Fluctuating oil pressure question

[avidflyer]

Hi all, lately, I've noticed my oil pressure doesn't hold steady at cruise rpm with my 80 HP 912 Rotax. It never goes real low or anything, but will go up or down as much as 15 lbs at the same rpm. I changed the oil pressure sensor yesterday, and had the same issue with the new electronic unit. Funny, but it will hold steady, and then shoot up and then come down back to where it was to start with. Ranges of pressure are from about 55 to 70 with the VDO unit, and 60 to 75 with the electronic sensor. I suppose I should run a mechanical gauge as a check, but both senders have shown the same thing, so I imagine the mechanical one will do the same thing. Any thoughts? Jim Chuk

[jiott]

A mechanical gauge is still worth doing. It will eliminate wiring problems, bad grounds, etc.

[jrevens]

Jim,

You also may possibly have a problem with the oil pump. Pressure is regulated with a spring & ball valve, which can use a shim to adjust pressure. I suppose there might be a possibility that things are not clean or maybe worn. Just a long shot.

[avidflyer]

It could be in the pressure relief valve, I did have that apart a week ago, came back from a flight with oil leaking out. It appeared to be coming out of the plug at the bottom of the pressure relief valve. Turned out to be leaking from the oil temperature sender just above it. The problem is though that I can't say if it was fluctuating before or not. It's kind of easy to miss if you aren't focusing on it. My gauge switches from temp to pressure then back again every second. Usually I don't watch it for any length of time, just a quick glance to see how things are. Pain in the neck to pull the pressure sensor off, I have to unbolt the cooler to get enough room to get a wrench in there. I have a mechanical gauge and the T I need, so I guess I better do it. Thanks for the replies. JImChuk

[avidflyer]

Well today I pulled the oil pressure relief valve out and washed it off in gasoline. Then reassembled it. Did a complete oil purge as well. Went for a 20 minute flight and the oil pressure held steady. Time will tell if there is anything else amiss, but so far it seems solved. Thanks for the replies. JImChuk

[Slyfox]

there is an updated relief for the pressure system on the pump. original is a ball, new is a mushroom and I think a new spring and screw in. I don't have the numbers but I'll look. it raised my pressure by 5 psi.

[avidflyer]

Thanks for the reply about the new style pressure relief valve. I was aware of it, and would have probably ordered it if this latest approach didn't work. About $50. I see the part numbers in front of me on a piece of paper from when I looked them up a couple days ago. For anyone else interested, I'll put them up. 8557 230 mushroom head, 838 122 is the spring. JImChuk

[Slyfox]

the bolt needs to be updated as well.

[avidflyer]

I hadn't read that. Interesting that they show the same spring and bottom plug, and either the ball bearing or mushroom head sits on top of the spring. Here is the link to leading edge catolog. JImChuk
912 & 914 Oil Pump Assembly, Oil Filter, Oil Temperature Sensor, Oil Pressure Sensor - Oil Systems - 912 & 914 Series Parts - 4-Stroke Parts 912 & 914 Series - Genuine ROTAX Parts - ROTAX Engines & Parts (leadingedgeairfoils.com) (https://www.leadingedgeairfoils.com/rotax-engines-parts/genuine-rotax-parts/4-stroke-parts-912-914-series/912-914-series-parts/oil-systems/912-914-oil-pump-assembly-oil-filter-oil-temperature-sensor-oil-pressure-sensor.html)

PS, after I posted this, I relooked at your post. I took your comment about replacing the bolt to mean the bottom plug. Maybe I misunderstood you?