Question for Paul McBride, the General Aviation News engines expert: I have developed a high oil temperature issue in my 1969 Mooney M20. I have replaced the vernatherm oil cooler, but no improvement. The next step was to remove the oil filter adapter and inspect. I have also replaced the oil temperature probe.
I have thrown time and money at this with a mechanic and so far can’t seem to make improvements.
Oil pressure remains good throughout.
Any suggestions?
Peter
Paul’s Answer: Something to keep in mind is that this very well may be related to the age of the aircraft.
If possible, try to get a gauge and sender unit you know is accurate, which will allow you to remotely check and entirely discount the aircraft system. This should be a simple first step in troubleshooting the system.
From the information you provided, I’m honestly not certain that you have a problem with high oil temperature rather than an instrument or wiring problem.
What makes me lean this way is because of your statement regarding the oil pressure.
From my experience, if the oil temperature is high, we expect the oil pressure to be lower, and apparently this is not the case with your Mooney.
I’d like to recommend that you also check the oil temperature sending unit for proper function. If possible, check the entire wiring of the oil temperature gauge, because it could possibly have a frayed wire that would cause the gauge to be grounded and show an incorrect measurement.
I’d also recommend you review and comply with Lycoming Service Instruction 1316A just to be sure that the seating surface of the vernatherm and the corresponding seat on the oil filter adapter and/or accessory housing, if you don’t have an oil filter, are seating a full 360°.
This may seem like something simple, but in a tightly cowled installation such as the Mooney has, this becomes very important.
Once the Service Instruction is complied with, you must install a new vernatherm because a previously used one probably has already established its wear pattern and won’t be compatible with the new surface provided by the reamer mentioned in Service Instruction 1316A.
The only other thing that I can think of regarding this type of situation is an article I wrote back in July 2014 mentioning the use of a glass bulb thermometer to check engine oil temperature (Ask Paul: Tips to troubleshoot high oil temps.)
I seriously doubt that oil temperature is the problem here, so that article may be of some help also.
Instead of using a glass thermometer I use a digital meat themometer on a braided wire. No worries of breaking it and it gives you an immediate digital reading.
I had a similar problem with a new engine. I finally got Lycoming to inspect the engine after a year and a half of complaining. They found two issues. A bad gasket (thread) between the engine shells and a cracked exhaust ring.