High CHT C172R - Concerning?

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RocktheWings

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RocktheWings
Flew a new plane yesterday and noticed the CHTs (particularly the #4 cylinder) was quite high on takeoff, tipping 425 and climbing (other cylinders about 405-410). I reduced power and monitored everything and was able to manage it all and keep it around 390-410 most of the time doing some pretty benign maneuvers. EGTs all seemed normal too and kept it full rich for additional cooling.

The plane is a C172R with 160hp, and I’ve heard that Cessnas don’t have great cooling, but for that kind of power output the CHTs seem excessive. I typically fly 180hp S models and the CHTs stay around 355, and on long extended climbs maybe hitting 385, so this seemed fairly abnormal.

Admittedly I don’t know the complete story on the plane as it might have a rebuilt engine in it and is going through its breakin phase, need to check on that. My basic knowledge has always been 380-400 caution zone, 400 and above do something.

What are your thoughts? How concerned should I be?
 
Sounds a tad warm. The usual list of simple things to check would include ignition timing, fuel flow (is it enough at full rich?), and proper position/condition of baffling.
 
Rgbeard said:
My $0.50 bet is on bad baffling.
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I agree, particularly if I understood correctly that even in cruise he was full rich and less than full power to maintain 390-410...

Alternately, are the probes known to be accurate? Doubt they’d all read high, but...
How was oil temp?
 
Yea, off memory, normal power setting (~2100 for cruise with the R model) would get into the 390s for head temps. Lower than that it would start to come down, but not by much. Luckily the plane has an engine monitor on it and I took a few pics.

This was right after the engine run-up. Conditions outside were 20*C, low humidity, sea level.

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And this was right after an initial climb to 1000ft:

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EGTs all seemed normal and relatively uniform for various flight conditions, same with fuel flow, and oil temperature seemed ok off memory as well.
 
450 is allowable on that engine. Those temps are high but acceptable. First thing to check is timing on the mags and baffling.
 
Did you just borrow it, rent it, thinking about buying it, or what?
 
Shuswap BC said:
Did you just borrow it, rent it, thinking about buying it, or what?
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Renting. I don't know all the details behind the plane, but within the last 6 months they found metal shavings in the oil filter, which prompted an engine replacement (or rebuild, not sure which one), then had an engine failure due to a fuel line not being sufficiently secured, and now here we are. So the plane is still in it's trial run phase, but things still seem off imo.

Part of me wonders that if other students and renters are flying this thing without paying attention to the temperatures causing excessive heat and the previous metal in the oil. I put a lot of emphasis on engine management in my personal flying, and as mentioned it took some work to keep everything under 400, I doubt the general renter is doing the same.
 
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James331 said:
Never heard cessnas have bad cooling before
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Was that a joke?

Actually I had several A&Ps tell me the same thing when I complained about high CHT readings from my JPI 700 in my 172n. This was 10 years ago. I asked them how many 172s they worked on with multi cylinder engine analyzers. Most of them said "none" becasue 172's don't need them because they are bullet proof.

They were right. My 172 with high CHTs ran perfectly fine with those high CHTs, until the #4 cylilnder exploded in flight causing us to have to set down on a rather busy road at rush hour. Fortunately, no one was hurt. I never did find out WHY it always ran hot. I had several A&Ps check it out, including the "expert" at the engine shop that did the last rebuild on it. I told other A&Ps and they invariably said "it's probably just a problem with the baffling". I would let them check it out and they concluded the baffling was fine.

Even after the engine blew up and was replaced, it continued to have a problem with high CHTs.

It was so nice when I finally bough the Bonanza and my CHTs are consistently below 350.
 
Something is not right. I might suspect that people didn't follow normal break in procedures after the engine was rebuilt. Is it blowing through oil? Do you see full power, that is does it lift off where you'd expect? If you fly it, don't trust it. Not with those temps.
 
May not be broken in yet or was not broken in properly and cylinders are glazed. You could help it out by flying faster in the climb after clear obstacles but I would squawk it for that and see what they say.
 
A partially clogged injector would show up as a high EGT. EGT’s are all normal.
 
My 1 cent... I think the EGTs are a little low too... by about 200 degrees in climb and cruise... Slightly low EGT, slightly high CHT... maybe a timing issue? I also vote poor break-in possible, especially if they put the plane on the line immediately after the overhaul...
 
Mike Bush has a great youtube webinar on Cylinders. Above 400 CHT's, the structural integrity of the aluminum drops dramatically.


Fast forward to 29:28

Mike states never run a Lycoming cylinder above 440º and should be below 400º.
 
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Have a friend with a cooked #4 on his 172, o-360 and constant speed. He was flying it and it started running rough, noticed the last two flights #4 was a little higher than previous, 400++in climb, high time engine. He had never reached 400 on any previous flights on any cylinder.
 
EGT’s are not useful in actual values comparing between airframes. The values can be very different depending on probe placement. There are very useful for trends and proper leaning. In this case the OP said he was running full rich to cool the cylinders. If he has climbed a few thousand feet they are completely normal.
 
Your friends number 4 could be running hot for a number of reasons. He needs to have it looked at but there might be nothing wrong with the cylinder.
 
Jeff767 said:
Your friends number 4 could be running hot for a number of reasons. He needs to have it looked at but there might be nothing wrong with the cylinder.
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I should have also mentioned he and his mechanic pulled it, before pulling it compression was a little low with valve wobble out of spec's. Cylinder was toast.
 
JOhnH said:
Was that a joke?

Actually I had several A&Ps tell me the same thing when I complained about high CHT readings from my JPI 700 in my 172n. This was 10 years ago. I asked them how many 172s they worked on with multi cylinder engine analyzers. Most of them said "none" becasue 172's don't need them because they are bullet proof.

They were right. My 172 with high CHTs ran perfectly fine with those high CHTs, until the #4 cylilnder exploded in flight causing us to have to set down on a rather busy road at rush hour. Fortunately, no one was hurt. I never did find out WHY it always ran hot. I had several A&Ps check it out, including the "expert" at the engine shop that did the last rebuild on it. I told other A&Ps and they invariably said "it's probably just a problem with the baffling". I would let them check it out and they concluded the baffling was fine.

Even after the engine blew up and was replaced, it continued to have a problem with high CHTs.

It was so nice when I finally bough the Bonanza and my CHTs are consistently below 350.
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Nope, for example the Grumman AAx had not the best cooking, especially if no one installed a oil cooler on them, cessnas I haven’t had a issue with, even back in the drop zone days doing max climbs and max gross back to back. With good baffles and everything working the way it should in most places and for most missions cooling hasn’t really been a Cessna issue in my experience, now their door latch tech on the other hand lol
 
What was the oil level pre flight. I have a lot of time in r and s models and the only time they ran warm on CHT and not egt was when they were a tad low on oil.


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