Oil pressure...how low is too low?
 

I have a '78 C20 with a rebuilt 350 and 700R4, I use Valvoline 10w30. At highway speeds it produces around 30 psi of pressure, and when it's at idle it produces around 5 psi. I have used 20w50 and it raised just a little bit, but not that much, I have installed an aftermarket mechanical guage to verify this.

Is this pressure acceptable? If not, what is the problem?

You should have 10 - 12 psi at idle with no less than 7 psi. Some of the things that can cause low oil pressure are a poor fit of the distributor, too large bearing clearence, oil pump of low quality reman, stuck pressure relief valve and loose or missing galley plugs. Good luck with it.

I wouldnt worry about it.. 5psi is a little low, but as long as its keeping the oil moving, you'll be fine. Its the pressure @ highway speeds thats really important.

pc

Your pressure is too low, you need to find the cause. How many miles does the motor have on it? did you consider using a stronger check valve spring ? at very least pull you oil pump and do a thorough inspection.

I disagree with every1 i think that 5 psi at idle is enough as long as the oil is moving because I have seen chevroelt motors run on that kind of oil pressure for a long time and if it dosent go below 5psi you should be find but below 5 I would try to fix i then

Too low is when the hydraulic lifters won't stay pumped up at idle, you can use the oil pressure gauge for a tach, and it take straight 50w oil to keep any oil pressure at speed. Aks me how I know.

What's wrong with you people? If you have 5 psi of oil at the REAR of the engine do you really think that you have enough pressure and flow at the FRONT. Can you say wipped out #1 main bearing.

man dont get me started on that, we have a satanic 454 out in the shop that doesn't like to hold oil presure. so far its killed, 2 cams, 1 crank and 1 set of crank and rod bearings. some blocks are made from the factory to hold and have high oil presure and some arnt its jsut the luck of the draw.

I think I have solved the prob. I went and bought a tach, turns out that my idle speed was like 400 rpm, cranked that up a little to 800 like the cam manufacturer recommends and everything is cool, now up to 15 lbs at hot idle in drive, jumps up past 20 in park.

Thnaks for all the info, I was kind of worried there :)

10# per 1,000 rpm, 15 -20# at idle. If less than that you have an unwanted,( usually to much clearance somewhere, or possibly porosity.), internal leak. You will be surprised at what an old big block or small block will run on. Want to scare yourself, put a -4 AN line on the front main plug, plumb it to a high quality oil pressure guage, go 30mph, then hit the brakes hard. You wouldn't believe how much that guage dances around if your short a little oil :D What I said about oil pressre is with the proper clearances in the bottom end. There are approx. 100 leaks in the bottom end of a chevrolet engine, rods, mains,lifters ect. These are by design. Look in an overhaul manual for proper clearances. If the engine runs good and doesn't rattle the lifters, drive it sometimes the stock guage or sender is screwed up.

:gmc:

Another answer; run it till it blows up, then put a little more oil pressure in the next one :devil: :D :D :crazy:

(that's a joke, I hope you people took it as one). :)

I've built numerous BBC & SBC street and drag race engines.

:gmc:

Unless one is going to throw a rod I run um till their dead. If its going to get rebuilt by me i'm not paying to machine all the old stuff, it will get a new rotating assembly anyway. I get about 10 on my 350 at idle with 10w-30, about 40 psi running down the highway.

I ran one fore a year that made 3psi hot idle. Never rattled a lifter. Was running fine. It was thrust bearings on that motor. I think the PO installed the harmonic with a hammer and that was the cause.

Main bearings are cheap. If it's a other wise good running engine with good compression then tossing some bearings it it will buy you a couple more years out of it.

maybe i'm use to the old deisels at work, but i don't wanna have oil press lower than 10 psi idle hot. thats just me. any lower than that, i feel i have a prob somewhere and will investigate why my oil press is that low. but agian, that is me.

man...now ya'll got me worried....my '78 350/sm465 idles with a psi of 0 at 350/400rpms....about about 30 at 2000rpms (main cruising rpm)....doesn't rattle at all tho....not that i've noticed.

0 psi is never good

i just figure the gauge is fubar....mine on my last truck was and it was newer then this one....the engine sounds healthy...no rattles or knocks or anything. gonna check this weekend with a mechanical gauge tho just to be sure.

I do agree with sanitysbane, in that zero psi is never good :)

if you have an old electronic guage, I wouldnt assume its all that accurate. Pull the valve cover(s) and make sure the rockers are getting oil at idle. If they are, drive it like you stole it. If not, then radio houston, because, we have a problem.

pc

thats about what i usually run with my tired 350. on the real hot days if its been running for longer than 30 mins then it will drop lower and starts idling like **** so i try to keep it moving and not idling once its completely warmed up

Mine does this too, and I cannot figure out why really. Once it's warm, it does not like to be stopped at a light. My truck runs the opposite from y'alls. Mine runs about 45 psi idle, according to the ghetto GM factory gauge. The 83 I drove for awhile did the same though, so Im not concerned.