High Oil Pressure

[1987 Porsche]

I have an 86 Turbo and did a whole engine tune up and changed every seal and gasket on the car. Oil cooler re-seal was also done and I am noticing that on initial startup I am pegged at 5 bar. Once car warms up the lowest it goes to is 4 bar. When I did the reseal I used the alignment tool. I do have the older style, 3 piece OPRV. I did change out the oil sender with a new one and that still did not fix the high pressure indication. Also the wires to the sender are connected to the correct terminals. Do you think for some reason the OPRV is binding, even though I used the alignment tool? I cant seem to figure out why its indicating high. Any suggestions would be appreciated.

Lou

[Eskozki]

What kind of pressures did you see before you did the reseal? How hot is warmed up? My NA is up at 5 bar when starting, after driving for a while the idle pressure is around 4 bar and after longer period of driving I'm seeing 3 - 3,5 bar pressure at idle.

[walfreyydo]

Double check the OPRV isn't binding. Alignment is critical when installing the oil cooler housing and there is a tool which will set the alignment of the housing when you install it to ensure that the OPRV goes in and has perfect alignment to open and close.

Also if the wires on the sender are reversed this can also show high oil pressure. Try swapping the wires just to see if that solves the issue before looking at the OPRV.

I have heard that oil will spray past the oil filter gasket if oil pressure is pegged high from a binding OPRV.

Lastly, it is normal to see up to 5 bar oil pressure on a cold start at idle, but should drop down to 3-3.5 once fully warm.

[wildcat077]

You don't want your oil pressure to peg due to a faulty OPRV , i had two oil fires on my race car due to the oil pressure blowing out the seal of the oil filter and oil onto the header.
I went out and bought a brand new later unit from the dealer, keep in mind your three piece OPRV is 30+ years old ...

[wildcat077]

You don't want this ... my fire suppression system saved my car from burning to the ground , but on a street car that's no bueno !

[1987 Porsche]

Guys thanks for the replies. I bought the car last year and only drove it a few miles prior to disassembling a good part of the engine in order to stop leaks. So in regards to a baseline oil pressure I do not have one. It seems from what I am reading 5 psi at start up and 3 to 3.5 when warm is normal.

Eskozki- Once your car is warm and you see 3 to 3.5 at idle, how high does it rise when driving at normal speeds. Does it peg out at 5?

Phil what's a normal pressure when warm on your car?

[kdjones2000]

Your car is normal. Pegged at cold, drops down when it warms up.

[Eskozki]

[QUOTE=1987 Porsche;11975964
Eskozki- Once your car is warm and you see 3 to 3.5 at idle, how high does it rise when driving at normal speeds. Does it peg out at 5?

Phil what's a normal pressure when warm on your car?[/QUOTE]

While cruising at 2-3k rpm the pressure reads around 4 bar.

[wildcat077]

I woulnd't be able to confirm my oil pressure in bars because i have an Autometer gauge in psi's in the race car, but it's above 60psi at 3000 rpm and above and hovers around 40 psi at idle !

[1987 Porsche]

I just took it out today and drove it around for about a half hour. When I finished the drive, sitting at idle pressure is at 3.5 bar. When driving around and the car is warm at 30 mph and two thousand rpm in fourth gear its pegged out at 5. At 50 mph at 2500 rpm in fourth gear it is once again pegged out at 5 bar.

[1987 Porsche]

Here are some pictures.

[1987 Porsche]

[walfreyydo]

Originally Posted by 1987 Porsche

I just took it out today and drove it around for about a half hour. When I finished the drive, sitting at idle pressure is at 3.5 bar. When driving around and the car is warm at 30 mph and two thousand rpm in fourth gear its pegged out at 5. At 50 mph at 2500 rpm in fourth gear it is once again pegged out at 5 bar.

This is normal! See Clarks

Originally Posted by walfreyydo

Lastly, it is normal to see up to 5 bar oil pressure on a cold start at idle, but should drop down to 3-3.5 once fully warm.

