How to test a temperature sensor / sending unit and temperature gauge

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I made a video to help understand how a temperature sensor / temperature sending unit works and also the gauge. This is from a mercury outboard but the same principal works on any boat, car, engine, etc. temperature sensors. Pardon the stumbling, this was one of my first lengthy videos. The final outcome is that this Merc sensor didn't quite match the gauge readings. I will probably use this gauge and just keep in my mind it could be about 30 - 15 deg off in the important areas. I still don't know what the 700-850ohm label is on the tag, but it is NOT the range of the sensor.

[@kellyplanuk]

Thanks for taking the time do do this video. I found it really clear and informative.

[@pmessinger]

Very nicely done. I'd like to test a sensor on a 4-wheeler and you've demonstrated the process to me very well. I need to see it done by someone who understands the procedure to assure I don't destroy more than I measure.

[@sshawn09]

Good luck with that, shout if you run into any snags.

[@mauriziopescatori4606]

I had a smiliar issue with a *mechanical* water temperature gauge. I did exactly as you, but omitted all the electrical measurements (mechanical gauge). The BIG ISSUE is : "What is the gauge reading when water boils?" Water boils at 100°C - 212°F, and THAT is what counts. In my case, the gauge read a bit shy of 210°F, so I knew the reading was off by "the thickness of the needle tip" However, in a mechanical gauge, even the slightest mesplacement of the needle during manufacture will cause such misreading. So, overall, I'm satisfied.

[@franklinarguedas4832]

Your video is quite instructional. Would you please elaborate on the breadboard set up that you have, I would like to copy that for my hobby work. Excellent work, keep it going, it would benefit lots of people interested in the field of electronics.

[@dekebell3307]

Thanks for making this. I'm dealing with a gauge/sender issue and your video was a great lesson. Thanks!

[@shawnschembri29]

Glad it helped!

[@sshawn09]

If you can, subscribe to my channel, with enough subscribers I can get a small kickback! Thanks in advance!

[@robertrider3329]

Great video. I know this is an older post but that is not a temperature SENDER for the gauge, Hence the tan and Blue wire. It is the overheat temperature SENSOR for the alarm buzzer, Hence the narrow ohm range. The correct temperature SENDER is a screw in type with a TAN wire that goes to the Temperature gauge. Maybe this will help someone else with a similar issue.

[@DXMediaTV]

Calibrate the gauge to the sensor values. Usually one screw adjuster at the back of the gauge.

[@Anthony-du3he]

Thankyou sir. I have the manual but this helps see the process

[@blakemccorkindale4398]

The manual you guys are talking about is the mercury manual? I have a seloc

[@marino7im]

where did you get that bench test unit, name and model. How much also. BTW I loved this video on how to test a temperature sensor ' sending unit and temperature gauge. It is exactly what I have been searching for. Can the ohms test be effected by leaving the units in the engine when doing the ohms test?

[@sshawn09]

+Marino Im E&L Instruments CD-1 CMOS/TTL Designer Prototyping Breadboard, I forget where I got it but its neat right? If its in the engine, it will be at whatever temp the engine is at.

[@billwilliams6338]

SSHAWN09 ))----- = Can I just "back probe" the temperature sending unit and put my ohm meter to read the ohms while the car is idling to measure the ohms of the temperature sending unit at different engine temperatures? But how would I know if the temperature sending unit is good or giving false readings? I don't know how to test the temperature sending unit or where its at in cars. I'm not sure if the sending unit means a sensor. 1.) How do you test or what do you use to test the temperature sending unit? 2.) Can I buy a digital gauge at PEP BOYS and install it in the fuse box wires by slicing the wires to test if the analog temperature gauge in the car dash temp gauge is reading false reading measurements of the temperature? 3.) Can you make a youtube video showing how to test the car dash gauges to see if they work correctly and not reading false readings and how to test the sending units to the cars gauges? 4.) I don't know how to test the cars gas gauge, oil gauge, temperature gauge using a ohm meter or what other test tool can I use to test these gauges are working correctly and not giving false reading or not working correctly?

[@blakemccorkindale4398]

That line graph and specs came out of mercury manual? Is yours digital? Where from?

[@sshawn09]

@@blakemccorkindale4398 digital copy of a merc manual. It's been a while, forget where and how obtained.

[@MrTarkus007]

i have a grumman 85 &temperature gauge not working i get hot air what should i do ?

[@sshawn09]

+mario d.c Sorry I am unfamiliar with the setup.

[@paulzarpaylic8772]

Checked my sensors on my 90 :-P Suzuki and both checked out good.However my temp light stays on at the gauge even when engine is cold.

[@sshawn09]

Perhaps it is wired wrong? I am unfamiliar with that setup, is the light controlled by the gauge itself or does it have another feed from somewhere else? If the latter, then chase down that path.

