Hi there everyone. I have a 1991 GTA with the mods listed in the sig. The thing is my oil press. goes all the way to 60 psi when the car is cold in the morning but after it has reached operating temp. the oil press won't go higher than 35psi even at 6000RPM. That's scary. Some have suggested I switch to a thicker oil because of the weather here. I'm currently using Mobil 1 Sync 10W30. The temp here is pretty much hot all the time (Puerto Rico). Could that really be the source of the problem. If it is,; what oil grade do you recommend? I thought about the oil cooler too but I don't think it would lower the press. so drastically. The engine was completely rebuilt about 2 months ago. Could be a defective oil pump, but then, it goes up to 60 psi in the morning. If I buy a new pump, would it be wise to get a high volume pump with the stock 5 quart oil pan?? A lot of questions but I need help please.

 

Have you made sure that reading is accurate by checking with a mechanical oil pressure guage? The stock guage is known to be pretty inaccurate.

Also, what is the oil pressure at idle?

 

When cold it idles at about 55psi and about 15-20 at op. temp.

 

That sounds normal. I would just check it with a mechanical guage to make sure of the pressure at all RPMs. You can get one for about $10 at any parts store.

 

What scares me is the 35 psi at 6000 RPM. Not sure why you're spinning it that high but that's another subject. The oil is either getting too hot and thinning out more tha it should, or you need to run a thicker oil to compensate for the weather. You could try a 10W40 or even a 20W50. I would get a gauge on it to see how hot it's getting. If it's getting too hot (230+) I would start looking for problems with the cooling system. That's what pulls the heat out of the motor (yes, the oil too). If it's inefficient b/c of the hot weather or as the result of poor maintenance, it will cause the oil temps to climb. If that all checks out time to look for oiling problems. If it's a higher mileage motor I would first look at oil drainback problems. If you've got sludge built up in the valve covers or lifter valley, you'll get poor oil circuilation.

 

rule of thumb-
10psi for every 1k rpm

 

Check the actual pressure with a mechanical guage first. The factory guage is notorious for being innacurate. Check the actual pressure first. You may not actually have any issues at all.

Also, wouldn't the '91 L98 have an oil cooler? Or was that just the Corvette?

 

It has a factory oil cooler but I disabled it in favor of a more efficient external oil cooler. The thing is my car runs at 170-185* There's no reason for the oil to get that thin. I contacted a tech guy from Mobil 1 and he told me that higher pressuer doesn't always mean better protection. He said the oil was flowing better through the engine and if the pressure is steady there should be no problem. I also read from a Melling engineer that if I'm using an oil cooler and remote oil filter I should use a high volume pump. I'm gonna install a high volume pump and pour in thicker oil, although 15W50 seems a little too much for me. I'm really not sure what to do.
BTW, the engine was rebuilt about 2 months ago.

 

What are the tolerances?

 

By whom? Was a new oil pump used? The clearance question is a good one.

I've never heard the part about using a high volume pump with an oil cooler. Have you routed it so the oil goes through the filter before it goes through the cooler?