Oil pressure off the scale on cold start

[pawn_that_dude]

On m 84' GL 4WD (EA81) I've had some high oil pressure problems on cold starts first thing in the morning:

1. Starting up, oil pressure sits at 50-60psi, which is totally normal for me.
2. I rev it past ~2-2.5k, the oil pressure will slowly rise then shoot up past the top of the scale and stay there.
3. I turn it off, the oil pressure falls after 10-20 seconds, sometimes with a faint audible click, and shoots back down.
4. If I let it idle at ~1k until the temp hits the bottom of the gauge, the oil pressure won't rise, and the oil pressure will be totally fine for the rest of the drive. It never goes above 60psi even revving it hard.

Here's a video: 

 

Edited September 27, 2018 by pawn_that_dude

[Dee2]

Probably your oil pressure sensor or your gauge is malfunctioning.  Try replacing your sensor and see if that makes a difference.  

[nipper]

I vote sensor

[GeneralDisorder]

It is normal to peg the gauge when the oil is cold. 90+ psi is easily possible with cold oil. Subaru engines have the unfortunate consequences of being aluminum block / iron crank. This means when cold the clearances are twice as small and that only makes the thick oil situation worse. Oil pressure is the consequence of resistance to flow. Cold oil naturally resists flow, and so do tight clearances. 

Don't load the engine when cold. The rod bearings and heads will not receive an adequate oil flow for loaded conditions. Aluminum block engines must always be brought up to operating temp prior to loading. 

GD

[Subasaurus]

12 hours ago, GeneralDisorder said:

It is normal to peg the gauge when the oil is cold. 90+ psi is easily possible with cold oil. Subaru engines have the unfortunate consequences of being aluminum block / iron crank. This means when cold the clearances are twice as small and that only makes the thick oil situation worse. Oil pressure is the consequence of resistance to flow. Cold oil naturally resists flow, and so do tight clearances. 

Don't load the engine when cold. The rod bearings and heads will not receive an adequate oil flow for loaded conditions. Aluminum block engines must always be brought up to operating temp prior to loading. 

GD

quick question GD, are Subaru Cranks Cast or Forged? i've been wondering that for a while, im sure the new ones are Cast, but were any ever Forged?

[GeneralDisorder]

All Subaru cranks are Forged. The design having too many main/rod bearings too close to each other precludes the use of a casting. It wouldn't hold up. They are very thin in cross-section between the bearings. We routinely run the stock nitrided EJ257 crank up to 600+ HP with no problems. 

[Subasaurus]

On 9/28/2018 at 1:27 PM, GeneralDisorder said:

All Subaru cranks are Forged. The design having too many main/rod bearings too close to each other precludes the use of a casting. It wouldn't hold up. They are very thin in cross-section between the bearings. We routinely run the stock nitrided EJ257 crank up to 600+ HP with no problems. 

Appreciate it! that just made me love my Subaru's even more

[pawn_that_dude]

So somehow I never saw the replies on this thread I created! Wish I would have. This "problem" was so annoying in cold weather. What doesn't make sense to me is how the oil pressure can still be pegged long after the car has warmed up. But if I turn it off and back on to reset the pressure after it's good and warm, I can rev the nuts off it and the pressure won't spike. It seems very binary to me.

I did replace my oil pressure sensor. The old one was leaking, so might as well. I finally found one that would work for my '84 GL 4WD wagon: Beck Arnley P/N 201-1341. Behavior is exactly the same, however. Which is at least encouraging that the pressure reads the same between two different sensors.

In the meantime I also added an oil pan heater pad. Anyway, seems like a ton of people who live in somewhat cold places have this problem, so I just won't worry about it. Seems to happen for me if the temperature overnight is below 50 (it doesn't happen in the summer).

Edited February 28, 2019 by pawn_that_dude