Rise in oil pressure at low rpm

morsesc · #1 12-08-2015, 04:06 PM

My oil pressure is normal at startup, run up and while flying. I noticed that after flying when I pull up to the ramp and lower the rpm's, oil pressure begins to drop as it should then at about 2100 rpm the oil pressure begins to rise. As I lower the rpm to 1800, oil pressure will rise to about 50psi before slowly settling back down to mid 40's. I have cross checked with a manual oil gauge so I have eliminated that as a fault. I also have the mushroom style oil pressure relief gadget. Oil pressure is always in the green but having it rise at idle is a mystery. Also, since it only does this after taxiing back to the ramp, it may have been going on for a while and just didn't notice. Any ideas or thoughts would be appreciated.

Pat Stewart · #2 12-08-2015, 04:20 PM

Mine just bounces rapidly between 48 and 53

morsesc · #3 12-08-2015, 04:41 PM

Hi Pat. Have you moved the sender away from the engine and do you have the newer style pressure relief valve? Mine was like that until I did those two mods. If, however, it never varies from this 48 to 53 psi at all, something else is going on.

morsesc · #4 12-09-2015, 01:23 PM

I hate answering my own posts but a friend of mine who owns a SportCruiser tested his engine and said it's doing the same thing. Maybe the oil pressure relief valve closing at low rpm's and giving a rise in oil pressure?

Sink · #5 12-11-2015, 06:47 AM

Each engine is a little different, but the pressure could change by 10 psi from a very low idle to cruise rpms. Oil brands can also play a small factor here. The pressures differences can be from a poor ground, air in the line, a sender not operating at 100% (many don't), or if you have the ball bearing versus the mushroom style oil pressure regulator. Even having it on the engine versus a remote mount can make a difference.

RV3bpilot · #6 12-11-2015, 07:51 AM

My sender unit went bad and before it died completely it gave very strange readings, once it was very high and then very low... I replaced the sender and gauge with a simple old style pressure gauge with a copper line going through the fire wall.
I do not connect the copper tube to the engine because it moves to much and will destroy the copper tube. I take the oil pressure from the top of the oil filter that is mounted on the firewall.
If you take the oil pressure from the engine use a plastic hose after you go through the firewall. The plastic hose must be protected from heat with fire sleeve.