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What, Ideally, should my hottest cylinder, in cruise, be about in degrees ?

The Kid

Thompson Falls
EGTs are way hotter than CHTs and other than they drive up the CHTs, maybe don't really mean that much? But too high of CHTs may get you a burned exhaust valve. So, ideally, what temp should I strive for in in cruise on my hottest cylinder? I've been striving for a combined EGT/CHT of not over 1700. But the CHT is really the one to watch and try to get in that sweet spot. So, again, what degrees should I strive for on my CHT?
My goal is 375° in cruise. I’m as concerned with low temps as high and I want all cylinders to be close in temps throughout the range of ops. My Cub runs around 335° if I don’t lean aggressively. My 180 required effort to get below 400°.
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EGT’s are extremely sensitive to probe placement. If one probe is 1/8” further or closer to the exhaust valve you will see a huge difference in temp. EGT is useful info for leaning the mixture and may be an early indicator of a cylinder problem. That is about all. CHT is everything. As Stewart says too hot or too cool is bad. 350 to 375 in cruise is good. If they go over 400 in a long climb that is generally ok and normal but I would get nervous if they get over 425 or so. Max is 500 on Lycoming.
If 90% of your flight time sees CHT’s below 400 you should be fine. An occasional excursion above 400 up to 425 or so is not going to significantly reduce the longevity of the engine. If you are above 400 in stable cruise flight you probably need to try to get them into the 350 to 375 range.

my humble opinion

hope it helps

In the Cub I try to keep my CHT'S below 350 for cruise. I lean aggressively and usually can keep the temps in the 330 range, they usually run even 15-20 degree cooler with a real flat prop. I blend my fuel so I run about 1/4 of the lead that 100LL has. In a hard full throttle climb #1 and#2 will get to 400 but back down easily when I level out. In my mind avoiding the excess heat help with early valve guide wear, leaning and lead management helps with avoiding stuck valves. The Cessna 180 has a carb and CHT'S are spread out a lot more then the cub. Normal Cruise CHT temps are around 360 on floats some will get over 400 but have improved with adding gills/exhaust fairing. Look up the manual for your engine I seem to remember that some have made changes to the standard oncoming recommendations of usually lower temps. Advanced timing/high compression pistons/poor cowling design/improper mixture all can cause high CHT's
It is interesting to me that in bygone days you really had no idea what cht or egt was, but now we are hyper focused on it. Of course engines were cheaper and more readily available then.

I used to target 350 in the 180 but am finding 375 to be its new happy place with reasonable fuel burns. In high ambient temps, it’s harder to do. We have had a hot summer.

Mike Busch said:
The best proxy we have in the cockpit for exhaust valve temperature is cylinder head temperature. (Note that it isn’t EGT.) Most of us know that it’s important not to let CHT get too high for optimal engine longevity. I’ve long recommended keeping CHT no higher than 400 degrees F for Continentals and 420 degrees F for Lycomings, with CHTs about 20 degrees F lower than those maximum temperatures being just about ideal. We keep our CHTs below those maximums mainly by using the mixture control properly and operating either enough lean of peak or enough rich of peak to prevent excessive CHTs.But some pilots seem to think that if a little CHT reduction is good, then a lot of CHT reduction must be better. That’s not the case, and now you know why. Excessively cool CHTs mean low combustion temperatures that slow the lead scavenging process, and cool exhaust valve stems that promote lead oxybromide deposits.To minimize valve sticking (especially in Lycomings), it’s important to try to keep CHTs in “the sweet spot” between 350 degrees F and 400 degrees F as much as possible. It’s also important to lean aggressively during taxi and other low-power ground operations to keep combustion temperatures as high as possible.
From everyone's favorite maintenance pundit, Mike Busch. https://www.aopa.org/news-and-media/all-news/2020/july/pilot/savvy-maintance-valves
Great information from Mike Bush, I feel much better about my Lycoming CHT's after that read. Learned something new today, thank you Narwhal!