Question for Paul McBride, the General Aviation News engines expert: Checking with you about CHTs on Cylinders 5 and 6 reaching 445° on climb and cooling to about 400° after power reduction in cruise. This is in our Piper PA-24 Comanche 260B.
I own an aviation company that provides chase services for drones in Southern California and the rest of my fleet are powered by Continentals.
The young commercial pilots think this means the engine is running hot and they call it a ticking time bomb.
I want to instruct the staff that these CHTs are acceptable and to continue to monitor them during the chase mission.
The engine has 1,890 time SMOH, but otherwise runs well. We did check the baffling and I think our mechanic made an adjustment to the back baffling.
Any advice? Thanks.
Julie Mangold, via email
Paul’s Answer: Julie, your question is one that comes up quite frequently and could possibly have many answers. I’d like to approach your situation from the simple perspective that there really may not be a problem at all.
First of all, I’m assuming that your PA-24 Piper Comanche 260B is powered by the Lycoming IO-540-D4A5. The operator’s manual for that engine clearly states that the maximum CHT is 500° F and for extended cylinder life, the engine should be operated somewhere in the 400° to 435° range.
According to the information you provided, your engine is operating as it should and is within the recommended specification.
I’d suggest that the pilots who are questioning the figures might do well to refresh their memories by referring to the engine operator’s manual and the published data.
Just in case there is not an operator’s manual available, you might consider ordering one through your local Lycoming distributor or directly from the factory. The specific part number for this manual is 60297-10.
Now, I’d like to expand a little regarding this issue.
I’m certain, if you’ve read any of my past articles relating to cylinder head temperatures, you will know my deep concern for aging aircraft and the accuracy of their instruments. Instruments on aging aircraft are known to be out of calibration and unreliable.
You indicated that the maintenance staff has already checked the baffling which, as you know, is a big factor concerning CHTs. Even though the readings you mentioned are well within specifications, if possible, I’d confirm those readings with a known good, calibrated instrument.
Again, I don’t think you’ve got any serious issues with the CHT temperatures and doing a few simple things to check the accuracy of the gauge and educate the pilots about monitoring the gauges and the operating parameters should serve you well.
I must say that having 1,890 hours total time on an overhauled engine tells me that you’ve been doing something right all along.
Keep up the great job and remember frequent oil and filter changes are key to keeping the engine running at its best.
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