Strange EGT and CHT

Your temps may being influenced by your prop pitch vs the rpm and throttle position. You may be causing the engine stress just like when people over pitch the prop. This will cause increased fuel usage and higher engine temps.

It won't hurt to try a different prop pitch setting with a different rpm and see if it makes a difference.

Hi Roger,

I would have thought that too, but my prop was at full fine (pitched for 5700 WOT) and I had backed off to about 4800 rpm, and slowing down.

I can't work it out!  Why would an increase in throttle lower the EGT?  Sounds counter intuitive to me.

Because when you were advancing the throttle you were enriching the fuel flow at the higher rpms. Getting down into the mid 4K's leans it out.

Ahh.. Ok.  Thanks for the info.  Not much I can do when at full fine, unless I leave it coursed up a bit when I back off, but that is probably not healthy either.

John,

This is a typical misconception.  Pilots often make the mistake of thinking they can lower EGT by reducing power.  However as you reduce power you are unloading the engine and EGT can rise. While it is true that advancing the throttle provides a richer mixture thus lowering EGT, there is something else at work here also.

Think of EGT and CHT as opposing forces. CHT represents engine load producing thrust, EGT represents wasted heat out the exhaust.  If you pay attention you notice an inverse relationship. For a given power setting, loading the engine heavier will increase CHT, while EGT will fall.  Unload the engine and EGT will rise while CHT will fall.  What you are experiencing is exactly as expected.  Loaded engine = more wast heat goes into the heads, unloaded engine = more waste heat goes out the exhaust.  

Remember, CHT represents engine stress, EGT does not.  EGT is simply a measurement of combustion energy being wasted out the exhaust. This is more apparent on our aircraft since we cannot adjust the mixture to compensate.  You might try initially decreasing throttle with the prop left in cruise position, and go to the fine pitch in the pattern to prepare for a possible go-around.