Oil pressure 101

General Discussion
1

what is normal oil pressure on gauge. what wrong if oil pressure is to low. what wrong if oil pressure is high.

2
what is normal oil pressure on gauge
Depends on the engine, RPM, temp etc. and you would need the shop manual for that engine.
what wrong if oil pressure is to low.
Could be any of a number of things.
what wrong if oil pressure is high.
Could be any number of other things.

We need more info if you want any guesses. When is the pressure low, high? Year, engine, mileage? Sorry if you didn’t get the answers you are looking for, but based on the info you gave that’s what I have.

3

Back in the “Good Ole Days” normal oil pressure on a warmed up engine was 15+ psi at idle and 45+ psi at 2,000 rpm. Engines these days run higher pressure, 45 psi at idle and 75 psi at 2,000 rpm more or less. Oil pumps have a reliefe valve to prevent excess pressure when the oil is cold and thick and maximum pressure is limited to well below 100 psi in every engine that I have ever manually tested.

Low oil pressure results from a worn pump, a relief valve stuck open or worn components that bleed off pressure. Excessive pressure results from a relief valve stuck closed.

Are you having a problem or just curious?

4

oil pressure at idle is 45 psi? true all new cars use 0 weight oil now but has the bearing clearance changed that much from yrs past?

5

Sounds high to me,excessive oil pressure can ruin the "inserts"
In the good ol’ days after idle,it was 10 psi extra for each 1000 rpms there after.

6
oil pressure at idle is 45 psi? true all new cars use 0 weight oil now but has the bearing clearance changed that much from yrs past?
0W oil has little bearing on oil pressure. When you see something like 0W-20 or 0W-30, that first number is the cold oil viscosity index and cold 0W oil has a higher viscosity than hot oil with a viscosity index of 30. Those numbers are the viscosity index, not the viscosity. Viscosity changes with temperature and is measured in units such as SUS (Sayboldt universal seconds). You can have thinner than 0W oil, I'm not sure what such oils will be designated as if they come into use.

A relief valve in the oil pump is there to cap the oil pressure at a specific amount at high rpms or cold oil. Without it you can sheer the oil pump drive shaft.

I’m wondering if the oil pressure relief valve will be replaced by variable displacement oil pumps that automatically reduce the piston travel of the oil pump in response to high oil pressure in the future. Constant pressure hydraulic pumps for presses and other stuff are already working that way. The power needed to drive the oil pump is one of the parasitic losses in an engine and a variable displacement pump is one way to minimize that loss in our quest for better mpg.

7

My 20 + year old 4afe equipped Corolla has no oil pressure gauge, only an idiot light, so I don’t know what it actually measures. But the specs say a minimum of 4.3 psi at idle, and 36 to 70 psi at 3000 rpm. At normal engine temperature.

My 40+ year old Ford truck has a gauge and – can’t vouch for its accuracy – it reads between 40 and 70 psi pretty much independent of rpm, even at idle, once the engine is warmed up.

8

It’s been a long time since I’ve had a car with an oil pressure gage… and I installed that one.