Boost II

iTrader: (1)

OK thought about it a bit more - must be to do with the resistance to flow, like water pressure or blood pressure. Is this right - too low a pressure and the oil will not circulate the engine - too high a pressure could mean a blockage somewhere in the system?

So if the engine is turned on I would expect oil pressure would go from nothing, to being high as cold oil is viscous and then lower as things warm up and it can flow more readily. Or would pressure go up more as the oil expands when it gets hot?

[Edited by Boost II - 6/5/2002 1:25:55 PM]

Boost II

iTrader: (1)

What is oil pressure? (As I understand, you can't compress a liquid and oil is not volatile, so what actual pressure is measured and what does it tell you??)

IanA

I'm not a scientist, but I think this is the gist: Pressure is the force exerted over a certain area by something rather than how much the thing is changed in state or size (eg compressed). So 35psi in a tyre is like putting 35 pounds of lead on one square inch of rubber on the floor.

The pressure in this case is the force transferred through the oil by the oil pump to the internals of the engine. The oil also expands when it is heated so it increases the pressure.

The purpose of the gauge is the same as the temperature gauge, to help prevent or indicate engine problems. If you look at the temp gauge it usually stays in the same bit in the middle, maybe climbing a bit in very hot weather or traffic. So if the needle was too low you'd think that the thermostat might be gone and if it was too high you'd know the engine was overheating. The Oil pressure gauge would also have a normal range, too low and it either needs more oil or there's something wrong, too high and you've overfilled it and risk blowing some of the seals or there's something wrong! Either way you know to take it easy and seek medical advice.

I'm sure someone can explain it better than that, but hope it helps

MarkCSC

I have an oil pressure gauge in my Porsche. When I start it up the gauge reads anywhere from 6-8 bar in normal driving. After a while the car heats up and the pressure drops to 5-6 bar.
So from my very unscientific experience viscosity has more effect on pressure than expansion of the oil.

Mark