C172SP High Oil and CHT Temps

[Kenny Taylor]

I flew a local C172SP rental this weekend and noticed it developed a tendency to overheat. I've flown this plane many times over the last 18 months, and it's never overheated previously despite hot summer days and constant Vy climbs.

The attached pics were taken climbing out of 4,000 feet on the coast. We were climbing 500 fpm, a bit rich of peak, around 90 KIAS, with an OAT of 78-80 F, and about 250 lbs below gross weight. After seeing the indication, we leveled out and allowed it to cool until CHTs were all in the green and oil temp was between 210-215. We had to keep the climb rate below 300 fpm to keep it out of the red after that.

I brought it up with the plane's owner, who seemed to disregard it as "way low" oil. We measured 6 qts at takeoff. It seems there are a lot of opinions on what "full" is, but 6 qts is not terribly low, and something else had to be going on.

I can't remember where "normal" was previously, other than being nowhere near redline. What does normal oil temp and CHT look like on the C172SP?

 

[Dan Thomas]

A "bit rich of peak" is a hot place to be. This is what the airplane's AFM says. You have one, right?



So what do the temps look like if you lean it to max RPM in the climb?

 

[Skip Miller]

Is the engine carbureted or injected? Were you climbing at wide open throttle? I don’t know about the 172S, but many older Cessnas had a fuel enrichment circuit that would add fuel to the mix when at WOT to help temps remain in the green, at full throttle. Carbureted engines only, obviously.

Listen to @Dan Thomas he knows this stuff!

-Skip Miller

 

[Kenny Taylor]

Affirm on the POH. I went back digging into it.

@Skip This one is fuel injected.

 

[idahoflier]

The POH onboard the aircraft should tell you what the normal Oil and CHT temps should be. 476°F is way too high. While Lycoming has redline at 500°F in the Operator's Manual, it also says "For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation. The max Oil Temp is listed as 245°F.

As a general rule I always climb my O-360 powered C172N full rich to keep the CHT below 400°F...

 

[Dan Thomas]

Is the engine carbureted or injected? Were you climbing at wide open throttle? I don’t know about the 172S, but many older Cessnas had a fuel enrichment circuit that would add fuel to the mix when at WOT to help temps remain in the green, at full throttle. Carbureted engines only, obviously.

All 172s/182s/206s built from '96 on are injected. That covers the 172R & S/SP models.

Listen to @Dan Thomas he knows this stuff!

Some stuff. Not nearly enough. You will note that I seldom say anything on things like IFR piloting, for instance. My IFR rating lapsed (as Canadian IFR ratings do) 24 years ago. Instructor rating lapsed at least 16 years ago. Things have changed some in the meantime.

You'll also note that I usually refer questions back to the POH/AFM, parts manuals, service manuals, engine manuals and so on. Those are authoritative documents that trump the opinions of most of us. Experience covers much, but documentation is better. The key to "knowing" stuff is mostly knowing where to find that stuff. I'm a bit of an information junkie, so finding my way around the web comes more easily.

 

[Hang 4]

Did temps get more normal once you leveled off?
Did you try richening the mixture?

That's seriously hot. I would not fly that plane until the cause was understood.

 

[Dan Thomas]

As a general rule I always climb my O-360 powered C172N full rich to keep the CHT below 400°F...

But as you climb that mix gets richer and richer as the air density decreases, and the engine will start to run rough and lose power. The POH has things to say about that.

We had a student call us from a distant airport. He had taken off in the R182 and when climbing the engine was running rough and looking back out of the rear window he could see black smoke trailing behind the airplane. He had returned to the departure airport. I had an AME check the engine just in case, but nothing unusual was noted. I asked the student how high he was when the airplane was shaking and smoking, and he said 7000 feet. "And where was the mixture set?" Full rich, it was. Well, of course an R182 will do that. It has the HA-6 carb that runs very rich at full rich, as requested by Lycoming to Precision Airmotive, the carb maker. One has to check the POH. That's what it's there for. And this is what it says:



The student's POH knowledge had somehow been overlooked. We were pretty strict on that.

The R182 would run rough even at more normal altitudes with the carb heat on. The students and instructors were forever complaining about it, and I was forever reminding them that it was perfectly acceptable to lean the engine with the carb heat on, and smooth it out. And it was also often necessary to lean it in the runup to get acceptable mag drops. That HA-6 carb is a pain.

 

[Kenny Taylor]

Did temps get more normal once you leveled off?
Did you try richening the mixture?

That's seriously hot. I would not fly that plane until the cause was understood.

Oil temp dropped to between 210-215 on level cruise, which still seemed high. CHTs remained in the green but barely. Probably in the 440-460 range. Richening the mixture helped slightly on climb, but not nearly enough.

 

[Dan Thomas]

Oil temp dropped to between 210-215 on level cruise, which still seemed high. CHTs remained in the green but barely. Probably in the 440-460 range. Richening the mixture helped slightly on climb, but not nearly enough.

That engine might need some work on its baffling. It doesn't take much of a leak to push the CHTs and oil temps up.

 

[idahoflier]

But as you climb that mix gets richer and richer as the air density decreases, and the engine will start to run rough and lose power. The POH has things to say about that.

While that is true, I will sacrifice performance to keep the cylinders cool. I haven't noticed any rough running issues and I deal with climbs to a DA between 10K-12K. On summer days if I lean in the climb my CHT's will easily climb above 400°F in short order. I was referencing my particular aircraft, a C172N with an O-360. Since the OP was flying a C172SP with an IO-360 it's not a direct comparison, and it was not my intent to imply the OP needs to climb full rich for his aircraft. I was just trying to convey what I have to do to keep CHT's below 400°F.

All that said, it sounds like it's a rental and below 500°F, so full send I guess! ;-)

 

[23103a]

Are you sure you were really rich of peak? 10.6 GPH and 1450 EGTs would suggest you're a lot leaner than that...?