heard of that too!!

[@rolandorosales5530]

@@SchrodingersBox another thing that I have learned from Eric O. (South Main Auto) and super Mario diagnostics is to install a pulse sensor like the first look in the cooling system and sync it with the relative compression test and and ignition event. You are going to see small bumps on the cylinder/s that may have the leak instead of doing a leak down test on all the cylinders. Personally I have only seen a couple of times since I learned about the test.

[@rolandorosales5530]

Didn’t realize you were making a video about this very test 😅

[@SchrodingersBox]

Hahahaha yes I just did it. Video coming out soon!!

[@JrSpitty]

There is a better way, but only on cars that support individual cylinder misfire data. You will get a misfire on that cylinder on cold start, most newer cars have a misfire counter for each individual cylinder and that will help point you where you should be doing a leakdown on. If there is no "misfire" data, some vehicles tell you the speed variation of the crankshaft per each cylinder you can go off of that. But older cars you simply won't get that data as it isn't programmed in to tell you what cylinder is misfiring. Relative compression like you said is sometimes fruitless, because a head gasket leaking into a coolant jacket usually doesn't cause a significant loss of compression, its simply coolant being sucked in on the intake stroke. Your P0307 is basically your pointer already. But sometimes its nice to verify misfire in live data via the counter. Because it won't always trip the code.

[@SchrodingersBox]

Good advice. I am actually aware of this but haven’t introduced concept in videos yet. Maybe time to do that.

[@Jason-cu1jp]

Completely agree re. the other shops. None of the other crap matters until they've addressed the elephant in the room. Your poor customer would have thrown all that money away and then still be met with the cost of a head gasket repair. Also, for your chef friend, can recommend the HoldPeak 600amp AC/DC current clamp. It's the cheapest one I've found that works perfectly for relative compression tests. Thanks for the video.

[@jgeorges3061]

MATT, you rock brother as always by sharing ur approach and information with ur viewers and those days most of they call them professional garages are most of the time part changers I work in dealership and most of the time i see part changers not real technicians and most of the time charges the customers for things they do not need what else can i say this is the real world we living in. cheeeeeers

[@SchrodingersBox]

Thanks my friend!

[@TriggerTravels]

I used to work for Caterpillar global engine development testing engines. We used in cylinder pressure transducers to monitor cylinder pressure while the engine was running. We did this to monitor knock while advancing timing. Anyways... The pressure developed during combustion is much higher than that developed by just cranking the engine. If the head gasket is minimally compromised it may not show on a simple compression test. Cylinder pressure during combusting will be much higher and be enough higher that it produces the symptoms of a blown HG. I've seen this on diesel engines several times. All the symptoms of a blown HG... Compression test normal. This is even more disturbing since diesel engines typically make in excess of 400psi during normal cranking. I've seen several diesel engines with blown HG run mostly normally and never over heat either. The only real indication is excess pressure in the cooling system. Good video 👍

[@mikeberesford4955]

Good point ,wasn't even thinking about that.

[@windward2818]

Good point except a test was done with compressed air to about 75 psi and there was air escaping at the open radiator cap. The gasket is clearly compromise at much lower pressures than average combustion pressure.

[@JeffreySchaller-t1e]

I just replaced the heads because the comp was horrible turned out it was the valve stem seals. Love your channel thx. Mat.

[@jeffjohns2189]

Great information, just a guess this has an iron block with aluminum heads and uses a multi layer steel shim type of head gasket. They do this to allow for some movement between different expansion rates of the two types of metal. Gasket may not be blown just leaking, I've had the same symptoms and replaced the gaskets not being able to actually find the spot where it had failed. I always wondered if it would help to just re-torque the head bolts.

[@rwrobs777]

Matt, Great video !!…instead of using 20 volts DC for the RC test use “AC Coupling”…change the DC to AC and select a 1 volt scale…the compression peaks will be on the bottom and not at the top as you would see with the AMP clamp setup…have you used the WPS on a radiator for a blown head gasket ?? C5 Diag

[@SchrodingersBox]

Thanks Robert - yes others pointed out the radiator pressure. great idea. I hope with the coolant it won’t damage the WPS- will it??

[@markchidester6239]

IMHO, It may be possible the other shop pointed out the other issues to give the customer an ability to make an informed decision on the investment needed into the vehicle. I would imagine if they didn't know all of this information, they would have asked you to do the head gaskets rather than cut their losses. Excellent video! Your line of thinking is fantastic and i completely agree with the "Bad Guy" outlook. The investment outlook is for people who wish to succeed. Absolutely solid advise! Your a good man Matt!

[@JohnDoesGarage]

We are both on the same soapbox. I would love to go fishing with you so we could commiserate on just how despicably pathetic society has become. If I have learned anything in my over forty years of spinning wrenches, it is there are no absolutes in this profession. You will eventually run across a vehicle that will make a liar out of you. It's just part of the gig. Great video as usual.

[@SchrodingersBox]

Thanks my friend. If you ever find yourself in Denver let me know!! Lots of fishing here!!

