Oil pressure fluctuates with RPM

[Helmetfire]

Why does my oil pressure indication fluctuate proportionally to engine RPM??

I always thought this was normal, but somebody mentioned that this should not be the case and the oil pressure should be consistent in terms of RPM and only decrease slightly as the oil temperature increases.

My oil pressure indicated around 55 psi on startup and would indicate around 65-70 psi at cruise rpm. Checked the pressure regulator and noticed it had 3 washers installed. We added another 3 washers and the pressure indicated about 10 psi more than before, but still varied proportionally to rpm. Either way, pressures would decrease slightly with higher oil temps which has always been the case. When we checked the regulator, the mech said the ball looked "worn", but hard to say if it was causing any problems, so we re-installed it with a few more washers to see what happened.

Hoping this has something to do with the pressure regulator, and not deeper in the engine as we just finished putting 4 new cylinders on. :-?

Any ideas?

Thanks

 

[PerryB]

That is absolutely normal. Oil flow through the bearings is relatively stable regardless of RPM. The oil pump output is variable and directly linked to engine speed. It's entirely logical that this would occur. Cars, trucks, tractors, boats and airplanes all experience this same effect.

Also if memory serves, that's a chrome plated steel ball on an aluminum seat. I seriously doubt the ball is worn. A 3 PSI rise with 3 washers added is just about right. I don't think there is anything obviously wrong with your oiling system. I think your mechanic is trying to fatten up the bill a bit. FWIW 75 PSI hot/cruise is plenty of oil pressure.

 

[mvivion]

What Perry said. I'd worry if you DID'NT see some fluctuation in oil pressure between idle and cruise.

MTV

 

[Coulee Clipper]

Can someone tell me why my oil pressure increases as the engine warms? Only when under power. Drops to normal when at idle. Slightly above midway at 100 goes to top of green at 170 or higher. rarely gets to 180 degrees.

 

[Coulee Clipper]

Lycoming 0-235. Lycoming couldn't tell me. Phillips XC oil.

 

[FrankO]

Just overhauled & installed an 0320 on my cub, oil press is proportionate to RPM (about 60 at idle, mid 70's at cruise). Completely normal.

 

[Helmetfire]

Thanks guys. I didn't think it was a big deal, but maybe he was having a senior moment. Super nice guy with loads of experience in the air and in the shop...don't think he'd intentionally steer anybody wrong. Theres always a good chance I misunderstood what he was trying to say...

 

[skywagon8a]

Can someone tell me why my oil pressure increases as the engine warms? Only when under power. Drops to normal when at idle. Slightly above midway at 100 goes to top of green at 170 or higher. rarely gets to 180 degrees.

Do you mean increase or decrease. Oil pressure is generally higher when cold reducing as it warms. In some cases it can be too high for high power settings until warmed enough to keep it below the max limit.

 

[Dave Calkins]

Do you mean increase or decrease. Oil pressure is generally higher when cold reducing as it warms. In some cases it can be too high for high power settings until warmed enough to keep it below the max limit.

Conversely, in some cases, when oil is cold in the line to the guage, sometimes The gauge does not indicate truly until the oil in the line warms up and allows the pressure to act on the gauge. Just sayin'

 

[180Marty]

Conversely, in some cases, when oil is cold in the line to the guage, sometimes The gauge does not indicate truly until the oil in the line warms up and allows the pressure to act on the gauge. Just sayin'

That's what my PA12 with O 320 does. Oil pressure increases about 15 lbs after you fly for awhile. Cessna 180 is opposite.

 

[PerryB]

Same here. When I first take off in the morning I'm around 70-72 PSI on the gauge after initial power reduction. When the oil temp is in the 140-150 range I see my highest indicated pressure, somewhere in the low 80's. As the oil continues to warm up, the pressure comes back down and typically settles around 75 PSI at 180 degrees. From there on out its pretty linear. For example 200 degrees will yield about 72 PSI etc.

 

[skywagon8a]

Conversely, in some cases, when oil is cold in the line to the guage, sometimes The gauge does not indicate truly until the oil in the line warms up and allows the pressure to act on the gauge. Just sayin'

I was thinking in particular of an Enstrom helicopter which I used to fly. The oil pressure would exceed the red line until the temperature came up and not necessarily on a very cold day.

 

[Dave Calkins]

I was thinking in particular of an Enstrom helicopter which I used to fly. The oil pressure would exceed the red line until the temperature came up and not necessarily on a very cold day.

R985's in the Beaver need gentle power application after startup, during warmup and preflight runup and first takeoff of the day due to high oil pressure like you said Pete.

My eyes go from the manifold pressure to the oil pressure several times on that first power up for takeoff.

 

[Coulee Clipper]

Oil pressure increases as the engine and oil warms. even after reducing RPM. I'm thinking that it's something at the gauge. I would expect some drop in psi at higher temps. Stays at the top of the green so I'll just keep an eye on it.

 

[skywagon8a]

Coulee, Do you have another direct reading oil pressure gauge which you can temporarily install? This will help you determine whether or not it is the gauge.

 

[Coulee Clipper]

Planning to do that at annual.