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Rise in oil pressure at low rpm

morsesc

Active Member
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.
 
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.
 
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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?
 
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.
 
Strange Oil Pressure Readings

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.
 
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