[@JohnDoesGarage]

@@SchrodingersBox I’ll certainly do it.

[@Netherlands031]

About the test 'lying' - seems to me that if you have a small leak, then that won't show up on the compression test but it can be big enough to let coolant into the cylinder and cause problems there. You only need a few drops of coolant every engine rotation for a big problem, but a few drops of air missing from the compression, you won't notice. Also, applying a denoising (lowpass) filter to the starter waveforms might help a lot, they're so fuzzy now you can't see much.

[@billyfox384]

I generally don't use compression for a suspected head gasket issue, for the very reasons your showing. The block test is the most accurate. If there are hydrocarbons in the coolant it has a blown head gasket. At times coolant (under pressure) is being forced into the cylinder, which would not be a loss of compression, At other times exhaust is being forced into the coolant system, which you proved with the air in the cylinder. Not sure why but this seems to not effect compression as well, or affects it to such a small degree. Anyway like your channel you do a great job. At my shop we always perform a block test on any car that has overheated b4 doing any repairs. There are times when that is simply not possible do to how severe the leak is.

[@atlantasamedaydelivery1769]

Also, Matt, we appreciate your honesty and skill. The society has propped up theieves and conmen in media and music. We need more men of honor to thwart this trend. Be well Matt

[@SchrodingersBox]

Thank you!!

[@everardocamacho5063]

Great video matt as usual, cheers from ontario ca.

[@donkaiser6704]

Was the "clean" looking plug from #7 (the cylinder with reported misfire)? If so, might have been steam-cleaning due to the head gasket failure into the coolant passages.... Might have been interesting to see what the top of the piston looked like, as well. Great video, thanks!

[@SchrodingersBox]

Yes but it also was could be clean looking because it only was replaced 3 weeks before while the others were in there 5 years.

[@mikemuzzell5167]

Car overheats I’m doing a oil changes right away. Good to see you against sir. I did in fact buy the d7 on your recommendation and I’m super happy with it so far. I’m a heavy truck guy and have my fair share of pick ups to work on. This tool makes a lot of diag possible. D7 for the money is the best.

[@SchrodingersBox]

Great to hear!!!

[@MrOctNot]

Could it be that compression leaks into coolant system don't show in relative compression waveform because "you can't compress a liquid"? Perhaps it should be standard practice to remove the radiator cap when performing relative compression tests. Perhaps even removal of the oil filler cap and a major vacuum line (e.g. brake booster hose).

[@SchrodingersBox]

I absolutely agree that is the best explanation.

[@randyrobison335]

Thanks for sharing. My guess is that the hydrostatic pressure of the coolant is giving you good compression.

[@mtrltoolman]

Hi Matt, good to see you again!!

[@SchrodingersBox]

Yay! My friend is back!!! Always good to see you!!!

[@advancedleveldiagnostics]

Great job Matt, Thanks! Another way the RC test can "Lie" is with a valve issue, that's why It is better to do an RC test with a pulse sensor in the intake. I don't think it would help you in this case unless you put one in the radiator neck as well.

[@SchrodingersBox]

Agreed! Will do that next time for sure.

[@TMccrury]

Great video. I learned a lot. Regarding the "Faulty" compression test from voltage as well as the gauge direct to the cylinder, is it possible that the hole in the head gasket is just small enough that it will hold pressure for the gauge and the Pico but when positive pressure is applied from the leak down test opened it and kept it open. My dad had a head gasket blow on a 80 something model Pontiac and it was pouring smoke. This appeared to be a small amount of smoke. Either way, head gasket blown.

[@LyallBates-xn4jd]

Hi Matt, full radiator, cap off crank engine and look for the bubbles, no tools needed..

[@SchrodingersBox]

the water pump itself often causes bubbles though. I have tried that many times and it’s inconsistent. also- even if it was a cylinder leak- how would I know WHICH cylinder it is?

[@LyallBates-xn4jd]

@@SchrodingersBox Hi Matt, fair comment, but there's a difference between the more consistent small bubbles of a water pump leak and the surge of an compression leak whether it is from a porous cylinder, cracked head or blown head gasket.The point I was making is that you can use this to get a fair idea of the problem on the side of the road away from home or service centre. As for which cylinder it is you could try leaving the spark plug out of each cylinder in turn and see if there's a reduction in pressure in one or more (adjacent) cylinders.

[@SchrodingersBox]

Well wait-- if you have to remove the spark plug to do that, why not just do a leakdown test to bring with? Also what if the cylinders are under the intake manifold? And also what if the compression loss isn’t to the cooling system- how would that be determined- you wouldn’t know with this test. A method is needed where you can identify all cylinder leaks and identify the affected cylinder without removing spark plugs.

