Low oil pressure at high power

Flew an RV-12 today and had a strange problem. Wondering if anybody else has seen this. At high power, the oil pressure dropped. It was hanging in the mid 20's, but then when it dropped below 20 we landed short of our destination. When we pulled power, pressure started climbing. By the time we were on the ground it was up over 40. We changed the oil and put in Mobile 1 Racing 4T and tested. It dropped to 29 on our claim out so we pulled back and limped home at 4300rpm and the oil pressure maintained 30-32psi. Landed and it was back up to high 40's. Has anybody seen this?

We are thinking the oil pressure regulator is the old style and plan to change that first, but any other thoughts?

Thanks in advance.

Below are links to automotive forums with similar symptoms.
A possible cause could be a restriction in the oil inlet to the oil pump, either in the oil tank or oil cooler or hoses.
Grass Roots Motor Sports
Oil pressure goes down when RPM goes up
Piston Heads
Hot Rod

Saw this once

Jesse,
I found a loose ground but changed the sender anyway. Fixed problem. Assuming the gauge, wiring, and sender is spot on accurate at all phases of operation, then oiling issues like what was mention above or possible bearing wear.

Jesse said:

Flew an RV-12 today and had a strange problem. Wondering if anybody else has seen this. At high power, the oil pressure dropped. It was hanging in the mid 20's, but then when it dropped below 20 we landed short of our destination. When we pulled power, pressure started climbing. By the time we were on the ground it was up over 40. We changed the oil and put in Mobile 1 Racing 4T and tested. It dropped to 29 on our claim out so we pulled back and limped home at 4300rpm and the oil pressure maintained 30-32psi. Landed and it was back up to high 40's. Has anybody seen this?

We are thinking the oil pressure regulator is the old style and plan to change that first, but any other thoughts?

Thanks in advance.

Click to expand...

Ideas - -

As Joe said, I'd first make sure the oil flow is not restricted from the tank to the pump. If the pressure does vary, then it would seem the sender is not the problem. I'd take the hoses off the cooler ( assuming no thermostat ), and blow thru the cooler and hoses. ( by mouth is fine ). Once drained, there should be very little restriction. Might even take the tank apart to see if anything was left inside that could be in the outlet tube of the tank. The hoses are 1/2" I.D. You should be able to blow thru them very easily.

Just for note - I did install the pressure relief kit, and have the original oil sender, relocated. I see 70# or more in flight.

This is odd . ..

I would take a diagnostic journey to gather hard facts. I assume you can statically replicate the condition on the ground so that a flight is not needed. Also assumed, is that the oil temperature is not way high, and the oil sump is not under/over filled.

1. Verify that the pressure change is real. i.e. eliminate failure of electrical connection or pressure sending unit.

2. If pressure is still low, then cut the filter to verify that there is no major failure of internal components that are causing an orbit of the crank to reduce the system restriction. Engines with inline or ver configurations can drop pressure at higher rpm when load is applied as it pushes the crank deeper in the bearing and clearance on the top side is opened up. Accompanying heavy knocking would be present. Opposed engines don't typically demonstrate this characteristic.

3. It might be possible that the driving of the pump is slipping. This would be rare and a design failure, but I have seen other failures where this happened.

I don't know this engine in detail, but a poppet style pressure relief will open at a higher pressure than it closes. Most engines have designed these out for that reason and the fact that they can hammer the seats under some conditions. The better design is a spool type valve, like a hydraulic spool. These are more durable and consistent over wide temperature ranges.

If it was/is suction issue like a leak or crack or restriction, it might cavitate at the pump inlet, but that typically just chops off the curve to a relatively fixed pressure.

Good luck, hopefully you will find a simple measurement issue. Gages and measurement systems usually fail before the actual engine parts.

YMMV

Are you downloading your data to Saavy Analysis?

I would, it's free, and then call one of the Rotax experts (Lockwood, etc) and give them access to your graphs....they should be able to narrow down the data to one or two possible causes.

It's an older engine, so first thing we're going to do is replace the pressure control spring and ball with the new style.

Second werewolf relocate the pressure sponsor to the firewall and add a second sensor for a simple pressure gauge as a cross-verify system.

Next we will look for restrictions in the feed line (maybe a kinked line?) or oil cooler.

Simple things first.

The mechanical gage is a good idea. I used a newly overhauled O-200 on my first homebuilt. I got no oil pressure in 30 seconds after the first start. I bought a cheap automotive oil pressure gage at AutoZone and tried again - no oil pressure. Hard as it was to believe the mechanic had not made a necessary mod when he removed the vacuum pump which resulted in oil pressure not being able to build up. The second gage verified the issue.