M20K 252 Oil pressure question

[tpreece]

I just picked up my 252 last week after a complete overhaul from a very reputable engine shop. The maintenance shop that installed the engine, ground ran it several times and even flew it before I picked it up and flew it 3 hours home. On the flight home the oil pressure was between 46-50PSI the whole trip with just under 8 qts of oil before I left. After I landed and taxied in it was around 30PSI with the oil at temp and low power setting. I went to fly it this evening with about 7 quarts and oil pressure was about 80psi on start up (45F OAT). Everything was normal up until I leveled off at 5500 feet and set cruise power(28" 2500rpm), oil pressure was down to 35 PSI but stable. Oil temp was pretty cool at about 134-140f. Oil temp is colder than I would like but this is normal based off my 3 hour flight home. The PSI obviously caught my attention since it was quite a bit lower than it was the last flight just 6 days ago. Taxiing in the oil pressure came all the way down to 12psi so something is not right. My first thought is that after startup something came loose and is causing a leak. I am going to de-cowl and have a mechanic look it over before the next flight. Any thoughts or suggestions are much appreciated

Edited March 10, 2022 by tpreece

[LANCECASPER]

What does your POH say is normal operating oil pressure, minimum idle oil pressure and maximum oil pressure?

I had an M20K Encore which has the -SB engine, here’s what the POH said:

 

 

if your POH says the same, then you’re probably good. If they think it should be adjusted, it’s not too tough to do.

[tpreece]

Mine is the same at the above, technically it was in the okay range but with a change that dramatic from the last time I flew it something in the engine has changed which is where my concern lies

[smwash02]

When chasing some MP issues in climb, main turbo told me the -SB waste gate needs 52 PSI. 

Based on that I would think you'd want to increase it, but I'm not an A&P. 

At 130-140F I think my oil pressure would be in the 60s-70s. 

[Ethan]

TPreece,

I have an 1981 Mooney 231 with an LB engine. Since having my engine factory remanufactured in late 2018 my engine behaves the same way. It starts out with good strong oil pressure, then as it gets hotter, the oil pressure drops to the low green. At idle, oil pressure is in the high yellow range. I asked me mechanic about it and he shrugged his shoulders. The engine runs well and 650 hours later I have just gotten used to it.

 

Ethan

[ToddCC22]

Might be worth a check for water in the oil while the cowl is off. I would think it would be the first thing out of the quick drain if there is any. If oil temp isn’t  getting high enough in flight, condensation doesn’t get removed and the oil/water mix can reduce pressure. Just an uneducated thought…….

[A64Pilot]

Excess water in oil will make a chocolate milkshake, the water emulsifies in the oil. it won’t stay separate.

Before I did anything to the engine, I’d verify the accuracy of the gauge

Edited March 11, 2022 by A64Pilot

[Hugemiester]

What did the engine shop that just worked on it have to say? That would be my first call? Having another mechanic get involved a week or so later seems odd. If your shop is reputable, they should also be concerned. Good Luck!