[@Darkshadow10157]

Love the video! Very informative and definitely something I'll remember. There's one thing I'm confused about, though. At the end of the video, you were looking for a reliable head gasket test that doesn't require going to each cylinder since that's difficult to do on some vehicles. Clearly, the RC test isn't the answer, but what about the chemical test? Doesn't the fact that the chemical test showed the presence of hydrocarbons in the cooling system definitively prove head gasket failure (or cracked block)? Or is the issue with it the fact that it would not show compression issues due to anything other than a head gasket failure? I'm curious if the RC test lies for other compression issues as well. Maybe those 2 tests together would give you the most reliable, non-intrusive diagnosis.

[@SchrodingersBox]

The RC test is quite reliable however the issue I have with it is that it only works if the compression loss is to the cooling system. If the compression loss is anywhere else it will show negative.

[@wheelersgarage8393]

Matt. The reason the compression test lied is the water can not get out of the way fast enough. Cheers Adam

[@SchrodingersBox]

Oooohhhhh!!! that’s a good thought!!

[@brownwrench]

Not blown out big enough

[@wheelersgarage8393]

Yes true and is a factor. Water can't be compressed. If there was no water in the system, you should see a difference in the maximum compression reached. The difference may only be very slight, depending on the size of the blow out though.

[@atlantasamedaydelivery1769]

The chemical test is awesome. I have to procure that tool or kit for head gasket diagnostics.

[@SchrodingersBox]

One of my favorites!’

[@atlantasamedaydelivery1769]

Matt sir, if I may ask, do you have a particular company that you prefer to use dye to determine if carbon dioxide is in the coolant.

[@lance1097]

You can scope the radiator with a pressure transducer.

[@SchrodingersBox]

oh damn that’s a great idea. dammit I wish I had thought of that. of course this would only work if the compromise was to the cooling system but it’s better than what I did!

[@chrisi1909]

@@SchrodingersBox And you could Sync it with spark or Injector or flywheel trigger and see what Cylinder is pushing the Coolant without removeing a Sparkplug for Testing

[@SchrodingersBox]

Totally agree!!

[@williamwhite9767]

Back around 2000, I was a victim of failed head gasket diagnosis I think. I had bought my daughter a 92 Pontiac Sunbird. It had overheating problems and the local chevy dealer kept replacing stuff such as fan switch and radiator without diagnosing the real problem. She was away at school and it ran hot while she was somewhere she didn't want to stop and really overheated it. I drove there 6 hours away and the car failed to start. So, thinking it probably needed an engine and possibly a transmission, I called a local salvage yard and sold it to them for $250. On the way back to her apartment I stopped at a Ford Dealer and bought her a 99 Ford Contour with 23k miles on it. It lasted her to 170k miles with questionable maintenance. That chevy dealer has terrible mechanics based on that experience and others, just parts changers.

[@rodneygarcia7858]

i joined ur community because i find ur videos very helpful. Especially right now that ive been struggling to get my Chevy Cobalt 2.4 running again. Right now i hit a wall and got a no start with no codes. can u point me in the right direction in ur videos to see if my coil packs r throwing spark

[@SchrodingersBox]

You will want to start with my FASTTEC video. It always finds the issue every time.

[@joshuahippe]

Excellent video! Would a pressure transducer with the Pico shown an issue?

[@SchrodingersBox]

yes it would- I believe I show that in next video.

[@alexismarcyting5340]

hey Doctor Matt, it is more accurate when you test the compression together with the intake pulse.

[@LitoVeloria]

The words "Never" and "Always" are 2 of the most abused words in our vocabulary so I'm very careful in the ways I use them. Compression tests never lie. Faulty equipment and/or misuse usually lie. Engine Compression isn't always affected by head gasket issues. It all depends on what part of the head gasket is damaged. It could be damaged at one of the coolant ports and have nothing to do with Compression or cylinder head could be cracked on an area of a coolant port that is not adjacent to the combustion chamber. Most components have several different tests. Therfore just because it passes one test doesn't always mean it's a good component. The only way to pinpoint and verify is to do all the necessary tests. Hey, thankyou for sharing your vast array of knowledge with us while saving us a great deal of headaches and money as well as discovering fascination of figuring out how things work. Your intelligence, modesty, and honesty are an inspiration to me and I'm glad you do what you do. I don't believe that money makes the world go round like they say. I think it makes some people dizzy going around in circles being busy.

[@jonwillfixit]

Good work! FYI do the chemical test outside, It will pickup hydrocarbons in a garage & give you a false reading, it’s happened to me

[@Leesherwood]

Knowledge is Power

[@simonilett998]

