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Oil pressure running high after engine is warm.

L

LN-BFD

Registered User
Higher oil pressure after the engine has warmed up isn't logical, is it? Well that is what happens. The oil pressure has always been on the high end of the scale on my plane. The other day I did a shallow descent to check out a potential landing strip. As I added power (only about 2100 rpm) to climb back out, I noticed the oil pressure almost hit the red line. I had a camera running. Check the indications here....its a bit grainy...edited from the corner of the picture youtu.be/5rAbOw3_ll8

Then I went through some of my older videos....and what do you know.... I have had this problem the whole time. Goes to show how well I scan my instruments. On this next video you can see the oil pressure nice and stable around 80 psi on takeoff with a cool engine. Then as the oil temp reaches 100+ or so, the pressure starts to increase and goes high again. youtu.be/Jl3BXsjVY6w I checked both the Oil Pressure Relief Valve, and the Oil Cooler Bypass Valve. The OPRV (non adjustable) spring had the right tension (read 8.92 lbs with a max allowable of 9.5 and min serv. 8.3)... so on the higher end. No washers in the housing. The ball was shiny with no wear marks. The OCBV on the other hand, had some scratches on the sidewall. Maybe from a grain of something. You could see it had made a pulsating pattern in different positions. Check the video here: youtu.be/ulJpzX3kYpM

This is what I think. The Oil Cooler has some sort of restriction. And I think it is more than just thick oil since I have been pre-heating both the engine oil as well as the oil cooler on cold days. The cooler is also covered during winter ops. And why does it happen like that? When the engine is cool the oil bypasses the oil cooler and flows easily. As the engine heats up, the vernatherm starts closing the bypass, forcing the oil through the cooler....where it meets higher resistance.

Any thoughts from anyone? The engine is an O320-A2B with the 160hp STC and the remote oil filter.
 
LN-BFD said:
Higher oil pressure after the engine has warmed up isn't logical, is it? Well that is what happens. The oil pressure has always been on the high end of the scale on my plane. The other day I did a shallow descent to check out a potential landing strip. As I added power (only about 2100 rpm) to climb back out, I noticed the oil pressure almost hit the red line. I had a camera running. Check the indications here....its a bit grainy...edited from the corner of the picture youtu.be/5rAbOw3_ll8

Then I went through some of my older videos....and what do you know.... I have had this problem the whole time. Goes to show how well I scan my instruments. On this next video you can see the oil pressure nice and stable around 80 psi on takeoff with a cool engine. Then as the oil temp reaches 100+ or so, the pressure starts to increase and goes high again. youtu.be/Jl3BXsjVY6w I checked both the Oil Pressure Relief Valve, and the Oil Cooler Bypass Valve. The OPRV (non adjustable) spring had the right tension (read 8.92 lbs with a max allowable of 9.5 and min serv. 8.3)... so on the higher end. No washers in the housing. The ball was shiny with no wear marks. The OCBV on the other hand, had some scratches on the sidewall. Maybe from a grain of something. You could see it had made a pulsating pattern in different positions. Check the video here: youtu.be/ulJpzX3kYpM

This is what I think. The Oil Cooler has some sort of restriction. And I think it is more than just thick oil since I have been pre-heating both the engine oil as well as the oil cooler on cold days. The cooler is also covered during winter ops. And why does it happen like that? When the engine is cool the oil bypasses the oil cooler and flows easily. As the engine heats up, the vernatherm starts closing the bypass, forcing the oil through the cooler....where it meets higher resistance.

Any thoughts from anyone? The engine is an O320-A2B with the 160hp STC and the remote oil filter.
Click to expand...

Calibrate your gauge before jumping to conclusions.
 
My plane does that. I just thought it was the multi-weight oil doing its thing (getting thicker) as it heated up. New oil cooler, so I don't think that's it.
 
If you have stock gage its thick (ie: 100w) oil in pressure line.clean line ,put thin oil in line engine to gage .
 
My engine produces its highest pressure when the oil is about 140-150 degrees, then begins a gradual decline as the temp increases from there. Although I do recommend checking the oil cooler circuit for restrictions, I don't think it's you're problem. The relief valve should keep the pressure in check. There are several different springs available and you may need a softer one. Multi-vis oil doesn't thicken with heat, it simply doesn't thin as much as straight weight. Filling the pressure line with thin oil won't change anything either. Regardless of the thicknesses of the oil in the line it cant cause the gauge to see an artificially high pressure. It will make the gauge respond more quickly to changes in pressure but that's it. Once you establish that the system is healthy I would shoot for a hot cruise pressure of 70 psi or so. Anything more is really just a waste of energy and adds heat. Opinion
 
I have gotten it backwards. If it is so, that the oil pumps the oil first through the oil cooler/OCRV then trough the pressure screen, then past the oil pressure relief valve before the pressure is measured.... Then the cold thick oil will have more resistance past all these items before the pressure is measured. Therefore a lower pressure indication with a cold engine. As oil heats up it passes more easily and now the oil pressure relief valve has to start doing its job. Since my spring tension is on the higher end of the scale, it explains the high pressure.

I need to do do two things: verify the pressure reading is correct and, if so, order a spring with less tension.

Tanks for all the input! I will post as soon as I have something new to report.
 
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I asked G and N engines about oil pressure and they said it could go as high as 100 I think I think the specs are higher than you think.
 
Preheat the line from engine to gage copper with hair drier and the gage,get them hot you will see the pressure come up right away,it's the thick oil in line and gage,this oil does not move,in twin with long lines we fill the lines with 5606.
 
Interesting

Thank you for the link. If it is so, I should maybe be just glad my pressure is where it is. Test run it today, and it's the same. Around 80psi until the engine oil reaches about 120F. Then it starts increasing. Maintains about 90-95 psi when RPM is between 2100-2400. I will leave it as it is for now.
 
this oil does not move
Click to expand...
Only has to move a minuscule amount. The oil is essentially incomprehensible, the pressure line is essentially non-expandable, and the bourdon tube has very little volume change to move and register a pressure change.

Besides, the question is why would the pressure go UP, not fail to register, though maybe you're saying it registers low initially, thus gives the impression of rising.

Agreed that thick oil in the pressure sensing line would act as a damper in the readout, especially if the thick stuff was at the damping orifice.
 
Last edited:
Guys a cold/frozen oil pressure line does not register any pressure! It would be 0 oil pressure.

I would take take a fitting and hook the two oil filter lines together bypassing the oil filter. Take that out of the system for troubleshooting purposes. Do you have a vernatherm on this engine?
 
Try putting a washer under relief valve housing. Should have copper one but add a washer as a spacer and see what happens. Too high oil pressure is rough on bearings.
 
don d said:
Try putting a washer under relief valve housing. Should have copper one but add a washer as a spacer and see what happens. Too high oil pressure is rough on bearings.
Click to expand...


Please read the thread on the biplane forum suggested in post #9 above. It would seem that Lycoming does not agree with you.

From above,

"...If you take this typical 10 psi drop and add it to the new 115 psi red line taken from the front of the engine, it is equivalent to a 125 psi red line at the old oil pump location"

That is how Lycoming is setting new engines.

Jack
 
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