High oil pressure mystery

[jrs14855]

The oil pressure reading at the front of the RH gallery will be approximately 10# less than at the location near the right upper engine mount. Cessna has been using the front location since the restart of single engine production.
so if your oil pressure in a late model 172 reads 80 psi it is really 90 psi. The higher oil pressure is helpful for valve lubrication.
The oil pressure maximum red line has been 115# for start and warm up for many years.

[Paul Eastham]

Originally Posted by lr172

If you also have 100 PSI at that sender, you likely have some type of blockage.

Are you sure about that? If the pump/regulator is leaving the pressure too high, won't that carry through to the post-regulator pressure?

[Bud K]

Paul, interesting post. Did you ever solve your high oil pressure problem? My TMX-360 oil pressure is also running high, sometimes. I too have a Dynon D10 EMS. During level cruise, 2500 rpm, my oil pressure changes from a normal 82 psi then climbs to around 105 psi. After a few minutes, the pressure returns to 82 psi, then back up to 100+. Changing engine rpm (down to 25% power) does not affect the high pressure indication. I have a VDO pressure transducer remote mounted on the firewall fed by a hose from the 'normal' oil pressure sender location (per my A&P). I have a new pressure transducer on order and I haven't tried removing and inspecting the pressure regulator yet.

[edsong]

I just went through this problem in my 8. My Skyview also warned me at 100 psi. It usually runs 90 on takeoff and 75 once its at operating temp(185ish). I saw 105psi and that got my attention. I have a Skydynamics 4 into one exhaust that vents the crankcase gasses in the center of the collector. Carbon deposits built up in the pipe until it was about 80 percent clogged.
Cleaned it out with a metal brush (that looked like a pipe cleaner) and a drill.
330 hours on the engine. I think i'll clean it out at every annual now.

[lr172]

Originally Posted by Bud K

Paul, interesting post. Did you ever solve your high oil pressure problem? My TMX-360 oil pressure is also running high, sometimes. I too have a Dynon D10 EMS. During level cruise, 2500 rpm, my oil pressure changes from a normal 82 psi then climbs to around 105 psi. After a few minutes, the pressure returns to 82 psi, then back up to 100+. Changing engine rpm (down to 25% power) does not affect the high pressure indication. I have a VDO pressure transducer remote mounted on the firewall fed by a hose from the 'normal' oil pressure sender location (per my A&P). I have a new pressure transducer on order and I haven't tried removing and inspecting the pressure regulator yet.

Those symptoms point to a failing sensor and I would replace that as a first step. Those VDO sensors are not known for long-term robustness.

Larry

[edsong]

That's what I thought too Larry. I'd still check the breather. If it gets plugged it could push the prop seal out and then you'll have a real emergency.

[Bud K]

Originally Posted by lr172

Those VDO sensors are not known for long-term robustness.

Larry

Interesting comment about VDO sensors. I have also been having an occasional problem with my Fuel Pressure reading high. When it reads high, it doesn't matter if the boost pump is on or not. I thought that it was a bad sensor ground but the sensor is mounted to a manifold bolted to the firewall. It too is a VDO sensor. That might be my next sensor replacement.

[lr172]

Originally Posted by edsong

That's what I thought too Larry. I'd still check the breather. If it gets plugged it could push the prop seal out and then you'll have a real emergency.

In order to increase your oil pressure by 20 psi, your crankcase pressure would have to be either 20 PSI or 100 PSI, not sure which. Either way, it seems HIGHLY unlikely that your front oil seal could handle that much pressure. You would also see problems with fuel pressure/delivery with this type of crankcase pressure.

Larry

[Bud K]

Well, my mystery has been solved. It was indeed the VDO oil pressure sender unit. It was a simply fix.