Got rid of Shell multi-grade 1100 hours ago and never had another problem. Live in Texas, but have flown from Key West to Anchorage on Aeroshell 100. For me problem solved.
Hi Tom. Did you ever figure out the cause? I have the EXACT same problem. Start up and beginning of flight, OP is in the mid 80's. After take off, it slowly, but predictably starts to drop and by mid flight, it's in the mid 50-60psi range. If I fly hard (acro, full throttle), it drops much more quickly, but so far (until last weekend) has always stayed above 50psi, so I wasn't worried enough to stop flying. If I reduced power to 2100rpm or less, oil pressure quickly goes back up. Within about 5-10 seconds of reducing power, I'll gain 5psi or more. If I kept it reduced or pull back to idle (like going back to land), OP will continue going back up and by the time I land, I'm back in the 70psi range.
I have ruled out faulty sender, engine monitor, etc. Oil cooler was removed, and flushed. No obvious clogs or debris found. Vernatherm was removed and tested to be working. Hoses are clear, not kinked. Sump screen clean. Oil analysis has always come back good, but I did not do oil analysis the last two oil changes.
I have a fuel injected O320, slightly modified, FP prop, inverted oil and fuel. Oil is Phillips 66 100AW.
So what is it that would cause low oil pressure, but only at high throttle settings?? (or at least it's worse at high throttle settings and gets better with reduced throttle)
What make and type sump do you have?
My Titan IOX-370 cold air sump requires more oil than I was used to with my old standard Lyc sump O-360.
My "tell" was oil pressure would go up if I was pulling G. (forcing more oil to the pickup area). Apparently, it was the old soda straw in the empty cup syndrome.
In my experience a mismatch between case and oil pressure regulator housing will cause this odd behavior. The ball that regulates OP must float inside of a cage to work properly (keeps ball centered over flared hole in case). Old crankcases have the cage on the case and the newer ones have the cage on the housing and they accordingly have different housings to match. If you put the uncaged housing on the uncaged case, the ball will hold ok untill the volume goes way up at high power and then it falls off to the side and pressure drops accordingly as now it is bleeding too much oil off. Most A&Ps dont seem to know this. The 540 core that I bought was set up like that and struggled to understand why pressure dropped at high RPM, where it shouldn't. Mahlon pointed out this potential mismatch issue. He is a rock star! You will need to pull the regulator and see if there is a cage on the case. Mahlon has a post explaining the differences in looks of the two different housings- derby hat (cage on the case) vs abe lincoln hat (no cage on the case). The abe lincoln hat won't fit on a caged case, so if you have that style you don't have a mismatch IIRC.
Larry
Never saw an oil pump that was worn enough to cause any problems pressure at RPM. sometime a little low at low rpms but never any issues at high rpms. They can be really messed up from camshafts going bad and you never see any issues with oil pressure at rpm. I would totally discount a worn pump.
If it were me, I would get a hold of a normal oil pick up screen and cap and install them and plug off the raven three way valve and fly it as a normal non acro engine to eliminate the entire acro system. To me, you need to determine if the problem is the Raven system or the engine first, before pursuing anything else.
I assume that you have confirmed that the oil pressure is doing what you say with a direct reding gauge as well.
Good Luck,
Mahlon
1flyingyogi, what kind of propeller do you have, a standard CS or an aerobatic counter-weight type?
I spoke too soon.
Yesterday, I only did a taxi & runup with the cowling off. OP was good.
Todays test flight at startup & various throttle settings
OP-OT-RPM
62-104-1050 at startup to taxi
74-129-2270 in flight
71-168-2510
65-188-2240
41-192-1130 landed & taxi back
CHTs 363,364,364,365 in flight
EGTs 1370-1397
I'm draining the oil & will check the suction screen next.
Question regarding the pressure relief spring.
Do the springs lose tension & have to adjusted over time?
Any other suggestions appreciated.
Note:I'll be downloading the data later today.