Redsome

Hello everyone,

I'm here to seek for an advice about high oil pressure. The engine is 305 TPI with 74k miles on it ('91 5.0 V8 Trans Am)

I jsut removed oil pressure sensor and install mechanical oil pressure test gauge to see if sending unit is bad or if there's an actual pressure problem. The readings of the test gauge are 55 psi at idle and up to 60 psi when throttle is applied. Car has new oil (10w-40) and new oil filter and runs smoothly without any leaks.

So I need you guys who have experiences on 3rd gen engines to point me in the right direction. Is there any oil pressure relief valve that could be stuck besides the one in the oil pump? Oil pump is hard to remove since you need to lift engine up to take the pan off and that exceeds my DIY capabilities. Or is there any other week spots that could bild pressure up?

Any directions or suggestions are greatly appreciated.

Thanks.

IROCThe5.7L

Is this on cold engine? Sounds normal if so.

Redsome

Yes, this is on cold engine. But I have never had a pressure over 30 - 35 psi, no matter hot or cold engine, throttle or no throttle, needle was always steady and between 30 -35. So, when I noticed 55 on idle I shut engine off immediatly to prevent any damage that might be caused by high pressure. Is it safe to leave it running at idle for enough time to warm it up to see if the pressure falls?

IROCThe5.7L

That's completely normal. Your oil pressure is going to be higher on a cold engine. My stock L98 had around 50psi at cold idle. And around 20psi at hot idle. My new engine is 60 at cold idle. And 30 at hot idle.

Redsome

Well that's somehow a good news but I'm still bothered why my pressure on cold idling engine was around 30 in the past... Anyway, to conclude, 60 PSI at cold idle is not yet to be alarmed about? I'll just keep an eye on the pressure gauge more closely for the next few weeks and inspect oil look and level for any bubbling or leaking to see if things tend to go worse.

Thanks IROCThe5.7.

BHicks

Fresh oil also helps with the pressure. Once it warms up the pressure should come down some. I'd expect as it's driven and miles put on the oil and it breaks down some you will see psi return to what you normally see.
I use to have same thing with a 92 blazer. Granted it had like 200k miles. But always the oil psi would show like 10 lb at idle and of course increase under throttle. Every time it was close to time to change oil. Change oil and filter the psi go right back to 45-50 psi at idle until around time to change oil again.

Redsome

@BHicks. I changed the oil and filter becouse of sudden high pressure, not the other way around. I tought maybe oil gets clogged somewhere so I changed it and oil filter as well...
When I get home from work today, I'll let the car run for some time to warm it up to see if pressure will drop and then I'll report back.

Also maybe I should mention that before, car most of the time sits in the garage and when it is driven it's driven only for a few miles around the block becouse right now it's in the phase of thorough maintenance (body interior, exterior, light, brakes, paint, door panels, weatherstrips... etc.), so maybe all it needs is some long distance run...

Thanks.

whtltng89

Ive got a 91 350 with 320k miles and it always runs 50+ when cold but will run 40+ when hot at an idle and 50+ while driving

BASSETT IROC 85

iTrader: (2)

Might try a thinner oil. by 1991 GM was big in 5W30.

Redsome

OK, thanks everyone. Since a lot of you claim 55 should be normal on cold engine I'll just leave it there and only observe if it should go for worse... Like I said what got me worried was that I've never had such a high pressure in the past.

Thanks again.

bjpotter

Why are you using 10W 40? You have a low mileage car and should be using 5W 30. All 5.0L 3rd gen's of this year have a Mfg recommendation of 5W 30. I've always used it and my engines have run over 300,000 miles. It would also explain the rise in pressure if you switched.

Redsome

Actually according to Haynes for 3rd gens, recommended oil type depends on all year weather temperature differences. 10w30 and 10w40 are both recommended for temps from -14 to 38 degreess C (10 - 100 degrees F). But you're right, 10w30 is thinner so next time I'll probbably use this one.