Matt, it is very common for a cylinder that has coolant ingress not to show low compression if the leak hasn't gone in long enough to cause cylinder damage. Also, any coolant that gets into the cylinder may actually help to seal up a small leak. Any liquid in the cylinder potentially could even reduce the cylinder volume enough to balnce any existing compression loss due to any damage that may be present, or present a partial hydo lock effect, essentially increasing amperage seen on an RCT and show up as a balance with other cylinders...mind you I'm just speculating and thinking outside the boxwrench here..lol😁 The leak may be small enough to allow combustion gasses into the cooling system, but since each compression stroke happens so quickly there's very little time for it to be visible on any kind of compression test. With the leakdown test, you are doing it with the piston in a static position, over a much longer time period comparatively. One way that may work to pinpoint a compression leak into the cooling system, and at the same time identify the problem cylinder, is to put a pressure transducer on the radiator neck or coolant header tank, and also connect a 2nd channel to one of the cylinders as a sync, ie. an ignition coil etc. You should be able to see the pressure pulses at the cooling system and identify the problem cylinder by using the firing order and cylinder sync. I'm pretty sure you already know this, or since you're a bit of a thinker you will most likley think of it anyway, perhaps it just simply slipped your mind in this video🤣🤣👍🇦🇺

[@SchrodingersBox]

Correct on everything. We are going to test these concepts in next video.

[@ayayron10]

Nice video. I have grown to appreciate mechanics work, even more than before, and learned a few things in regard to my car watching these videos. I was curious do you usually have to rev the gas pedal in order to get the whitw smoke to come out the tail pipe from a cold start or not typically? Also curious why a false positive result could happen with a leak down or compression test? Is it the size of the leak or location of the leak? Could you also get a flase positive on a chem test if the leak is small or very small? I was told if it is super small it may not show up until the leaking area grows. So if that case is the collant level in the reservoir, the only way to tell until it gets as bad as this car did?

[@SchrodingersBox]

Yes it’s a lot more technical than people think!! You won’t get a false positive on a leakdown test (unless you do it wrong) but you can get a false negative. Often this occurs if the leak is in the cylinder but below the piston at TDC. It also can happen if the leakdown isn’t applied long enough. A false positive on the chemical test is also not likely if it’s done right but a false negative can happen if the combustion leak isn’t to the cooling system.

[@ayayron10]

@@SchrodingersBox this makes sense then. So it's more of where the leak is not the size of the leak. And when you say how long the leak down test is done, so if say a mechanic did a quick leak down the car could possible pass the test but still have a problem? And do you usually have to rev engine in order to get the white smoke, or if it's in idle for maybe 5 minutes would you still see little puffs from tail pipe if sa6 the leak is minor or small?

[@ayayron10]

​​@@SchrodingersBox I also got my terminology incorrect I mean you would get a flase negative ie pass a test but really you could have an issue. My mistake. Wish I could bring my car in to a guy like you. I think I may found a good shop in my town but like these customers of yours I feel I have gone to some so so places which makes it hard to trust, granted like you pointed out sometimes the test "lies". It's good, though, like a scientist, ypu do test more than once.

[@MarzNet256]

I wonder if the head warped from an overheat event(s) and yet somehow is less warped when it's at operating temperature vs when cold-and/or expanding metal seals the gap. It seems somewhat counter intuitive, but I"m guessing that warpage, especially after several cycles with different rates of overheating and cooling, is a complex process. However, under higher engine loads the head gasket leaks more at any temperature (white smoke). Also, I know it's crazy, but could coolant somehow be getting into cylinders via the intake?

[@gregwhite5058]

Matt, not sure whether you'll see this since this video was put up about a month ago. Regarding failure of the fluid test for blown head gasket, Eric O. just did a video where he talked about needing to rev the engine pretty high while doing that test to blow out accumulated air before exhaust gases can make it to the fluid. In his video the fluid stayed blue for a long time until he revved the engine several times, eventually turning the fluid yellow. Thought you might like to know this for future reference.

[@SchrodingersBox]

I see it and yes I agree it’s a good advice.

[@anonintellect9882]

Was compression test done with rad cap off?? Was compression/ pressure being held in cooling system giving false cylinder pressure reading?

[@SchrodingersBox]

Good question. Rad cap was on.

[@anonintellect9882]

@@SchrodingersBox cooling system could have been buffering/maintaining compression, Whenever overheating reported friend of mine would always check oil, then take of rad cap and turn over motor, if oil was milkshake and rad looked like old faithful no further checks were needed, not exhaustive or conclusive but with those checks no water pumps ect would be fitted. Thanks for posting I’ve learnt a-lot from your channel this novel electronic compression test is just one more simple yet genius tip, its great you do good work and share your skills much appreciated, Cheers.

[@tracycolorado]

Should have sent a camera in the bad cylinder , and pressurize the cooling system to see what size leak it was for kicks and grins

[@windward2818]

This is a good suggestion for a training video. But, after the block test you are at basically a stopping point in the diagnostics, as was stated in the video. The next step being, informing the customer that the engine has a head gasket leak, and if they would be willing to pay for a pinpoint test to identify the exact cylinder(s) that are leaking. Most customers just pay for the preliminary diagnosis and pickup the vehicle, to decide what to do next. Which usually translates to, will they pay to repair the car, and do they have the budget to do so.

[@davyarthurs]

At 08:05 when searching for misfire counters, I notified there is a magnifying glass icon top right, would hitting that give you a search box so you can search for the required data pid? Nice to see you back Matt

[@SchrodingersBox]

Hahaha yes it would have. To be honest I was just showing off how many parameters you get on that tool for the video lol. Actually the misfires are located under active tests anyway where you can turn injectors on and off to do a drop test.