[@AussieDors]

Thank-you for the video. I know its 6 years old but how do you remove and install those thermosensors?

[@sshawn09]

Thermosensors, not quite sure honestly.

[@daviddore-smith3467]

sshawn09 no worries. They just pull out and push back in. Couldn’t be easier!

[@jimnjele.bean-dayone3505]

I'm curious if you ever opened the gauge to see if there may be some type of calibration inside the gauge? Nice test setup !!

[@sshawn09]

I never did, that's a good question though. I'll consider it if I ever come across it again. Only issue would be that I would need to convince myself I have a good truth source.

[@stevenpatterson9162]

Great video and well done. It was sad to see the accuracy drops off tremendously as the temperatures rise. I personally believe that all outboards should not go over 170 degrees. I was surprised to hear and see the horn doesn't sound until 240 degrees! Doesn't deactivate until 210 degrees...not good! Outboard motors are not built as durable as car motors..... My favorite part of the video was when you say "nothing fancy". Although the sender units should be located at the top of the heads, normally there are rubber diverters in the channels of the block which sometimes get clogged causing one to guess if all of the motor is being cooled. Would you know how to build a 6 sending unit temperature kit with sensors with digital display to read all six? (cheaply)

[@shawnschembri29]

Steven, Thanks for the good comments. Please dont confuse me to be a boat guy, I'm very new to boating and new to 2 stroke outboards as well. The horn is certainly a "youre screwed" moment"! On my Merc 200, the sender for the gauge is an indentation within the head, which I believe you know. On the opposite side of the engine lies the horn sending unit. So 2 holes, 2 measurements, 2 different banks, and lastly, 1 of 3 carbs controlling that cylinder, but due to the mid location of the sensor, 2 of 3 carbs really effect the measurement. I personally feel that cyl head temp is crap b/c it takes a bit of time to heat up the head, and the validity of the sensor reading cant be proven too well b/c it sits in a hole and has a slow measurement. I'm an engineer, and love tight tolerances. If you truly want to see if you are melting your cylinders, you probably want an exhaust gas temperature gauge but that would be a bit expensive and will not give you a reading per cylinder unless you install 6. Multiplying the cost by 6 as well. Perhaps another method would be to tap a probe into the water (cooling) flow just like your car has. It is an alternative but still has its pluses and minuses. In engineering world, we have thermocouples that you can adhere to any surface and get temperature. That would be your best bet to read what all 6 are doing, but it will be approx, and what you'd get out of it would be knowing if 1 bank (of 3 cyl) would be leaning out, or I should say carb. In my engine, 1 carb for 2 cyls, with 1 jet meaning it gets split up, so 1 bank would be 2 opposing pistons. Now to read that, you would have to look into a all in 1 type gauge. I own a "Innovate motorsports LM-2" which I can put 4 analog signals to it and get a reading, and furthermore data log. All that wiring and the fact its not made for salt water, it would only be a temporary install. Where there is a will, there is a way, but it wont be cheap, and it would be questionable if it is worth it. If you use the boat regularly, you will notice engine perf differences and leaner conditions. With the ethanol crap out there, I feel its best to service your carb before the season starts, know that you have clean jets and clean flow, and the chances of overheating become slim. Hope that helps a bit... I love instrumentation and would be glad to discuss more if you really wanted to make a project out of it.

[@stevenpatterson9162]

Shawn Schembri Shawn, never confused you as boat guy at all! Make no mistake you are truly an engineer! With todays requirements from EPA on 2 stroke motors, our outboards are running much leaner than they used to with no adjustment allowed unless you want to risk blowing the motor or fouling plugs. I have (3) Yamaha 300 HPDI motors one which just blew cylinder #2 piston with no warnings! They are fuel injected and have a total of four filters that have been serviced regularly. Funny you said cleaned and flowed....That's what I will be doing to the motor when I get it all apart the fuel injectors that is. While I am there mine as right! Its like, mine as well put new rings on the other pistons..... I ended up buying another HPDI 300 Yamaha so I don't have any downtime and can rebuild in my leisure time. Just installed it today. Bobcats are wonderful machines! I have the YDS (Yamaha diagnostic software) which only showed some overheats with the highest temperature being 187 never had horn sound. No other faults shown on software. I repair control panels with automation circuitry for irrigation and have been always amazed at all the little automation toys you can put together with the help of a circuit board from a security system. Here's a site you might be interested in some day....www.sentex.ca/~mec1995/circ/circuits.htm Nevertheless, 2 strokes are much lighter than 4 strokes and quicker to get up and go. When fishing the bays most those fish are in skinny water so you need a lighter motor to get you in and out of their territory. I have owned many 2 strokes that have never blown a cylinder and I believe that my motors need more instrumentation and possibly some more safeties that will not allow a cylinder to go south again. Many mechanics I have spoke with say "it's always #2 cylinder on those HPDI motors" and when asked why they say that "we do not know why, nor does Yamaha". Which is a true statement because I have even spoke with Yamaha directly. They did have a recall on the oil pump which I have on all my motors. Sooooo, I will get to the bottom of their problem... I definitely would like to make a project out of it! One sensor per cylinder (6) total communicating to a large display. www.westmarine.com/engine-temperature-gauges/faria-instruments--cylinder-head-temp-sender--10704583 I had these on my upper two heads on a Johnson 140hp 4 cylinder and they worked great. Simple...installed behind one of the head bolts. Maybe use these but as far as a display that would work with reading all six...??? Know of anything out there? Lets talk about the dash....gauges with needles are boring and quite honestly do not catch my attention...With importance of temperature I would like to have something bold and bright/modern. What do you think?

