Weird Oil Pressure Fluxuation

[Delta Whisky]

So, I have this observation - wondering if others have seen it and what might be the cause. Sometimes on or just after take off, my oil pressure drops. Often to the point that it triggers the conservative oil pressure warning light and that gets my attention. Maybe the trend happens all of the time but the oil pressure doesn't get low enough to trigger the warning - I just don't know.

Here's what it looks like:

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Although the graph is barely readable it shows the drop and recovery and then things are relatively stable for the rest of the flight.

Any ideas or is this normal? In my wildest imagination I can't think of what would cause this in a dry sump engine.

[Shadowrider]

Interesting? Whats the relationship to oil temp? Can you post a better picture? Does is always do this? What about after you have been flying and then land and take back off?

[avidflyer]

What are you using for the gauge and sender. Recently on my 912 UL, it started showing 120 or more at low rpm. I changed the VDO sender and now it's all back to normal again. Can you install a temporary mechanical oil pressure gauge to compare? JImChuk

[Delta Whisky]

Dustin -Oil temp showed a steady rise from 133F to 146F during the time the oil pressure was outside of norm - 56 seconds below 40 lb/in2 in this case. (40 is the lower 3 sigma limit) It has happened on first flight of the day (this event was one such) and indiscriminately during landing practice on other days. (Not that I need the practice of course.)

A more readable chart should be attached.

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Jim - I didn't consider a gauge issue due to the fact that when this happens it is always at the same point in the flight profile - just a few seconds after take off. I remember my warning limit low to be 35 lb/in2 and in this case the first time at trigger or lower was about 35 seconds after starting the take off roll and the last event was 21 seconds later.

Thanks for your interest and comments.

[Shadowrider]

I think I am with Jim…making sure it’s not an indication or sending unit before starting to chase oil pressure issue.

[atosrider]

how old and tired is the spring in the oil pump, you can disassemble and check for wear marks ...

my 912UL will have lower pressure on higher revs during warmup

I'm not too happy seeing the reading slowing fluctuate 5psi during flight, and this is with new spring and ball in the pressure relief gallery

[GuppyWN]

I had fluctuations in my oil pressure. I ordered a new spring and mushroom piston to replace the ball. That was a few years ago. Works great.

[Delta Whisky]

Thanks gents - all good issues to check out and I will as soon as the manifold balance tube mod I started is complete.