How Hot is Too Hot?

[@LTVoyager]

My primary instructor was also the airport manager and A&P and he said shock cooling was BS clear back in 1978. His C150s routinely reached TBO and they were “shock cooled” on every pattern circuit as he taught us to make all landings as power-off approaches and landings. I am glad to see the industry finally catching up the him.

[@Pilotman28]

Your instructor was correct way back then but you were not in danger of shock cooling the cylinders from pattern flights. You need very cold for an extended period of time to have enough of a thermal difference to make the rate of change high. Shock cooling would need to be darn near intentional to happen.

[@LTVoyager]

@@Pilotman28 Correct. My comment was meant to be sarcastic for all of the “shock cooling” disciples. I edited my comment and added quotes to make it more obvious.

[@JimmyH-q5i]

Hi, I continue to log more than 20 hours, listening to your videos, which are excellent, thank you so much for your efforts.

[@darrylday30]

Much appreciated. Thanks Mike. You’re making me a better mechanic.

[@apfelsnutz]

25 reduced to 20 will certainly make your engine easier starting... I hate to see people cranking and grinding on the starter even when cold. This tends to indicate to me too much advance on the timing... well worth considering. Good syminar Mike !

[@johnschreiber1574]

Ion sensing can show peak pressure in relation to timing using a normal spark plug. SAAB pioneered this technology in cars circa 1990. Most current coil on plug auto engines are using this technology. I will comment further in a later post.

[@dwdjr6937]

Do these CHT guidelines differ with a LOW compression ratio engine as opposed to a HIGH CR engine, or does this apply across the entire CR spectrum?

[@garysulin]

Thank you. Super interesting and informative

[@swlowry5277]

I recently asked a Continental Engine rep. He said their CHT's like to be 375 - 385 and can run all day at 400 degrees fahrenheit.

[@BonanzaPilot]

tbo is almost 70 days though

[@kevin_6217]

Ha!@@BonanzaPilot

[@jamesharris4744]

Learned a lot. Thank you so much

[@doughamilton1756]

Great information, thanks 😊

[@BonanzaPilot]

I generally keep all my cylinders under 380 on the TSIO-520's I run in two Bonanzas. 110 degrees and Heavy out of palm springs or something similar, Keeping the hot cylinder under 400 is a chore, but normal operations 380 is no problem. I'm more curious about the "optimum" or "sweet spot" because that 380/400 is for my hot cylinder, in a climb, on a hot day... My coldest cylinder doesn't really get past 350 in any situation and keeping it above idle temp in the decent can be tough.

[@savvyaviation]

This sounds reasonable for the operations conditions you describe. You're not doing any harm there.

[@ozelot250]

I have a 1952 C35, my 1&2 cylinder routinely get to 400-460 during extended climb. I live in desert south West summer temps get to 110-120 f, this is only a problem during climb once at cruise temps are around 350-400. How can I keep emergency cool during climb? Full throttle, mixture full rich, rpm 2300, 100-120 climb out

[@cdeggz]

You mention that drilling the holes in front of the front cylinders was not going to help, and in fact could make it worse. what is the "proper" fix to improve the cooling on those front two cylinders?

[@stevespra1]

I cannot get my IO-540 to run above 300°F. I've heard these numbers before and am very interested in managing my CHTs. We bought the Cherokee Lance (PA32RT-300) with a fresh overhaul. It did not have an engine monitor for the first 400 hours or so until we installed an EDM-830. I was very surprised to see the CHTs never get above 330 in a climb and run around 300 at cruise, slightly lower LOP. I would not think that the 1978 cowling (designed in the 60s) is better than modern design... However, my friend's '69 Arrow is the same.

[@Stepclimb]

Below 300 is unusual. If you can confirm with a thermal IR gun that your CHT instrumentation is accurate, you might have a timing issue. Retarded ignition timing will decrease peak cylinder pressure, increase theta PP, decrease HP and also CHT. Have your magnetos timed with a Time-rite digital protractor (not a flower pot or using the marks on the flywheel). Make sure to use the piston plug and the digital protractor to precisely determine TDC. Look carefully at your TCDS as well. Many Lycoming angle valve engines have optional 25 degree (vs 20 degree) timing.

[@jimaddis2]

I’ve got same motor and issue in my Saratoga. At 30 degrees rich of peak, hottest cylinder is 330 and lowest around 298. About 1100 hours on engine

[@savvyaviation]

Are there cowl flaps? You can use them as needed.

