What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Low oil pressure

rv4dude17

Well Known Member
UNRESOLVED as of 7/13/20—-My rv4 engine (0-360 a1a) is reading low oil pressure on the grt eis.
It was showing a healthy 75 psi while flying, then it went to 30
Then 20 psi. I landed no problem.
Where do I start looking for the problem?
SD
 
Last edited:
If a VDO sender is used, they tend to go off scale high when the wiper inside wears or the ground goes bad or fails.

A new sender is usually good to have.

A direct reading gauge run to the cockpit temporarily helps troubleshoot. $15 @ a auto store. If you have an oil pressure manifold with a hobbs switch, maybe temp install it there.

Low oil pressure confirmed- trash in the oil pressure regulator seat or clogging sump screen are most common if not just a sender issue.

A greatly timed end of flight if a true engine internal issue.

Do you have an external ground to your engine side of the forest of grounding tabs from the oil pressure sender?

They seem to last 300 hours or so for many here.

Not an expert, just a first stop vs searching threads until others help more. A primer - https://www.kitplanes.com/maintenance-matters-48/
 
Last edited:
Oil pressure test kit from Harbor Freight

I had the same problem a couple months back.. bought an oil pressure test kit from Harbor Freight (spruce was selling the same kit for $43 vs $29)
I needed a different fitting but happened to have one on hand. Ran into the cockpit and ground run verified the engine was producing great, fantastic, fabulous oil pressure of around 78 lbs. Replaced the sender and am back in business.

https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html
 
I installed a mechanical gauge

I have done several things to no avail. I first removed the oil bypass to make sure that there wasn’t anything between the ball bearing and seat- clean. Then I cut open the oil filter to be sure there was no metal indicating shredded gears -clean.
Then I installed a mechanical oil pressure gauge. When I started the engine, the oil psi was around 55, so I thought it was resolved. When full power was applied for takeoff and about 20 feet AGL the oil pressure went back to 20. I landed immediately. But once on the ground and at idle, the oil pressure went back to 55. I’m baffled.

SD
 
I have done several things to no avail. I first removed the oil bypass to make sure that there wasn’t anything between the ball bearing and seat- clean. Then I cut open the oil filter to be sure there was no metal indicating shredded gears -clean.
Then I installed a mechanical oil pressure gauge. When I started the engine, the oil psi was around 55, so I thought it was resolved. When full power was applied for takeoff and about 20 feet AGL the oil pressure went back to 20. I landed immediately. But once on the ground and at idle, the oil pressure went back to 55. I’m baffled.

SD

assuming these readings were from the mechanical gauge. I would pull the strainer. increasing RPM means increased flow through the oil pump. That could be sucking some trash (like a rag) into the strainer cavity ports, partially choking the flow and resultant pressure drop. Lower RPM (i.e. idle) means lower flow and not as much suction to hold the trash against the strainer inlet ports. The oil pump is constant displacement, which means oil flow is linear with RPM. A very low oil level will give similar symptoms, as would a crack in the casting that forms the suction tube in the sump. Older engines had a separate suction tube and this could come loose, giving similar symptoms.

Could also be the wrong oil pressure relief cap. There are two types (for blocks with cage adn those without) My 540 core that I bought had the wrong one installed and my pressure would decrease with increasing RPM, at a certain RPM level. At a certain point, the ball comes completely off the taperred face as flow increase (when no cage is present) and slips to the side. The moment this happens, the pressure drops. It then goes from increasing pressure to decreasing pressure as RPMs rise.

The derby hat styles goes with a caged block and the abe lincoln hat style goes with the un-caged block. The cage, if it exists, extends out of the block to contain the ball as it comes of the seat. The abe lincoln style cap has the cage built itno it, instead of the block. This type won't go onto a block with a cage, but the derby style will fit onto a block without a cage and give the symptoms I described above. That said, I never saw pressure below 50, so feel that blockage is more likely.

Larry
 
Last edited:
Check the suction screen! If you have inverted oil, check the suction side hoses for internal collapse.
 
Back
Top