sub-par oil pressure. ideas, please?

Folks, I'm getting ready for first flight, but it's on hold 'til I can work out an oil pressure glitch. I could use some more brains on this one.

Summary:
Pressure on startup goes to 45psi at 650rpm (great!). However, even with a full runup I don't get over 50psi.

System:
* Aero Sport Power (ASP) IO-360-M1B6 with Raven inverted system
* c/s prop
* standard oil pressure tap just inboard of top stbd engine mount
* steam gauge (temporarily teed in) corroborates AFS-2500 sensor
* straight 50 mineral oil
* ASP logs indicate 70psi during stand runs
* I haven't knowingly changed pressure relief valve (PRV) adjustment
* oil appears, smells normal (~25min total runtime). no debris when drained and examined.
* I pre-oiled engine prior to first start, injecting a few qt at top stbd fwd galley plug
* no leaks in system
* system quite full: up to 8qt on stick with inverted plumbing full and prop having been cycled
* all hoses eyeball- and hand-checked: no constrictions. All installed per Raven instructions

Symptoms:
* no-start cranking = 20psi
* 47psi @ 650rpm within ~1sec
* warms at seemingly normal rate
* constant 50psi at > ~800rpm (tested briefly to 2700 during prop bal)
* no change in psi as temperature rises
* prop cycles normally at > ~950rpm. temporary ~5psi drop when prop pulled back, with return to 50psi within seconds

So...any thoughts?

Here're mine:

* PRV maladjustment seems unlikely: ASP saw/adjusted to 70psi (adjustment to reduce pressure evident from lack of engine paint on ~2 threads of adjustment screw). why would it have changed? Aging spring possible; engine built 2004. Possible accidental adjustment? Would 2-3 threads account for 20psi? (rumor sez it's more like 3psi per turn)

* pump intake restriction seems unlikely: if present, I wouldn't think I'd see great pressure at idle

* others have noted oil pressure issues resulting from air leaks on the suction side (e.g. inverted system). I've not developed a clear picture of the expected symptoms in that case - can anyone provide some experience here? General principles lead me to think that a different set of symptoms would present for this case.

* air-locked or dirty PRV (per Lyco troubleshooting guide) seems like a good direction to explore, especially given that I pre-oiled via the galley and could have introoduced air or debris. Your thoughts? Can anyone explain exactly how the PRV can get air-locked?

Thanks for any input!

Adjust oil relief valve?

Alan,

Have you only just installed the raven inverted system? It is normal for the pressure to drop. Depending upon the lines you have installed (length, restrictions etc) the drop might be significant.

Things to check:
All fittings are tight and not leaking
Oil galley plug in the sump (behind the screen) is not loose
You could also have dirt/leak in the ball valve.

Other than that my logbook contains the following entry when I installed the Raven system:

Oil pressure relief valve adjusted 2 turns clockwise. Oil pressure in cruise increased to 70 psi.

Personally I wouldn't run an engine in with this setup installed. At a minimum remove the breather tank as the blowby back into the oil tank will just make things hotter and decrease performance. Your oil pressure will also be reduced and this is not a good time to have a sub optimum oil supply.

Remember as your oil heats up it will cool. I'd be looking for 80PSI cold as a minimum. The straight mineral oil is thick stuff. As adjusted from Mattituck I saw nearly 100PSI when cold. Once warm things settle down considerably. Also, you should have a new engine to 1000 RPM ASAP as most of them are lubricated by splashing. General theory is that less than 1000 RPM is not sufficent to keep all the parts lubricated.

Regards
Richard

oil pressure

If you run you oil pressure in the high 80's your engine will last a lot longer, especially if you do any acro. The Pitts/Christen system doers not maintain pressure in all attitudes. If you start out with pressure in the high 80's, momentary drops in oil pressure will be shorter in duration and recovery will be quicker. For non inverted aircraft the higher pressure helps with valve stem lubrication.
Cessna 172's built since the resumption of production take the oil pressure from the front of the oil gallery. The REAL pressure on these aircraft is ten pounds more than what the gauge reads.
I know of one IO 360 that was totally trashed in just 100 hours doing acro with low green oil pressure.

Alan,

Are you confidant the gauge is good? Maybe a trip to the auto store to get a "second oppinion" may be worth it. Then start with the easy and cheep, working to the hard and expensive. Pull and clean the PRV, something small may be keeping the ball from closing. Cheap and easy to check. Then start isolating portions of the inverted system. Run the line directly out of the bottom of the sump into the back of the sump direct to the oil pump. This eliminates all the rest of the inverted oil, and helps locate the problem. If you still have low pressure, you know it;s in the engine, if not, you know it is in the inverted system. Then start adding back components until you find the culpret.

Hope this helps.

Keep us posted on your results.

Chris

Thanks, all, for your input. Talked to Aero Sport Power today: they recommend the 'white spring' -- a higher-compression spring -- in the PRV for engines using inverted systems. I've got one on the way, Lycoming p/n 11713. They also recommend setting a somewhat higher pressure for inverted systems: 80psi @ 2400RPM, 190F.