[@davyarthurs]

@@SchrodingersBox 🤣 that’ll teach me for speaking up 😝. Handy features! Even better when you can do these extras without even moving from the driver’s seat😁

[@shepherdguy]

Pico makes a pulse sensor you can hook up to the radiator and scope. This would be a viable alternative to the misleading reading of the compression test.

[@TUNEITTHENTALK]

I could be wrong but i think the compression was a very minimal loss, the coolant fouling the plug was causing the misfire.

[@gilberthale7777]

Hey, Matt. Gil here, after a long time since I last posted anything (always good, never bad or hostile). I did not zoom in on the spark plug view at 38:24 to see if the electrodes on the darker insulator plug were more than the #7 plug, but if there is any more electrode wear on the #7 it might have been nominal at most. Anyway, the reason #7 could have been more white/clean looking is because having coolant (or water) in the combustion chamber, especially if ignition occurs even intermittently despite the coolant being present and hampering the ignition process, the spark will be getting steam cleaned in essence, and any byproducts of combustion that would normally be on the white ceramic insulator will be getting blasted off. I used to look at spark plugs and read them whenever I pulled them, even for a low mileage, otherwise good running engine, just to make sure there was nothing unusual going on with an engine. Any time I have one insulator far cleaner and brighter than the others told me we likely had coolant getting into the combustion chamber, and the customer would be coming in to get the misfire corrected with a self-assessed need for a tune up. Nope, no tune-up would be done. I would dig a bit more, using a compression test and/or BlockCheck. If they had a blown head gasket my replacing the spark plugs we not going to help. I would usually leave it to the Service Writer (Ford dealership in SoCal in the 70s and 80s) to break the bad news to the customer. Once the head gasket was repaired I would often get the car for a final scope and set, and if they really needed spark plugs I would install a set. Often someone else would have already installed new plugs in an effort to "fix" the misfiring caused by the blown head gasket. Gawd, the stories I could tell you... Anyway, good call on the head gasket, and Thumbs Up on not hammering the customer with even more asked of their financial resources. And, yeah, I would do the same once in a while for folks who came into our shop after trying to get a problem fixed by other places. My heart would go out to them as it means food off their family's table. The bad work was not my doing, but I was doing plenty well enough without having to be the one to bring more heat on them. The goodwill I got was tremendous, and I always felt good about being able to show that not everyone in the auto repair business is after their last nickel. Fair is fair, right is right - and I have neve rbeen hurt by trying to the right thing even with issues I did not cause.

[@SchrodingersBox]

Hey Gil good to see you back!!! Thanks for the great comment and hopefully we see you more consistently like we used to!

[@gilberthale7777]

@@SchrodingersBox heh heh, it is easy for me to get side-tracked. Retired, several vintage pony cars I n4eed to tinker on or work on during car Season, and lately I have been working on a special project that I think will be of interest yo you. Until I get certain paperwork filed and more testing done, I need to not get into it in a public forum. But, frankly, I thing this is going to end up being aa nicely disruptive game changer in several industries - to include auto diagnostics and repair. When I am able to provide more detail you are my very short list of folks I want to see what I have been up to. Early warning, put on your seat belt, you are going to need it... heh heh... It's all good...

[@charlesgould8436]

Thanks for your time.

[@SchrodingersBox]

Any time!

[@JJ-sv1ov]

As always, excellent video

[@mechanicmatt871]

Hi Matt, just a thought on the relative compression test, would it make a difference doing the test with the coolant cap removed, it may just help the pressure escape like it could on the leak down test. Just a thought. Thanks for another great video

[@SchrodingersBox]

totally agree. I think what’s happening is the cylinder is drawing fluid in but can’t compress it out so the compression is same as normal.

[@InsideOfMyOwnMind]

Here's your explanation for it. Consider the differential geometry of the cylinder as the piston travels vs the geometry of the leak. Pistons are fast. Leaks are comparatively slow.The compression tests in all forms will always lie in this scenario. Normally a compression test is only a valid diagnostic tool when you are looking for a substantial cylinder failure like a burned valve or a broken piston/ring, etc. A blown head gasket or even a cracked head is NOT a mechanical failure in the sense that a comp test is designed for. You did the right thing. Chem test, pressure back flow test and general common sense inspection. A leak down, removing all the dynamics of engine operation from the equation is great.. Even that however does not diff between a failed gasket and a cracked head/block. Some times a wet pressure test from the cooling side and a bore scope will reveal the actual location of the leak. There are KZbin videos that actually let you watch the coolant leaking into the cylinder through the head gasket. Cool shit. All my best to Jose here in my town of residence. And a belated welcome to you kind/smart sir. Now come back in mid/late August and tell us how well you like it here.🤣 We know.🤒

[@SchrodingersBox]

I think you are correct in your assessment of why the test failed.

