Patrick66":3kdv0ppt said:
my oil pressure has been concerning me since i rebuilt my engine, with the mechanical gauge hooked up i get 20-25psi (in park with the engine from idle to about 2500)....
It'll probably only last another 200,000 miles or so, after that you may need to start worrying. I wouldn't lose any sleep over it.
The only thing an oil pump really does is to deliver the oil to its destination. The actual instantaneous pressure between the critical parts such as bearings, etc. goes up to many thousands of PSI under load. There is no way that any oil pump is capable of reaching that sort of pressure, so a few PSI difference really won't matter so long as the oil actually got there.
Think about it; oil pressure is really only a product of RESISTANCE TO FLOW.
If you had an oil pump pumping through a straight, open pipe at a given speed, the only resistance to flow would be from pipe friction and whatever internal viscosity friction the oil has. The pump will only have to push hard enough to move the oil, so pressure will be quite low although flow will be high.
Now, put a faucet valve on the end of the pipe and close it just a little bit. This will cause the pump to work harder (assuming the same speed) so now there is some backpressure. The pressure inside the pipe goes up and the oil will squirt farther out of the pipe.
If we close the faucet almost shut, there will be a LOT of pressure inside the pipe, and the oil will really squirt a long way now. Keep in mind that an oil pump is a positive-displacement pump, and so long as the speed remains constant the volume will also remain constant. Trying to force the same volume of oil through a smaller hole will definitely raise the pressure.
Now, if we leave the faucet valve at the same setting but switch to a heavier grade of oil, we will have even higher oil pressure. This is due to the fact that "viscosity" is really just a way to measure an oil's "RESISTANCE TO FLOW". Thicker oil doesn't flow as readily as thinner oil. Using thinner oil results in lower pressure but it flows better and requires less power to get it there.
The oil pump in our engine really just sees a leak through which it can pump oil. The bearings, etc inside the engine add up to a somewhat controlled leak that remains fairly constant but the oil pump speed goes up-and-down with the rpm of the engine. The only thing that changes much is the viscosity of the oil as it warms up and cools down.
An engine that is really worn out certainly may need to go up a grade in viscosity to allow it to limp along a while longer but that is only delaying the inevitable.
Bottom line is so long as there is enough pressure to get the oil where it needs to be then you have enough. ANY MORE PRESSURE THEN "ENOUGH" IS WASTED ENERGY.
Thinner oil really can be better.
Joe