[@stevespra1]

@@savvyaviation There are no cowl flaps. The interesting thing is, my friend's (who is also an A&P IA) PA-28R-200 also runs cool. Is this a Piper thing?

[@askmehowiknow3571]

@@stevespra1 my Piper Comanche 260b with an IO-540 with a JPI engine monitor runs about 315 degrees for the front two cylinders (give or take) up to 350-360 in cruise on the back two cylinders. It has 1300 hrs on it and I have not had any valve sticking issues. I recently performed the lycoming service bulletin 833c and none of the valves had any sticking issues. But I’m not sure why the front two cylinders run that cool in cruise. I do, however, fly 10.5 and 11.5 k feet regularly and run slightly ROP and close to peak.

[@HOSSDOG3]

What CHT is too cool for the lycoming IO360? I’m using your leaning technique and I’m getting around 300 degrees and 9.0 gph. New pilot new plane to me 1984 m20J 900 SMOH. I don’t want to ruin my valves by going too cool.?

[@heaye]

very thank you!!!

[@RaceMentally]

Is there a video on oil temps?

[@Bearhawk_Life]

Great stuff, I am now a new subscriber

[@savvyaviation]

Welcome aboard!

[@austincustomcnc]

I’m running about 320F in my IO390 RV-14. Seems too low all of a sudden

[@swlowry5277]

Is there any real data on delta engine cooling temps on descent? How much cooling is too cold??

[@sacuW9ep]

He discusses that during the questions at the end.

[@ozelot250]

What would be emergency procedures to try to quickly cool engine?

[@backcountyrpilot]

Ozelot250- lowering the nose and reducing power and richening the mixture will cool an airplane engine.

[@zirkspruyt6670]

Stugling to get my IO-520 B36TC 1983 to run LOP runs rough way before CHT temps drop as required. My Question is if CHT is below 380 and TIT below 1650 does peak pressure still have a effect . I am thinking about lowering Rpm and Manifold pressure to a level where the temps are as required?

[@Personanongrata69]

Call GAMI. Your setup isn’t tuned right. There is no reason you shouldn’t be able to run LOP without any issue whatsoever.

[@RD2564]

Not a chemical engineer, mechanical engineer which is of course much better still (lol): 1:04:30 the bottom portion of cylinders do not have much heat from the combustion process because the piston doesn't go down that far so no need for fins, not hot enough to justify fins. 1:05:25 : Yes, excess fuel absorbs heat because liquids have much higher heat capacity than the vapour which is most of the substrate. Good question.

[@kabaddiify]

Love it

[@dermick]

If you run UL fuel, is there any reason to keep the CHTs hot? No lead scavenging issues if there is no lead.

[@shinrarvallar]

He addresses this a few seconds past the 48 minute mark. "Probably not"

[@jonilu3473]

Thank you for all your webinars- simply sensational! I own a TR182. To stay under 400 I have to use. Cowl flaps party open. I this a problem (because open flaps dont reduce ICP) or ist ok to be under 400 also with flaps open? Thank you so much for your answer!

[@TheReadBaron91]

Wonder if that was the first time that Cirrus’s engine was redlined

[@davidwhite2011]

You can buy pin striping tape 1/32" (in many colors_ to mark your gauges on the glass and I would for airspeed and temperatures.

[@savvyaviation]

Markings must be in accordance with the aircraft type certificate data sheet... (TCDS).

[@David-p7z9n]

Continental tried shock cooling cylinders on a hot engine in the test cell by repeatedly dumping gallons ice water on the cylinders, nothing happened. It’s a myth. A&P/IA

[@derheeheehee6941]

Whatever the maintenance manual says

[@jjchello]

That’s not good advice. If you’ve been in this discussion for long you’ll quickly realize that aviation piston engine technology has been completely neglected in regards to innovation and advancement. Most “new” maintenance manuals were written in the 70s and that’s if you’re lucky. Even if the date of the manual says otherwise, the actual information is antiquated. So much has been gained in understanding by independent testing and borrowing from automotive developments that there is far better management techniques outside of maintenance manuals. TBOs that blow the manufacturer recommendations out of the water.

[@derheeheehee6941]

@@jjchello The information contained in SB's, SL's and SI's augment the lackings of the 1974 manual. The latest revision of the OHM is indicated at the beginning of the manual. None of it is antiquated.