[@christopherfranklin2262]

Matt use the search option next time. It's located I. The top right corner. It's great at detecting keywords. Thanks for the recommendation on the xtool. It's great

[@kinglangren]

Thanks I own the stool and it’s a little cumbersome at finding the needed pids. I squally just use a generic scan tool and go to the stool only if needed. Thanks

[@francoisoosthuizen6663]

Matt, love this video. Thanks

[@SchrodingersBox]

Glad you enjoyed it!!

[@frugalprepper]

I am wondering, if you don't see it on a relative compression test, because they pressure it leaking into the coolant system where the pressure cant escape. I would try taking the radiator cap off and see if it changes at all.

[@SchrodingersBox]

Totally agree. 100%. Or even drain the coolant. Or a pressure transducer on the radiator. But either way I absolutely agree that’s what caused the compression to be the same.

[@juansautodiagnostic6199]

I never use a compression gauge, i rather use a pressure transducer and a pulse sensor. more precises. great diag and great find.

[@SchrodingersBox]

What do you do if the compression is not lost to cooling system though?

[@juansautodiagnostic6199]

@@SchrodingersBox like a head gasket issue with a oil coolant passage. i put a pulse sensor in the crank case like where you fill up the oil and use a sync to figure out the cylinder. run the cylinder sync to a CKP or RC. Had one that had misfire in two cylinder and it was a blown head gasket that was 2 and 3 were compromised saw it in a rc test. leak down test or put smoke in cylinder 2 and saw smoke comer out on cylinder 3.

[@SchrodingersBox]

Makes sense!!

[@TerryBates-ic8rb]

Hi Matt, I agree with the other guys on using a pressure transducer on the radiator and sinking another channel to cylinder 1 to trace down the contributing cylinder following the firing order.

[@TerryBates-ic8rb]

Then verifying pressure loss at that specific cylinder via leak down test.

[@SchrodingersBox]

100% agreed!!

[@VashthStampeede]

Great video as always. Two questions about the relative compression test: Was the throttle fully open for "clear flood mode" and did you try it with the radiator cap off? Asking for a friend 😂.

[@SchrodingersBox]

Yes to the first and no to the second. However as you will see in the next video, the radiator cap will make no difference

[@reneneron2971]

Matt, the compression test doesn’t lie…it simply isn’t useful for conclusively diagnosing a bad head gasket. It is a basic test to identify the mechanical condition of an ICE to generate sufficient compression for combustion, nothing more. Coolant leaking into a cylinder (or combustion gases out) can be a trivial amount of loss of air compressed relative to that of the displacement of the engine cylinder…for a 2 liter,4 cylinder engine, 500cc of displacement compressed (on EVERY stroke) relative to what may be a pinhole sized leak in the head gasket. Science. A blow-by (leakdown) test or the chemical test of the coolant, both of which you show, are far better tests for detecting a failed head gasket than using a compression gauge, and are just as fast (or faster). That is the explanation…science. Last, since you are an educated man, a diagnostic test is incapable of lying. The results provided may be misleading or inconclusive, but lying is the intent to deceive (knowing information is false). Lying requires more than just data or information. Data doesn’t lie…people do.

[@SchrodingersBox]

Agreed. I should say it is misleading but you are right- it is reporting the conpression accurately

[@l.c.9596]

hello, really like your videos, been watching them for few years now. which auto scanner would you recommend for a do it yourself guy working out of his garage that will have 2 way communication that will do everything that somebody working out of his garage will need to do without breaking the bank? thank you and keep up the good work Sr.

[@SchrodingersBox]

I think the XTOOL is a good choice. Under $400 and has bidirectionality.

[@remodz6385]

You can’t excuse the shop so easily! All they had to do was what MOST people do when they suspect a BHG, a chemical test. It was obvious

[@mustangguy8981]

Compression? Or chemical.

[@mustangguy8981]

I ask honestly cause Idk. But I haven't finished the video either 😬

[@mustangguy8981]

Oh dear Lord... Never mind. I thought there was some kind of advanced type of chem test. This is very common stuff. My bad. I'd have just done a pressure test to begin with a kit.

[@mustangguy8981]

Wow, 27 min in. You humored your buddy, proven that a compression test can't always be counted on over a simple code, and so far, shown the most efficient way of where the coolant is really going. Nice man. Do I have your consent for a brain transplant?? Lol

[@mustangguy8981]

I've finished. Thx for the video.

[@robertjospeh1097]

Can you use a radiator pressure gauge to check? If it pushes that much coolant it should be easy to measure with a pressure gauge. You would be checking all cylinders at once.

[@SchrodingersBox]

Yes indeed you can use that if there is significant enough coolant pressure. But it can be subjective as coolant pressure increases anyway because of temperature.