At RPM's higher than idle, especially if the oil isnt fully warm, its normal for the oil pressure to be up near 5 bar. It also somewhat depends on the oil viscosity you are running.

[1987 Porsche]

I am running castrol 20w50.

[Monkey Wrench]

Originally Posted by 1987 Porsche

It seems from what I am reading 5 psi at start up and 3 to 3.5 when warm is normal.

1 bar of pressure is 14.5 PSI , that's near to what atmospheric (air pressure at sea level at standard temperature is 14.696 PSI )
2 bar is double that. or 29 PSI and so on.

the two measurements are directly proportional so you can just multiply by 14.504 to get PSI or divide by the same to get the pressure in bar. It will never change. Physics is like that, there are very few breakthroughs or advancements or changes in general physics.

Don't worry if your gauge is not in bar or PSI, you can simply convert. the only difference is the numbers on the face of the gauge. Don't replace the gauge or be confused. You can use google or any converter to do it without any math. You can ask your phone if you like to do that.

5 Bar equals 70.4 PSI
3 Bar is 43.51 PSI
3.5 Bar is 50.76 PSI

most gauges will ignore atmospheric pressure or read 0 at rest but this isn't necessarily always the case. If it's an accurate scientific measurement then the current atmospheric measurement, temperature etc might be important. For this you can ignore that,

Someone like a racer might be in tune with adjustments for altitude, barometric pressure etc. if the air is more dense you get more in and that will vary with temperature, elevation etc. High altitude means thinner air. It changes with the weather. hot air is "thinner" than cold air.

[wildcat077]

Not sure , but 5 bar at 2000 rpm when the car is warm seems a little high ... looking at Monkey Wrench's graph you would be at 70+ PSI ?
Best thing you can do is try to borrow a proper one piece OPRV , align it correctly and see if the oil pressure changes , at least it would narrow it down to the gauge or the OPRV.

Cheers
Phil

[Monkey Wrench]

70 seemed high to me but maybe others have more experience.
with low pressure you might not get the oil distribution you need. I'm not sure what the reprecussions of high oil pressure are. blowing the oil cooler parts maybe?

I think a lot depends upon the spring pressure on the ball which limits max pressure. if the spring were too tight it would increase pressure but only when the set limit is exceeded.

if clearances were loose in crank and rods or a worn oil pump then it might have low pressure in which case the ball (pressure relief valve) isn't in play.

won't hurt to pull the plugs and turn the crank by hand just to see if anything feels tighter than it should be. It won't tell you much unless the crank is hard to turn with the plugs out in which case it might mean something is binding.

maybe those more experienced can reflect if they think 70PSI is too much. there is likely an official spec.

pressure isn't created by the pump. You need resistance to flow and a pump to have pressure. a lot of machines have a hydraulic pack and they always have a pressure relief valve to set the maximum pressure. Its normal for a system like that to always be running the pump and simply bypassing fluid back to the tank so that the pressure is there when needed. the tanks get quite warm just sitting there with the hydraulic pressure ready when needed to move a cylinder etc. They do require considerable energy even when the hydraulics are not used. often the tanks are big to allow more oil for cooling capacity.

in a car I dont know how much time that pressure relief valve would spend open, maybe it usually is but it can't open until it meets the set pressure which relates to the spring tension. if the system is running too high in pressure maybe that tension can be adjusted to bring it into spec. its main purpose is to limit that high set point in pressure. the pump needs to always run otherwise it would break the pump or other related parts.

If you are idling and it is 20 PSI or similar, it is not near the setpoint and adjusting it wont change anything. That pressure relief ball is closed unless it overcomes spring pressure with high enough oil pressure. once the spring tension is overcome the ball lifts and oil passes back to tank to prevent over pressurization.

I dont have all the answers but the pump is a gear pump which means it has a set displacement for a given RPM, the pump can develop wear and slippage which may slightly reduce the GPM rate. perhaps there is more flow when bearing clearances become larger. maybe racers know more about that stuff. could it be that some larger clearances in main and rod bearings results in higher oil flow and better cooling ? maybe?