24 replies to this topic

[HUNTER ZR2]

In the last 20k miles I've owned the truck I have watched the oil pressure slowly decline. When I first got it stayed at 40. After that it stayed just a hair below 40 and now it's anywhere from 20-38ish depedning on RPMS. What is normal pressure? Motor has 169k miles on it as far as I know.

[ducksface]

1 pound per 100rpm is acceptable. Others will disagree. My vette runs 5 or 6 pounds at idle and 40 at 4000. Many of my cars have.
Old school trick is to run thicker oil. Others will disagree.

[HUNTER ZR2]

I've been using 5w-30 Castrol GTX high mileage and ac delco or wix filters.

[HUNTER ZR2]

bump

[raven2510]

Well my truck is the same way. 1999.
I'm at about 25-40 idle warm, but it increases with rpm. I have put 60k on it with no issues.
I wouldn't worry about it. From what I have read, its a common thing with all chevy engines.

[Benielsahn]

Have you switched oils? If the engine was run primarily with conventional oil, sludge and deposits may have been collecting in orifices and passage ways the oil travels through. More restriction would cause slightly higher oil pressure. The generally accepted theory is that synthetic oils break down deposits and therefore reduce restrictions. Kind of like plaque in your arteries.

[jwwaldschmidt]

Remember, pressure = resistance to flow. Higher pressure is not always a good thing, as Ben alluded to above.

If you're running OEM spec oil, I wouldn't worry about it too much. Pressure should go down slowly with more miles, as tolerances are slowly worn out. As long as you have some oil pressure, you should be fine.

[HUNTER ZR2]

Truck was wrecked, I have no way of knowing if the previous owner used synthetic oil or not. I've started using that highmileage GTX and it says synthetic blend in small print. From what y'all are saying I get the idea this is normal, thanks.

[killian96ss]

The minimum oil pressure needed on most Chevy V6 and V8 engines is 10 psi per 1000 rpm. You can get by with a little less, however the risk of engine damage does go up, especially when the engine is under load. Switching from the recommended 5W/30 oil to a 10W/30 on higher mileage engines will safely increase the oil pressure. A synthetic oil of the same weight as a standard oil is much thinner! You can even see the difference when your pouring each one. In other words a synthetic 10W/30 has about the same consistency as a regular 5W/30. Synthetics are expensive, however you can run them 2 to 3 times longer than standard oil. This puts the cost about the same and synthetics plus are proven to reduce wear much better than reg oil so it only makes sense ( at least to me) which one to use.

Steve

[jwwaldschmidt]

10psi per 1000 rpm -

I haven't seen a single truck that would 55PSI of oil pressure at redline. That doesn't seem right to me, at all.

I've seen SBC's idle at 5PSI all day and never have issues.

[killian96ss]

I have 3 Chevy's outside right now (88 S10, 96 Impala, 05 ZR2) that never have less than 30 psi at idle even when the outside temps are over 100 degrees and usually run about 40-50 psi during normal around the town driving. All 3 have factory oil pumps, nothing high volume or high pressure, and are running 10W/30 synthetic Mobil One oil. 10 psi per 1000 rpm has been the minimum oil pressure recommendation for Chevy engines longer than I've been alive, lol. In fact every GM shop manual I have states 10 psi per 1000 rpm! There is something wrong with any engine that only puts out 5 psi at idle! If bearing clearances are not set right even a brand new engine can have low oil pressure. The 10 psi per 1000 rpm rule is not scalable which means even though you should have at least 10 psi at idle, you don't necessarily need 50 psi at 5000 rpm.

Steve

[ducksface]

What there is;
Is something wrong with mathmatical ability.
10 per thousand is 1 per 100.
550 idle would 5.5lbs.

The question was minimums.

[killian96ss]

Yes, technically you are right, but keep in mind this is the minimum oil pressure needed to prevent accelerated wear and engine damage. You should not be running at the minimum! Double the minimum and you are now back in the low end of the normal range. 10 psi at a 550 rpm idle is the lowest I would accept, but that's just me.

Steve

[N2O_ZR2]

I haven't seen a single truck that would 55PSI of oil pressure at redline. That doesn't seem right to me, at all.

Really? I don't remember exact numbers, but I think I'm close to that.

[ducksface]

Vette does 5 at idle (I worry a bit)
Does 60 at 4500rpm

[HUNTER ZR2]

Needle doesn't fall all the way back down when truck is off either, have to turn key back on to first position and then off again to get it to the rest position. I guess I might try 10w-30 GTX high mileage next time, anything wrong with that?

[Wags]

I had a high oil pressure problem in my 2000 S-10 when my t-stat was stuck open. The oil pressure would not go below 40psi ever. The engine was circulating all of the coolant all of the time (in the winter) not allowing the truck to warm up properly. This caused the truck to run in open loop mode (computer thought engine was not warmed up) all the time. This caused the oil pump and pressure to be at no less than 40psi and up to 80 on acceleration all the time. Once I replaced my t-stat all was good oil pressure was at 20psi after warm up @ idle. So If you have a lower temp t-stat or stuck open t-stat that may be a reason or cause of your high oil pressure...just sharing from my experience.

[Dizzi]

Hey guys im new to this forum my 97 z has 259,500 miles on it and has 40 psi at start up I bought it for 1500 bucks the previous owner gave me the service records of oil changes every 3000 miles. Many mods to come here is a good pic of my old 84

Attached Files

•  Image0056.jpg   185.24K   14 downloads

[killian96ss]

I had a high oil pressure problem in my 2000 S-10 when my t-stat was stuck open. The oil pressure would not go below 40psi ever. The engine was circulating all of the coolant all of the time (in the winter) not allowing the truck to warm up properly. This caused the truck to run in open loop mode (computer thought engine was not warmed up) all the time. This caused the oil pump and pressure to be at no less than 40psi and up to 80 on acceleration all the time. Once I replaced my t-stat all was good oil pressure was at 20psi after warm up @ idle. So If you have a lower temp t-stat or stuck open t-stat that may be a reason or cause of your high oil pressure...just sharing from my experience.

The PCM has no control over oil pressure. The oil pump is directly driven by the cam and is not variable. A t-stat that is stuck open or closed or one that is too cold does not have any effect on oil pressure. Temperature is the only thing that can affect oil pressure. The hotter the oil, the lower the pressure, and vise versa.

Steve

[spt]

10psi per 1000 rpm -

I haven't seen a single truck that would 55PSI of oil pressure at redline. That doesn't seem right to me, at all.

I've seen SBC's idle at 5PSI all day and never have issues.

I'm at 188k miles, running Mobil 1 10w30: Idle oil pressure is 40 cold, 30ish hot, and at 2200 rpm it's at 60 psi...

It was about the same with the 5w30...