Small Oil Pressure Fluctuation – Advice?

[Clipper Driver]

Recently, I noticed a very slight periodic fluctuation in oil pressure for the O-235 in my Piper Clipper. The airplane had just come out of annual, and an oil change and filter check during annual showed no metal or problems. In the two years I’ve owned the plane, the oil pressure has been at or just below the bottom of the green arc when the engine is up to operating temperature (see photo). In the last month or so, the oil pressure will drop maybe 5 psi for 30 seconds or so (rough guess of 60 psi), then go back a position at or just below the bottom of the green arc. In a few minutes, it may do it again. The needle doesn’t pulse or vibrate, and the pressure doesn’t change abruptly. I mentioned it to the AI who did the annual and who has maintained the plane for the last five years or so, and he says there is no cause for immediate concern, but to keep an eye on the oil pressure and get back to him if it continues to drop.

Should I be concerned about this, and/or does anyone have any advice regarding the possible cause(s) and what I might do to find the cause?

Other relevant info:

- The engine has about 750 hrs SMOH, but the overhaul was done long ago. It runs well. Oil consumption is currently about 1 quart in 8 hours, but has been higher at times – maybe 1 quart in 6 hours.

- The oil pressure is highly temperature and RPM dependant. At full power on takeoff with the temperature at the bottom of the green arc, the oil pressure will be at the top of the green arc. As the engine warms up in cruise, the oil pressure will slowly drop to the bottom of the green arc. At 1000 RPM idle, just after starting and before the engine comes up to temp, the oil pressure will be in the middle of the green arc. Just after landing with the engine at operating temperature, the oil pressure will drop to halfway between redline and 50 psi at 1000 RPM – maybe 35 psi. If the engine is hot and idling at about 700 RPM, the oil pressure will be at redline. From what I’ve read and heard, this is normal, and I do not need to be concerned about low oil pressure at low RPM when the engine is hot.

- I installed a Hobbs Meter with oil pressure switch last year. We tried to make sure no air got in the line, but there is the possibility some air got in and made its way to the oil pressure gauge. Opinion of some is I ought to suspect the gauge rather than the engine.

I plan to fly the plane conservatively (fly higher, close to home, and in the vicinity of airports) until the situation stabilizes. If it gets worse, I guess it will go to the shop for further diagnosis.

Thanks in advance for any advice.

 

[51-pa22]

and your running what type of oil ? AeroShell W100 Plus???

Seems JohnW or Steve will answer but just for FWI what type of oil pressure relief valve are you using the adjustable type of fixed?

 

[Clipper Driver]

and your running what type of oil ? AeroShell W100 Plus???

Seems JohnW or Steve will answer but just for FWI what type of oil pressure relief valve are you using the adjustable type of fixed?

I use AeroShell W100 Plus most of the year, and Aeroshell W 15 W 50 in the winter (although I stayed with W100 Plus last winter - it was fine and no starting problems as I don't fly when it's really cold).

The engine is an O-235 C-1. I haven't done anything with the relief valve, but I'm pretty sure it is the fixed type. Awhile back, the AI said he could add some washers to increase pressure if I wanted, but I declined. Sort of glad I didn't because if adding a washer would make a lot of difference, I think the pressure would be too high when the engine is cold.


Thanks,

 

[NHPacerPilot]

When I had my old O-290-D (1951) it was doing the same thing when I tried the multi viscosity oil. It to had about 750 hours and had been field overhauled years ago. I used Aeroshell 80 on the winter and 100 in the summer. On three seperate occassions over the years that I(over 11 years) had the engine, I tried X-Country 20W-50 at the urging of different mechanics. All three times, the OP would start fluctuating downward and back up and then down again after only an hour or so of flying. The first time I turned around and landed and no one could explain what was going on. We tried adjusting the PRV and could not get it to stabilize. I read from an old timer that the old engines just wanted to use the single weight oil and once they were used to it, they did not want to use anything else. My mechanics told me I was crazy and they never heard of such a thing! All three times, within a couple of hours, I drained the multi-weight and put in the single back in. Bingo it ran just fine and was stable. Once the mechanic did not tell me he put in the multi-weight and I flew away only to have the OP start acting up. I landed and knew before I looked at the log what had happened and sure enough I had to change the oil. The mechanic grumbled but paid me for the oil since he put in what he wanted and not what the engine wanted. This might not be your problem, but I was religious about using the summer weight and the winter weight singe grade oil and never had another OP pressure problem again. In that engine anyway. My new O-320 is another story altogether! LOL