[@chevelle68]

Good job

[@shawnschembri29]

Thanks, glad I can help

[@sshawn09]

If you can, subscribe to my channel, with enough subscribers I can get a small kickback! Thanks in advance!

[@psycopper1]

you can calibrate by using another resistor in parallel..

[@sshawn09]

If I understand what you are asking, you are asking if instead of boiling the temp sensor, can you use a resistor right up to the gauge instead? If that is the question, then my answer would be that you can, but the one unknown is that you are not 100% sure that the temp sensor is reading what it should. As critical as a temp sensor and gauge are on a boat motor, I want to see and prove that everything is what it is. For instance, if you are TOLD that the temp sensor is 220 deg at 100ohms, you can drop in a 100 ohm resistor and cal your gauge, but do you trust that the temp sensor is accurate? Has it crept in the years you've owned it? Has salt water squeezed into the wire causing corrosion and additional resistance (** note, this can happen in the rest of the harness you are not testing that is on the boat, but at some point you got to draw a line and say thats too much effort to ring out the whole harness). Has "Joe Hackanic" replaced the sensor with one that fits that was sitting around the shop? There are a few different scenarios that can scare the crap out of you. I think its worth the effort to go through the complete proof. Engine temp is your last resort to save a motor when out at sea, and we know they are not cheap. Hope this helps =)

[@frankdavidson9675]

i have a simpler method that works if you can get several 100 ohm resister twist them togeather end to in a string clip one end to the sender take the wire you lifted off clip to other end of resister string take your this test is in the car so turn on switch gauge should read low now start cliping to the resisters going toward the sender watch the gauge it will start going up the closer you get to the sender the higher it gos this will tell you gauge is ok replace the sender

[@mcconn746]

Good job...thanks. The range of Mercury's chart is terrible. The lower part of the chart should be cut to make the higher part more accurate. I hope they will redo it.

[@shawnschembri29]

Agree!

[@sshawn09]

If you can, subscribe to my channel, with enough subscribers I can get a small kickback! Thanks in advance!

[@mcconn746]

Good video...but rather than comparing ohms on the gauge and multimeter, why could you not just hook up the gauge to the sensor and compare the boat gauge reading to the thermometer...assuming the thermometer is correct. You could check the thermometer at 212° in boiling water. You might want to take in consideration the elevation if you are in the mountains.

[@shawnschembri29]

It was to ensure that the gauge was doing what it should be, because I was seeing variability on 2 different gauges.. I guess you can call this a "piecemeal" check?

[@sshawn09]

If you can, subscribe to my channel, with enough subscribers I can get a small kickback! Thanks in advance!

[@irajeshtailor]

In My Car From the last month I am facing weired issues: - Fuel Tank Got Shrinked Which caused wrong fuel indication. After installing a new Tank i am seeing whenever I open my fuel tank cap, air vacuum releases. - Another problem is. My temperature gauge is going 1/4 only. 2 months ago I serviced this car. Oil change, Oil Filter change, Air filter change, Installed thermostat which was not installed before, After servicing I ran 150kms. Everything ran fine, But now I am facing these two issue. Steps I have taken : Checked temperature guage by grounding it. It works fine. So I installed new temperature sensor. But same thing happening.

[@sshawn09]

This depends what kind of car you have and all that, if it is solely manual then you can test the gauge by applying the correct resistance value, but today's cars the gauges are fully controlled by the ECU so it's really hard to try to even guess over this conversation

[@irajeshtailor]

@@sshawn09 tested the guage manually, it is working.

[@sshawn09]

@@irajeshtailor must be the signal then that the sensor is sending then

[@vampov]

This is way too much work I'll just buy a new one and replace it.

[@shawnschembri29]

My purpose was to understand the accuracy on a motor that was setting the overheat alarm. Regular replacement is always the way to do it unless you suspect a different issue.

[@mikehallmark8374]

You worked way to hard on this deal all you had to do was make a glass of ice water put the temp probe in it should have read 0.0 ohms.

[@shawnschembri29]

Perhaps but I do like to experiment and see the accuracy along the range of the sensor. In my case I was getting the overheat alarm and needed to know it was true.