The O360 in my Patrol (fixed pitch prop) had no baffling around the front of the crankcase, so cooling air was entering at the front and diving down to exit below the engine before it had done any cooling work. The result was CHTs around 450 dF on climb out. Although this is below redline for Lycoming, it is well above what is best for engine longevity. The definition of max CHT is set by the FAA to be the highest temperature the factory could get without detonation or pre-ignition. So this has nothing to do with longevity. For Lycoming it is wise to set redline CHT at around 420 dF. For Continental it is about 400dF. (The metal and structure differs between the 2 engines.)
So now I have aluminum baffling very similar to the photos in this string. The rule of thumb is that the total of all leakage should be no more than roughly the size of an American quarter dollar coin. With the new baffling, my CHTs dropped by at least 30dF. I don't know why the original builder didn't baffle this area at all, cos it is huge air escaping. He did not have an engine monitor, so he would not have known the CHTs. I bought it with 70 hours, and he had only been pottering around the pattern, so I think the engine is still healthy. All the usual measures of engine health are really good - oil consumption, boroscope images, compression numbers, flight performance, etc.
What are my credentials for making these declarative statements? Two decades of very deep study (as a Mechanical Engineer) prompted by my Bonanza engine, which has had "problems". The Gurus on this subject are Mike Busch and the engine factory Gurus who present every year at Airventure Oshkosh. Oh, and never fly without an engine monitor! The JPI EDM 830 is an excellent choice, and factory support is very good.
Jim Herd
Minden, Nevada
