Wide range of oil pressure

[scsmith]

I have an IO-360-A1A (angle valve)
I use 15W-50 oil
I normally wait for take-off power until oil is at 125F. Fairly often, I will see oil pressure on take-off of around 95 PSI, occasionally a bit higher. Especially if I have just recently changed oil, it may even go up to 100 PSI momentarily.

At normal cruise, 2400 RPM, 180F oil temp, the oil pressure is 62 PSI. When it is a bit warmer out, and normal cruise gives 190F oil temp, the pressure will be 60 PSI.

The pressures are read on my Dynon EMS D-120, and I did verify the gage reading against a mechanical gage when first installed new (3.5 yrs ago)

So here's the dilemma, I can't lower the pressure regulator setting any lower, because I am at the minimum oil pressure for cruise. But my take-off oil pressure is above the "old" max pressure of 90 PSI listed in the 1970 revision of the Lycoming operators manual. I read in another post that later, Lycoming revised that value to 115 PSI. If that's true, I probably don't need to worry.

But I am concerned that perhaps there is a problem with the setting or function of any high-pressure oil relief component? Am I in danger of blowing the front crank seal out on take-off?

Thoughts?

[Kyle Boatright]

The pressure regulator acts like a pop off valve. It opens when the pressure exceeds some value. In your case, it is probably set to open at 95 PSI or so. Changing that setting won't impact your oil pressure during cruise. Take out one washer and see what happens. My guess is you'll see 5 psi less at takeoff and nothing else will change.

[DanH]

Swimming in the sump of opinion here, but I'd raise the pressure setting.

Same oil, same engine in this context. I want to see 75~80 psi in normal cruise below 190 and dipping into the upper 60's approaching max temp.

The high pressure alarm is set at 115 psi per the TCDS maximum. I wait for 100F absolute minimum post-runup, with (like you) 115F being more typical. The alarm will trip on the takeoff roll about twice a year, for just a few moments as viscosity is dropping rapidly with temperature rise. Remember, circulation is about 7 gallons per minute.

That said, is there any practical difference between what you have and my settings? Nope.

Don't worry about the front seal. It is subject to case pressure only, typical being less than 5" H2O.

[Walt]

Low oil pressure is usually caused by excessive bearing clearances (rods/mains). I'd be less worred about the high oil pressure at start than I would be about the lower than normal pressure at normal temps. If you can't maintain 75 psi at cruise, then you may have a more serious problem.

[DEWATSON]

What Dan Horton said......+ 1.

Also, engine oil pressure has nothing to do with crankcase pressure. Don't worry about you front seal.

[RonB]

Steve

I had the same problem a few months ago, called Dynon, ordered new oil pressure sending unit for the D120, installed and problem went away.

Quick and easy

RonB

[Ironflight]

Originally Posted by RonB

Steve

I had the same problem a few months ago, called Dynon, ordered new oil pressure sending unit for the D120, installed and problem went away.

Quick and easy

RonB

Hey Steve, RonB has a point here - I have replaced a couple of the can-type pressure 'ducers over the years on various airplanes because they tend to fail with a high bias when cold. Before I changed anything on the engine I would probably do another 'ducer cal to make sure there really is a problem.

Fundamental rule of MCC systems troubleshooting - when you see something funny, first ask how your instrumentation is lying to you....

[Pat Hatch]

Originally Posted by DanH

Swimming in the sump of opinion here, but I'd raise the pressure setting.

Same oil, same engine in this context. I want to see 75~80 psi in normal cruise below 190 and dipping into the upper 60's approaching max temp.

The high pressure alarm is set at 115 psi per the TCDS maximum. I wait for 100F absolute minimum post-runup, with (like you) 115F being more typical. The alarm will trip on the takeoff roll about twice a year, for just a few moments as viscosity is dropping rapidly with temperature rise. Remember, circulation is about 7 gallons per minute.

That said, is there any practical difference between what you have and my settings? Nope.

Don't worry about the front seal. It is subject to case pressure only, typical being less than 5" H2O.

Dan, my understanding is that raising the oil pressure is really just varying the setting of the pressure relief valve such that it will begin to relieve at a higher pressure. It should have no bearing on the pressure in cruise if it's below the pressure relief setting of around 95 psi. The output of the mechanically driven oil pump is fixed for a given RPM, and pressure would vary as a function of oil viscosity, temperature and downstream resistance, e.g., bearing clearance, and if pressure were to get up to 95 psi, it would begin to be bypassed by the relief valve. Just wanted to expand on your comment.

[rocketbob]

Personally I like 100-110 on takeoff when cold. At a constant RPM as is the case with an aircraft engine higher pressure correlates to higher flow, and if the oil cooler is large enough, better cooling. There is no danger of blowing the front seal off because its not pressurized with oil. A blockage in the crankcase vent will cause it to blow off.

[longranger]

Originally Posted by Ironflight

...Fundamental rule of MCC systems troubleshooting - when you see something funny, first ask how your instrumentation is lying to you....

"Stuff" runs downhill, and we instrumentation engineers seem to always be at the bottom to catch it... My pat answer when a test conductor questions a parameter, is "What do you want it to read?"

Seriously, Paul is absolutely right. Unless the sensor has been checked against a standard recently, you really don't know what the actual pressure is. And "new" doesn't necessarily mean "calibrated". Case in point: when my squeezer quit setting #4 rivets, the problem turned out to be that the gauge on my new pressure regulator was reading about 25% high.