Oil pressure question

[Chuck R.]

At cold start up and fast idle, oil pressure is between 65 and 70 psi.

While the engine slowly reaches operating temprature at idle, the oil pressure also slowly drops and holds at just above 20 psi.

When engine speed is increased to 1000 rpms or higher, the oil pressure responds instantly and holds between 45 and 50 psi.

I'm figuring even at 20 psi, the power plant is still getting completely lubricated, but I have never seen oil pressure on a small block that low at idle.

I have changed out the oil and filter but haven't fired the engine off yet to see if there is any difference.

Am I just being paranoid?

Chuck

[William C.]

Re: Oil pressure question

In '84, the idle on the crossfire TBI was so low that my then new '84 pulled about 10 psi when sittine at a traffic light in gear stopped. Found a bulletin about that time that idle oil pressure could get into the middle single digits without any problems as long as it comes up as soon as you go off idle. You should be fine.

[Joel F.]

Re: Oil pressure question

I don't think 20# at hot idle is a low number. Is it a stock pump or a hi volume or hi pressure?

[Chuck R.]

Re: Oil pressure question

That's good news.

Thanks for the mental sedative Bill

Chuck

[Chuck R.]

Re: Stock replacement Joel

After all this talk with high performance vs OEM pumps, I decided to play it safe and go stock.

[Pat M.]

Re: Oil pressure question

Hi Chuck. If you're talking about a C3 smallblock, my 70 has consistently had a warm idle in the mid-to-upper teens, and yet instantly increases like yours when I touch the accelerator. I think it's normal.

[Duke W.]

Re: Oil pressure question

Okay, lemme guess? The little icon thingy next to the thread says 1968/1969, so I'll go out on a limb and say it must be one of those two years, but my internet spys have been unable to tell me what engine option.

Duke

[Robert C.]

Re: Oil pressure question

Yes it would be nice to know what engine option you're talking about. Different engines, different oil pressure......

[Chuck S.]

Re: Oil pressure question

...Am I just being paranoid?

So, Chuckster, what up? ...Don't you believe that old gear head saying about "10 psi oil pressure for every 1000 rpm"?

That saying always seemed somewhat imprecise to me for idle conditions...at best it would have to mean absolute minimum allowable at idle, but...I think you're normal at 20 psi.

[Duke W.]

Re: Oil pressure question

The old 10 psi/1000 revs worked okay on production based Tran-Am racing engines 40 years ago, but was/is unnecessary on a road engine.

Current Sprint Cup engines are running 40 psi, 9500 revs, and use 0W-20 oil.

Do not try this on your vintage Corvette engine!

Duke

[Chuck R.]

Re: You know the ole NCRS saying Chuckster

Until Duke says it's ok, it's not ok

Well first off, I'm running a 3970010 350 block out of a rail road company line truck, so Duke please call off the spys ok? I don't want to inadvertantly shred one of your operatives with one of the claymores I have stategically located around the garage

Chuckster ole Pal, I always lived by the 10 per 1000 theory with Mopars and those "F" word cars, but because this is my first GM power plant rebuild, I'm just a tad nervous and needed mental hug I guess.

Thanks to all of you fine Gents for helping me get back into my comfort zone on this.

By the way, as I always do, I went out to give "Baby" her good night hug, I was shocked to find a puddle of coolant on the floor!

Pajamas be damned, I threw down a fresh piece of cardboard and started searching for the culprit.
What I found was a drip coming off of one of the motor mount bolts.

"Weird" I say to myself ( I talk to myself a lot lately) as I didn't think the threads for the motor mounts encroached into the water jackets. Well come to find out, this one didn't.

Upon further inspection, I found coolant seeping from around a lower head bolt, even though I had applyed teflon sealant to all of the bolts.

So after drawing off enough coolant to pull the bolt, I cleaned the bolt up and applied hi temp rtv, re-installed the problem child and re-torqued.

The drip is now no more. Neither are my jammies, I had to burn em, but I guess that's that's T.M.I. huh?

Chuckster

[Chuck S.]

Re: You know the ole NCRS saying Chuckster

Until Duke says it's ok, it's not ok

...Chuckster ole Pal, I always lived by the 10 per 1000 theory with Mopars and those "F" word cars, but because this is my first GM power plant rebuild, I'm just a tad nervous and needed mental hug I guess...

Well, if you ever buy a later GM product with an LS series engine, don't apply what you just learned about yer ole SBC...idle oil pressure on a new LS series engine is 30 psi!!!. Different time...different engine.

[Duke W.]

Re: Oil pressure question

Over the years since the first "energy crisis" mfgs have applied many design changes to reduce internal engine friction. One that began back in the seventies was reducing oil pump flow volume. This means lower idle oil pressure and maybe less peak pressure.

The bearing load at idle is very low and load increases with the square of speed, so little oil pressue is required at idle - typically no more that 5-10 psi will provide plenty of oil flow at idle speed, and the lower the idle speed the less the pressure. If an engine has loose bearing clearances low idle pressure is typical, and it may take more revs to build up to relief spring pressure

So if a typical engine has at least 5 psi at idle and it increases rapidly above idle and achieves at least 25-30 maximum it will not suffer in typical road use.

My Cosworth Vega typically runs 70 psi warm above 2000. When I reindexed the cams to remove much of the overlap I was able to drop the idle speed from 1200 to 900 and hot idle oil pressure dropped from 40 to 20 psi - no problem. Pressure above about 2000 remains the same.

The 10 psi/1000 revs was a recommendation 40 years ago for SBs that were modified for racing, and racing engines are a completely different animal than mild road engines.

Duke

[Chuck R.]

Re: Good Info.

Chuck, the only way that I'd be dealing with a later vintage LS engine is if I run into one at an intersection my friend

I had friend who ran a Cosworth Vega. He made a lot of money on weekend nights!

I'll tell you what, light to light and pound for pound they were down right quick and could they turn up some RPMs

When he finally got rid of it, it was burning a quart of oil to every 100 miles oil and had a serious low end knock. Even then it would still haul the mail.

His was white and gold I'll bet yours is/was black and gold Duke

Chuck

[Duke W.]

Re: Oil pressure question

It must have been boosted. There's only so much you can do with a 2L naturally aspirated engine in a 2700 pound car no matter how good the head and still maintain reasonable road manners. In F2 trim it can make about 290 gross at 9000, but this configuration actually has less power than a "massaged" OE engine up to about 4500, and it will barely idle at 2000, which would not be a very pleasant setup around town.

Mine makes 122 @7000 SAE corrected HP at the rear wheels - about 145 net at the flywheel on a 8.2 CR and unleaded regular. It was rated at 110@5600 SAE net HP at the flywheel, and in its current state it's about as fast in a straight line as a modern 2L sedan of similar weight.

Where the car excels is braking, handling, and overall balance (after a few mods with some off-the-shelf GM parts from the H-special), and it embarrassed a lot of name brand sports cars at Riverside and Willow Springs track events for about 15 years.

Duke