Topic: General qustion about oil pressure, flow, viscosty, etc.

[grumpy]

Why is "high" oil pressure good?
For example, there's the 10 PSI per 1,000 revs rule - why is 60 PSI at speed better than, say, 10 PSI.
Pressure is resistance to flow, right?
Flow increases as pressure decreases.
So if given that your oil tank is full, why wouldn't a lower pressure, via perhaps a lower viscosity oil, mean that you've got more flow?
More flow is good.

So what am I missing here?

[dave500]

the more work an engine is doing the more the pistons are trying to push the crankshaft onto the pavement,higher oil pressure keeps the crank floating on oil between the bearings,if its low itll get squished out and have metal to metal contact.,pressure and flow both increase as you pump harder.

[grumpy]

OK, I get it.
If it was just a matter of flushing the max amount of oil through the system to keep everything cool then low pressure / high flow would be good.
But since we're using to actually lube stuff then we need pressure to keep the oil jammed in between all the expensive metal bits. So to speak...

[dave500]

pistons/cam lobes/rocker gear/transmission are splashed,,the oil pressure is used to circulate to the top end aswell as "float "the main and big end bearings,,it oozes out the sides.

[Pecantree]

The Natural science museum in Houston has a Kugel Ball sculpture right outside.

Explained here:https://en.wikipedia.org/wiki/Kugel_ball
These things have a large pump, I think 5 or 6HP. And the gap between the ball and the cradle is thinner than a credit card.
This is the same principle as in our engines or the turbines in hoover dam.
They are fun to play with
Steve

[magconpres]

Flow increases as pressure decreases.

This isn't right, or at least not the entire picture.
This says that if pressure goes to zero, flow is infinite.

Pressure build up in a fluid is a result of the forces applied to the fluid.  Some of that force is from the pump and some from the constraints of the container.
If the force goes to 0, then there is no pressure and no flow.

I'm not an engineer, but it seems that maybe what we are really after is a sufficient flow of oil at the bearing surfaces and other lubricated areas and not necessarily pressure.  Pressure is probably just easier to measure, and given that everything else is relatively constant (oil passage cross sections, oil viscosity) serves are a proxy for flow.

I suspect you could put really thick oil in your engine, have high oil pressure, and still damage the engine due to insufficient lubrication.

[Markcb750]

The oil pressure increases as the engine rpm increase because the pump is driven from the motor and pump flow is directly related to pump speed.
Theoretically a pump moves 6x more oil at 6000rpm then it does at 1000rpm.   

Pressure increases because more oil is being pushed through the lubricating orifices as engine rpm increases.
 

There is a relief valve in the oil supply system which limits the maximum pressure by dumping oil back to the sump. 

A more detailed explanation is available here.  http://en.wikipedia.org/wiki/Hydraulics