Thread: Oil Pressure

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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.

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.