Thread: Oil Pressure

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Need some help on what to do about my oil pressure. When I first crank up I have good oil pressure even driving oil pressure is good.After it warms up and you stop pressure will drop to around 10 or a little less, but soon as you touch the gas to will go right back up to good pressure. I am going to put a manual gauge on just to see if my other gauge is working right. I'm looking for some insite?

Isn't that the way it's supposed to do ? My '62s gauge increases as the RPMs increase. Up to a point that is !

I't just looks like 10 or less on oil pressure at idle is to low

hmmmm, could be the gauge but there are lot more knowledgeable members here to answer questions such as that

are you running a SBC ?

Are you running a crankcase vent? I'm not sure why, but I was running a PCV on one valve cover seeing the same thing, and when I put the vent on the opposite side my oil pressure at idle improved. That can also point towards bearing clearances being on the wide side, too.

No crankcase vent, engine is a 383 stroker

Mine's a 347 stroker, SBF. You might try a vent in your oil fill port and see if you get any change in your pressure.

depends on where you are reading pressures-----in an engine with sealed crankcase and drysump or possibly just a vacume pump, the oil pressude normally seen on the guage will be result of differential pressure/vacume of oil pump and crankcase vacume------


One of the recent 1400hp 500cid we ran with 5 stage pump had so much vacume from the scavage side that positive pressure reading could/would go toward zero and turn on a 5 psi low pressure warning lite !!!!!!!!!!!


There was enough suction that I actually believe that we didn't even need the positive pump stage---coulda let the scavage pull the oil thru----------

You didn't say what engine you have, but that sounds like normal for a stock gen 1 chevy small block, and even with a relatively well built (hot rodded) one, it is still normal. A lot depends on the clearances built into the engine at the time it was built, and the type of pump and oiling system it is running. For a stocker, it's just fine; I have never had one that was different in stock or near stock form, and never grenaded one, even drag racing. This subject sometimes gets a lot of play here, and there are situations when one might want, or need more pressure, or volume, but for a stock engine with normal clearances, yours is doing what is should.

Rule of thumb is 10 lbs per 1000 rpm hot.

Engine is SB 383 stroker 460 hp I got it from Enging Factory got bout 6500 hundred miles on it.

I would say you are plenty good. You have to get into the realm of forced induction and nitrous, or really radical cams and high volume intakes and high revs before you will out power the stock oiling system. Think about what is going on in your engine: You start it up cold for the first time one day, and the clearances are perhaps a wee bit tighter than they will be when it is at operating temp, and the oil is more viscous, so the startup pressure will naturally be somewhat higher than when it is warmed up, say 30 to 40 psi. As it warms at idle, the pressure starts dropping, you head on out, and it gets right up to normal pretty quick, but at an operating speed of somewhere around 3000 to 3600 rpm, the pressure will be about 30 to 50 +/-. You come to a signal and slow down, and the pressure starts to drop because the oil pump is slowing down; but the engine isn't working as hard, either, and doesn't really need that high oil pressure, so at idle, somewhere around 700 to 900, it will settle at around 10 to 15. When you start accelerating again, the reciprocating and rotational forces begin to require more oil pressure, and since the pump is starting to spin faster again, the pressure goes back up. Also, consider the area of a bearing, for example, the pressure in the oiling system, and do the math. Even at 10 psi, a bearing with about 9 square inches of area will have almost 100 pounds of supporting pressure in it; and at 40, 400. That's a good amount of support for that rotating surface.

I can't remember the term for it, but a rotating bearing operating at its design speed, and with correct bearing clearances does not really need the pressure of lubricant being forced between the bearing surfaces internally to operate quite efficiently; all it needs is a constant source of oil getting onto the rotating surface, and it will actually draw the oil into the bearing once the shaft is turning at its normal speed, and thus, keep that cushion of oil in the bearing. I used to work on some very large electrical machines that the rotating elements weighed in excess of 50 tons. They operated, in normal operation under varying loads without the oil pumps being on; there were slinger rings on the shafts just outside of the bearings, and they slung oil around inside of the housings in a mist and it was drawn back into the bearings. The only time we put the high pressure oil pumps on was at startup, and shutdown, to lift the shafts off of the babbits until they were rolling at speed, and hold the shafts up off of the babbits until they had stopped moving. So, oil pressure is something that has a lot more to it than we usually consider.

Like I said, I hadn't really thought about the "why's" when my oil pressure improved with the crankcase vent but Jerry's post made me realize that all I was seeing was a change in the indication, not the actual pressure. At idle I was pulling a vacuum on the crankcase, and my gauge was indicating about fifteen pounds. With the breather the indicated pressure rose to between twenty and twenty five which makes perfect sense. The pump was delivering at the same pressure, but the indication was looking at the overall pressure across the pump and without the breather my suction head on the pump was right at negative eight pounds, 16 inches of mercury. Pull your oil filler plug and see if you idle oil pressure jumps up, then decide if you want a breather or not.

Originally Posted by Rrumbler

I can't remember the term for it, but a rotating bearing operating at its design speed, and with correct bearing clearances does not really need the pressure of lubricant being forced between the bearing surfaces internally to operate quite efficiently; all it needs is a constant source of oil getting onto the rotating surface, and it will actually draw the oil into the bearing once the shaft is turning at its normal speed, and thus, keep that cushion of oil in the bearing.

Hydrodynamic lubrication is the term.............good on you for knowing the principle.

The amount of pressure read is meaningless in and of itself. Yeah, there's a popular belief that higher pressure means better lubrication. Bunk.

A change in indication IS a change in the actual pressure.

Your pressure guage indicates relative to atmospheric pressure.

The crankcase vacuum added algebraicaly against the oil pump output reducing the output pressure relative to atmospheric pressure.

By venting the crankcase, you reduced parasitic load of the pump, increasing its efficiency, and increasing the output pressure .