[@robertjospeh1097]

If there's not a problem it should not increase past the rated cap pressure though, if your getting exhaust gases it should go right past the rated cap pressure I would think..@@SchrodingersBox

[@spinmyhead1667]

Ima find it hard to believe 2 shops couldnt diagnose that.Could be a case of a customer concealing information.Indeed you said it yourself,now your armed with the knowledge and expertise you have become the bad guy,as you have inferred the 2 previous shops as being.

[@jimskinner2777]

Matt, isnt there a transducer that can be hooked to the end of the exhaust? Would this not show cylinder compression of some sort? Love your channel and content

[@SchrodingersBox]

yes you can do that for sure!!

[@charlesgould8436]

Saw a 92 accord, no brakes unless you pump, obviously been filled, no visible leaks. Customer says a cylinder issue. I have had a 93 Sanoma...self bleeding:)

[@Lambros_Stefaneas]

i know it's a bit expensive as a tool, but using a gas analyser, is the easiest way,more accurate, and much faster than the other tests. less than 10 seconds. you stick it in the cooling cap,and done.that we was doing in the previous workshop i was working. and even if you don't own, i am sure its going to be something near by.i will suggest you Matt,to give a try to this technique, and share your thoughts.

[@Christdeliverme]

Welcome back homie

[@SchrodingersBox]

Wah da tah my damie!!!

[@kerryb2689]

Bernie Thompson has a pressure transducer that he uses a scope to measure the pressure pulses in the coolant, then syncs to #1. That may be way more sophisticated than you want to do, because most do-it-yourselfers can't do it. Small leak, large displacement = little compression loss. I don't understand why when you give it throttle you get more white smoke....more throttle = less vacuum sucking coolant in..... unless it's when you let off the throttle after pressurizing the coolant with more throttle.

[@alexlee4573]

Excellent! Thank you Mat! Super Mario has an interesting video named "Don't trust relative compression test".

[@SchrodingersBox]

I will have to watch that!!!

[@Jason-gd4qr]

Wondering if there is something odd going on with the scope measurements. It seems the voltage measurement is dropping when on the open compression stroke where you would expect to see the voltage high as the load is reduced for this period. Could it be some strange poor grounding of the scope related to the high current measurement.

[@SchrodingersBox]

Hahaha great eye man. Others brought that up as well. Really good eye. Its because I intentionally reversed the polarity so the waveform would look more familiar to what most of my viewers are accustomed to on compression testing. You are absolutely right though- on normal polarity you will see the opposite pattern in voltage.

[@secondwindmusicproductions]

How about a pressure transducer in the radiator cap synced with a pulse from number one cylinder to find which one has the blown gasket?

[@SchrodingersBox]

Exactly what I will do in next video!!

[@Anglosax007]

Hi from the other side of the pond, been in diagnostics since it started, 25yrs, must be mad, But great approach to the car, but one thing I was thinking is, can you not do a RC test off of the battery directly with the Pico ? I don't use a Pico, I tend to use my trusty old fluke/tech31 as it has a lovely bar graph for RC tests and just clips on to the car battery? I'm sure I've seen someone else do something like it in a Pico. Just think it may be more of a delicate indicator if that all makes any sense? On tech31 it shows all cylinders in % from 100 down . Sometimes you just can't find what it is, but boy does it get to you not knowing, I love doing autopsies on anything that's failed just to know why. I started doing that about 10yrs old to mum and dad's black and white TV, I was grounded for weeks. Lol All the best guys

[@timothymay8917]

the coolant in the cylinder is displacing air thereby raising the compression

[@SchrodingersBox]

Agreed. That makes the most sense. The coolant can’t leave as fast as it entered so compression isn’t changed.

[@DuaneDonaldson]

Commenting as I am watching. Does this tool show a dead module in the full count of the number of modules or it simply skips over it and not enumerate it like some other scanners do? The reason I bring this up is many folks like to know how many modules are on the car that they will work on so for future videos that you scan with this tool, may I pls ask that you scan the vehicle, get the full count on the first go around, then once repaired to do a post-scan, double check the module count to see if one came back to life based on the repair. Some more expensive scanners have a full count near the top of the screen, dead or alive. An RC Test is only a guide, coolant leaks inward to the cylinder on the intake stroke while compression does not leak into the cooling system strongly on the compression stroke but may leak during the power stroke if actually running, during the test this would be the expansion stroke with no real effect, at least not proven as you did not do a compression test on the radiator which may need a very sensitive tool for the scope, you also did not check for an intake vacuum problem which also needs that sensitive tool. Some head gasket leaks seem to be one way as the blown gasket acts as a one-way flap of broken gasket or something like that, many I have worked on only leak when sitting all night and cooling down and allowing the coolant into the cylinder during the cool down cycle only. Up until 18 minutes, you did not use a sync signal to ID which cylinder in the firing order was the actual low compression positively identified with the RC test, although very slightly. Very likely the oil cap was from this issue but need to know if the owner does regular oil changes and more so do they do a lot of short drives, this will condense water in the crankcase quite easily. To read that spark plug we need to pull 2 plugs to see if this one is washed and the other has black or brown residue as an additional verification. In some cases, the plug will be colored/tinted the same as the coolant. Your second RC test is definitive but imagine the first RC test, where is the compression loss going, its a practically full cooling system, so where is the loss going, it must be minimal, drain the coolant and try it again to see what an installed radiator cap and an installed spark plug with an empty cooling system looks like on the scope. Your scope has the ability to clean up all that red noise, I think with a better/cleaner capture you will see the problem easier, I can see the repeatability on the later tests also. Manual compression gauge, first pulse over 90PSI, no problem with rings, no cylinder washdown based on burning coolant so any other compression leak is small and not noticeable via this method as you have stated. Looks like it is too late to compare spark plugs as the previous shop charged them for work that did absolutely nothing to fix the car, and took away the ability for the next mechanic to see the problem right away, (possibly) BIG SURPRISE. Known good cylinder manual compression also over 90PSI on the first pulse, the ring inspection pulse (if low, do it again as you may have already been on the compression stroke and got cheated out of a full stroke). Cutting their losses can be your honest gain, buy it from them Bro. ON YOUR SIDE HERE, if you saw the original spark plug on #7 and compared it, you would have found the problem ASAP. Possible mistakes, red waveform too noisy, blue waveform too short in height, only reading one spark plug (no help in this case but you didn't think of it up front), not syncing the amp wave to a cylinder ID like #1 on a second channel, I believe with a better scope setup, you also would have found the exact cylinder ASAP. THUMBS UP

