Oil Temp Troubles

[M20Kid]

I'm new to Mooney ownership having purchase a 1981 M20K-231 just a couple of months ago.  My airplane is a much fun as I always imagined it would be in a Mooney but I'm having a problem that I'm hoping others have seen before.  My airplane has the -LB upgrade with a Merlin Wastegate but no intercooler.

According to my JPI scanner, the CHTs on all cylinders is running in the 375 range in cruise with the cowl flaps closed but the oil temp, on the factory installed gauge, is running about 220 and the oil pressure is dropping to the bottom of the green arc.  By trailing the cowl flaps (and giving up about 5 knots) I can bring the oil temp and pressure the to center of their respective gauges and all the CHTs drop to about 325.  I've had a mechanic put a certified gauge in the oil pressure line to verify the gauge accuracy but I haven't done that with the oil temp.

On a mechanics advice I've replaced the oil cooler and vernatherm without any noticable change.  I don't want to keep throwing cash at the airplane to see what works.  My question is, would an intercooler help with my particular issue?  Would anything else help or is this just the way this particular airplane operates?

Thanks in advance for all the input!

[Piloto]

An intercooler will not help you on this. How old is the oil and what level you have? You can lower the temps (30F) by adjusting the cowl flaps rod ends to keep them open 1/4" to 1/2" when the control knob is fully inserted. This will not affect your speed. A low oil pressure (at low RPM) is usually an indication of bearings wear. How many hours on the engine?

José

[DonMuncy]

On the Continental engine, contrary to Lycoming (and virtually every other engine anywhere), the oil pressure sensor is "down-stream" of the flow to all the necessary lubrication points in the engine. It is therefore reading the pressure that is left over after it does its work. Because of this, Continental oil pressures are always lower than other engines, especially when hot. As long as the oil pressure is in the green, you are unlikely to have any problem.

[xftrplt]

Don, interesting info re the pressure pickup location.  As I'm sure you know, the oil pressure is adjustable via a screw on the oil pressure relief valve.  I had it tweaked up on my 231.  It's a simple (cheap) procedure.

[DonMuncy]

Thanks for the reminder Dick. One just needs to be careful they don't get the pressure too high when cold, trying to get it high enough when hot. I don't have any real knowledge on it, but it would appear that if you set it at during the summer, when really cold weather hits, it may go over the top limit.

[xftrplt]

Quote: DonMuncy

Thanks for the reminder Dick. One just needs to be careful they don't get the pressure too high when cold, trying to get it high enough when hot. I don't have any real knowledge on it, but it would appear that if you set it at during the summer, when really cold weather hits, it may go over the top limit.

[M20Kid]

Thank you for the great information, I was unaware of the sensor location on this engine.  I did have the oil pressure tweeked up a bit within a few days of buying the airplane but it seemed to have very little affect on the oil pressure when hot.  It did raise the cold pressure, though, and it hits the high end of the gauge right after starting.  According to the Continental tech I spoke with, this high pressure during start is acceptable as long as it comes down and the engine isn't run hard until the pressure begins to drop.

One thing I found the other day (unsubstantiated at this time) is that Mooney oil temp gauges are not linear!  The person I was speaking to told me Mooney knew they had difficulty keeping the temp down and so they adjusted the gauge so it would show the majority of the temp change at the start of the gauge and then slow down at the top.  This would make the gauge show the last 30 degrees, or so, as perhaps the last 1/3 of the gauge!  He said that's why the numbers are only at the top and bottom of the gauge (100F and 240F); the gauge only needs to be accurate at marked temps and can show anywhere on the gauge as long as it's between the numbers!  He suggested installing digital oil temp/pressure gauges to get a clear picture of what's going on.  Any thoughts on this??

I do use AeroShell 100W (straight 50 weight oil) because I live in the AZ desert.