oil pressure for 5.7L

[import.only]

okay guys, im new to this side of the forum. I finally broke down and bought a truck. well i have a '96 3500 with the 350. I've been told that these chevy trucks have alot of gage problems (fuel gage, oil pressure gage). Well this truck that I have has an oil pressure problem according to the gage. When the truck is cold oil pressure was just below 40. then as it wramed up pressure dropped low enough to where the "check gages" light came on at idle. I replaced the pressure sendor unit and now it reads even lower. I put a pressure gage on it the other day and the pressure is exactly what the sendor is telling me. Okay oil pressure problem right. But I was looking around for what the pressure needs to be at and in the maintenance manual for a 350 the pressure should be at about 9 psi at 1000rpm and 19psi at about 2000rpm. Is that right? what should the pressure really be?

[jveik]

thats wierd. my 4.3 vortec (a 350 with 2 cylinders hacked off the end) has about 40 at idle and 60 when anything other than that, when it's cold it runs at 75, or so says the guage. i read a book about souping up old school smallblocks, since im building a 383 stroker for my older truck, and it claimed that you need about 10 psi per 1000 rpm when youre racing at high rpms, so i would hazard to guess that perhaps you could get away with less at lower rpm's. basically the vortec-headed engines are old school rotating assemblies with newer heads and intake, although i think that they also are equipped with a roller cam instead of the old school flat tappet numbers

[MT-2500]

Originally Posted by import.only

okay guys, im new to this side of the forum. I finally broke down and bought a truck. well i have a '96 3500 with the 350. I've been told that these chevy trucks have alot of gage problems (fuel gage, oil pressure gage). Well this truck that I have has an oil pressure problem according to the gage. When the truck is cold oil pressure was just below 40. then as it wramed up pressure dropped low enough to where the "check gages" light came on at idle. I replaced the pressure sendor unit and now it reads even lower. I put a pressure gage on it the other day and the pressure is exactly what the sendor is telling me. Okay oil pressure problem right. But I was looking around for what the pressure needs to be at and in the maintenance manual for a 350 the pressure should be at about 9 psi at 1000rpm and 19psi at about 2000rpm. Is that right? what should the pressure really be?

I think what you are looking at there is the bare minimum specs.
But you need to get a manual test gauge on it the find the actual pressure.
A good sound engine will have 20-25 idle and 45-55 or more on the road.

[heavyredchevy]

My 89 K1500 with the 5.7L has 40 psi at idle and it pegs the gauge at higher rpm, cold. When It’s warm it has 30 psi at idle and around 40 at higher rpm. That’s with 5w30 oil.

[1968 Pontiac]

The oil pressure on my truck is similar to yours. The replacement engine, 350 I think even though the original was a 305, that was installed by the previous owner about ten years ago now has about 150,000km on it. He said that when he got the truck, the oil pressure was off the end of the dial, so he took it back to the shop where he said they changed/replaced some sort of spring; resulting in the low oil pressure. Any idea what spring may have been replaced? The previous owner said he's been running with the low oil pressure ever since the spring was changed with no trouble. On the highway the gauge is at about 200kpa when doing around 60mph, but when idling hot at a traffic light the gauge light comes on sometimes. The tires are LT265-75R16 with 3.42 gears.

[import.only]

Thanks for the input guys. I looked at that manual again and this time read the fine print, like "MT-2500" said, that is the bare minimum that the motor can run on. So I'm thinking bad oil pump, unless you guys have any other ideas. The oil has just be changed and like I said, the manual test gauge said my sendor is reading the right oil pressure. If it is the oil pump how much of a pain is it to get that changed out.

[MT-2500]

The oil pan has to come off.
On a 4W drive I have had to drop the front rear end to get the oil pan off.
Let us know how it goes.
Good Luck MT

[shakes77]

Just my problem but its worth a look. Watch the antifreeze level. My truck would start cold at 40psi at idle, then when it warmed up it would drop to around 10 psi at idle( this is with 5w30). Turned out I was leaking antifreeze into my engine. After going down to the head gaskets, truck now idles at 40psi cold and around 25-30psi idle after warmed up.

Nice jump in pressure I thought. This is a 1998 5.7L with 149,000 miles on it. Lower engine never rebuilt. Just lower intake manifold gaskets ( though I thought I would go down to head gaskets this time.)I always swore by the 10psi per 1000 rpm rule. A little higher is always better though.

[import.only]

Okay here is an update on my problem. I finally got around to changing the oil pump but the pressure is still too low. I think it might have dropped a little lower. I thought the oil had been changed recently, but when i drained it the oil was black and thick. I'm thinking that there is slug build up some where. Has anyone ever flushed the oil system? I heard of some stuff you put in and run it for a few minutes, then drain it and put your oil back in.
Is there a place in the oil system that can build up gunk? I've also heard that if the bearings are worn out, you could lose oil pressure. Does anyone have any other ideas?

As for dropping the oil pan, it really wasn't as bad as i thought it would be. I just had to drop the air guard where the flywheel is, and drop that part that the oil filter screws into. After that the pan came right out.

[MT-2500]

If you changed the ol pump and still have low oil pressure.
It wll be in worn out main or rod bearings or cam bearings.
Any one of the 3 or all 3.
Dirt or sludge build up helps oil pressure unless it is in the oil pump pickup screen.
You did check and clean that part right?
Flushing a old dirty engine will finish it off.
A little motor honey like old stp will help some and may get a few more miles out of it.
But it is Time to trade it off or rebuild or replace engine.
MT