[@johnkaplanian]

Dear Mr. Mat, Thank you as always for your detailed informative tubes that emanates from a highly integrity soul which is rare in this digital world Lool. Therefore, be sure always that you are a Rolls Royce in supremacy among Humans Lool. I am gonna give your client an advice based on one more check to do which is: Open the radiator cap while the engine is cold or slightly warm and fill it till the neck's top, and start the engine and watch for the amount of bubble going out from the radiator neck of which it may be very tiny intermittent or not constant at cold and might be gone away when the engine is at operating temp. However, and based on smooth engine sound as is in your case, you may (but I am not sure) not be able to see any bubble from radiator neck, specially when the engine is at operating temp.. So my advice to the client is to keep a jug of distilled wated in the trunk, and each morning before warming up the car to check the coolant level and top off a little bit till the top of the neck and live with it, and ofcourse to change oil every 3000 Km, or about 6000 Miles. I say that because I have had a honda accord with a exact similar situation with a very smooth engine that lasted so many years. Another FYI note is that maybe the pressure setting of the leak down tester to be no more than 80 PSI as a standard. Enjoy your time and Take Care. John Jack Kaplanian from Jordan / Middle East.

[@davidvick2616]

What about doing the relative comp test with the radiator cap off so the pressure has somewhere to go

[@SchrodingersBox]

As shown later in the video it makes no difference.

[@waynerogers2706]

Food for thought. When metal is cold, it contracts, when it's hot it expands. A cracked head makes more sense with all your tests than a head gasket does. I haven't finished the video yet, but my mind is screaming cracked head.

[@SchrodingersBox]

Yes but temperature made no difference. I believe it’s because coolant pools in the cylinder and can’t be pushed out as fast as it drew in so compression is the same.

[@dimisrambodimisrambo7285]

when we get compression from the battery poles, at what value do we put the picoscope? others say to put ac, others dc. what do you suggest in terms of values ​​and at what time do you put it? I understood the 20v, what time do you use? msec sec?in the specific video, for example, what values ​​have you put in the picoscope?

[@SchrodingersBox]

I will show this much clearer in an upcoming video.

[@walangbuhok1]

Monster Matt, you are the best!

[@robertmedina6875]

You should buy the vehicle Matt. It would be a great video!!!!!🎉

[@SchrodingersBox]

Golly I am tempted to get free the customer $200 to bring it back and let me experiment it for a weekend.

[@towniespore5179]

What about testing the pressure in the cooling system and see how high it goes

[@chriswest9574]

Matt, do you think it could be possible that a cylinder could achieve full compression just at the point were the pressure escapes through the damaged gasket? Much like certain spray bottles that build pressure before they release. Your thoughts. I appreciate your dedication to the craft.

[@SchrodingersBox]

Yes I agree. I do believe that explains it.

[@billmonroe8826]

Just because it's a shop doesn't mean they're professionals! What's sad is the fact that they wanted to spend $4000 which would be a complete loss to the customer because the major problem wasn't fixed. The shop just wanted to do easy stuff!

[@SchrodingersBox]

I absolutely agree.

[@burntkorn]

I wonder are you not seeing the compression loss because with the radiator cap on and coolant in the system it’s basically sealing it off ? Would it show up on the relative compression test if you tested with the radiator cap off ? Well I should have read the other comments I see someone already suggested that idea.

[@SchrodingersBox]

No I have other videos that show the radiator cap makes no difference. And we know it wouldn’t. The compressibility of coolant in the cooling system is clearly demonstrable. It literally makes no doffeeence with or without cap on.