I have a 1990 305 TBI. Only the stock gauges. What should the oil pressure read? It starts out ~38 when cold. After it is warm it is any where between ~28 and 33 when driving. I understand that this gauge is not the most accurate and that the pressure should vary as I drive etc. I just do not know what the ideal value is for this car.

 

That sounds about right. Under small load , like idle, my oil psi is about 30-35psi. When I floor it (WOT) it jumps to 45-50 psi

 

In an ideal world 10 psi for every 1000 rpm you spin on a small block Chevy.
Factory gauges are notoriously inaccurate so if you are worried about it put a mechanical gauge on it.

If my car only had 30 psi at 5500 rpm i would be babying it until I had another short block to install.

 

Thanks for the reply. I just put it on the road on Monday and am still checking it out. I have not driven it hard at all. Only 'floored' it once or twice, smiling not watching gauges. the 28 - 30 is highway when it is not turning many RPMs. Beginning of the day it is higher but drops after a few miles after it warms up.

 

I did an oil change and got 60+ psi at idle.
It went down from there as my engine consumed the oil and created a smoke screen so no one could see what I was up to.

My engine has lots of problems.

Question: If my dipstick was not seated correctly, I would add more oil to compensate for the increased height of the stick, right?
This increase in oil volume would increase the pressure too?

 

That's a bit low-ish compared to "normal", but plenty acceptable.

The "10 psi per 1000" is an old racer's rule of thumb for SURVIVAL, and good enough for answering the question "is it ENOUGH" in a RACING situation. It is not appropriate to a street motor, and in no manner way shape or form describes "normal" behavior of ANY engine EVER built. Ignore it for the purpose at hand.

You very well might. However, "not seated correctly", assuming that doesn't mean "was laying on the ground", wouldn't result in an error of more than half a quart or so, unless ... well, let's not go there.

No.

The pump draws in oil and pressurizes it. It is a "constant volume" design: it always draws in the same amount per rev, and the pressure is determined by how fast it bleeds down through all the engine's clearances. If it exceeds some preset amount, a bypass valve opens, thus limiting the max that it can ever be. The amount laying in the sump has no influence, directly, on the pressure.

 

NO !

If the dipstick is not "seated correctly" , as in not pushed down far enough , it will show less oil (a lower reading on the stick) than is actually in the engine . If you fill it to the full mark with the dipstick not all the way pushed in , the engine will be OVER full of oil and this could lead to both the smokescreen you describe and the low oil pressure as the too full crankcase of oil is whipped into a foam by the crankshaft .

Get the stick installed properly before you ruin this engine due to overfilling the oil .......

PS , in the bad ol days when an oil check went with a fillup at the "full serve" gas stations (drivers were NOT allowed to touch the pumps in those days , only the attendant could) , not pushing the stick all the way down was a way for crooked attendants to sell more oil . It was called "Half sticking" and would make it appear to the customer that the oil was lower than it actually was , and so another quart of oil would be sold . This was advantageous to a crooked attendant who was being paid a per centage of the sales rather than an hourly wage ....

 

My apologies, my question was posed as " If my dipstick was not seated correctly AND I DIDNT KNOW IT, I would add more oil to because of increased height of the stick, right?"

Too much oil = low oil pressure?

 

Glad we got the dipstick thing cleared up .

And yes , it's true , if you overfill the oil with enough for the crankshaft to be in a standing level of oil (a quart and a half to two quarts overfull is usually enough) , the crankshaft will whip the oil into an airy foam that doesn't pump well through the oil pump nor lubricate well at the bearings where it is needed .

I know it may sound crazy , but the only thing worse than too much oil is too little

 

So then what would cause 60+ PSI on the stock gauge after an oil change filling it to where the stick says it should be?

 

Getting past the likely error in actual reading , as in when it read 60 it actually could have been lower due to our gauges being notoriously inaccurate , what usually happens when it's over full is this ;

It will start and run with good oil pressure , for a little while . It takes a minute or two for the oil to become foam and then the pressure begins dropping . The foam will return (somewhat) back into oil again when the engine is shut off and the same thing happens again the next time it's started .

 

Oh , I almost forgot , The overfull condition causes the smokescreen cause the excess of oil being slung around by the crankshaft makes it's way past the rings (especially if they're a bit worn) and burns along with the fuel in the cylinders ....