How does oil pressure work?

[lt1man]

Let's say your bearings are worn on, does your oil pressure drop? What causes the oil pressure in your engine? Yes, oil pump sucks oil and causes pressure. But where is the oil pressure sensor located to determine what pressure?

If someone wanted higher oil pressure without changing grades of oil, what would they do?

 

[eljefino]

Well it depends. Some oil pressure sensors are at the other end of the crank, and some are right by the pump. Also depends where the bypass is, but it's usually by the pump. German cars like to pump "dirty" oil through the bearings then it goes through the filter.

If your bearings are worn, yeah, more oil leaks out. This might not make a difference if the bypass is still partially open.

 

[MolaKule]

The oil pressurization system in an automobile engine is a hydraulic system.

Pressure is Force divided by area. An external gear type oil pump takes a rotating force from the engine and progressively sqeezes the oil between the teeth of counter-rotating gears.

The force is constant but the area decreases, so the pressure at the outlet of the pump increases.

http://www.pumpschool.com/principles/external.htm

 

[Donald]

The oil pump itself has a mechanical relief that dumps enough back into the pan to prevent excessive pressure. Its spring loaded so not really effected by RPM. Nothing to do with the oil pressure sender or sensor.

But its not really a regulator but rather a relief.

If the spring were really tired, it might dump oil at a lower pressure and the measured oil pressure at the filter would be lower.

If the bearings are worn, too much oil will spray out of the bearings and thats not a good thing as too much will get on the cylinder wall, not all of it gets scrapped down and you burn oil.

 

[Rick in PA]

Basics: there's a little pump connected to the engine, it's a positive displacement pump, it's going to pump oil no matter what. The higher the engine RPMs, the more oil it pumps and the higher the oil pressure becomes.

There's a little spring loaded relief valve to keep the oil pressure from getting too high. At some point, when the oil pressure is high enough, the pressure relief valve starts to open and dump the excess oil back into the pan. This keeps bad things that can happen with too much oil pressure, from happening.

All this oil pressure is filling little passages (they're like tubes formed in the engine block casting). The little passages connect to the various bearings for the crankshaft and cam shaft. The whole point is to pump oil between the journals and bearings so no metal-to-metal contact occurs. As the oil sprays out from the bearings, it lubricates other things, like the cylinder walls and cam lobes. Then it goes back to the sump.

Oh yeah, there's an oil filter in there somewhere.

As the bearings wear, they become "sloppy", the oil sprays out from them more easily. The oil pressure can not build-up like it can on a nice, tight, new engine. If the engine is old enough, and tired enough, I suspect the pressure relief valve will never even open. If the engine is old enough, and tired enough, like your buddies' car back in high school, the oil pressure light may occasionally flicker on at idle, 'cause the oil's "leaking" out of the bearings faster than the oil pump can pump it in. "Hey, your oil light's flickering"... "Um, yeah... it does that."

 

[boosted]

Is it true that using a smaller oil filter can increase the oil pressure?

 

[lt1man]

Ahh, got it. Basically the thickness of the bearing acts as a regulator sorta. That explains it.

 

[Rick in PA]

Originally Posted By: lt1man
Ahh, got it. Basically the thickness of the bearing acts as a regulator sorta. That explains it.

Yup, you got it. Bearing clearance controls the back pressure, until the pressure relief valve kicks in.

 

[bruno]

Uh , no the oil is pumped through the filter to the bearings .
No way it can go from the bearings to the filter directly .

 

[eljefino]

Originally Posted By: bruno
Uh , no the oil is pumped through the filter to the bearings .
No way it can go from the bearings to the filter directly .


Uh, sure! Read http://www.w124performance.com/docs/mb/other/SAE_OM617.95X_Development.pdf

pages 12-13. The Mercedes OM617 (for one) pumps oil through all the pressure galleries up to the filter, from where it dribbles back down into the pan and the turbocharger, the one spot where the engineers feel that absolutely pristine oil is necessary.

 

[TFB1]

Originally Posted By: lt1man


If someone wanted higher oil pressure without changing grades of oil, what would they do?


IF the engine has worn bearings, oil pump, etc the components should be replaced but higher viscosity oil will increase pressure, though only slightly...

For performance type engines high volume and/or high pressure pumps are available... While either will generally increase pressure, the high volume usually spreads the increase across a larger operating range...

Originally Posted By: boosted
Is it true that using a smaller oil filter can increase the oil pressure?

Nope... But I have seen some filters that gave a slight increase in pressure from others... In the old days(I'm talking 35+ years ago) when the Motorcraft filters were packed with fiber type material, they would always give 4-5psi increase over a paper type...

 

[gotib007]

Hey, I seem to recall that aircoooled VWs used a piston and spring setup as their oil pressure relief valve, and that you could either vary the spring stiffness or shim up the spring to monkey around with the oil pressure. Am I imagining that?

 

[bruno]

From the filter to the engine bearings with a branch to the turbo .

 

[mechtech2]

With worn bearing, oil pressure in an engine drops [at operating temperature].

Oil pressure sensors vary in there location.

Thicker oil is the oldest trick in the book for raising oil pressure on worn engines. Modern engines don't wear as fast or as much with today's oils and better design and manufacturing.

Another type of pressure besides the oil pump in your engine is a phenomenon that happens in plain bearings. As the part rotates, it build up oil in a wedge, and increases pressure right where you need it. Called a hydrodynamic wedge. without this effect, engines would not run!

Consider lawn mower engines with no oil pump - the splash and hydrodynamic wedge is what makes them run and last.

And Chevy did not even have oil pumps on cars until 1955! Sounds astounding, but true.

 

[bruno]

My 49 Chevy had an oil pump and it fed the main bearings and the trough the rod bearings picked up their oil from . Hot running oil pressure was 15 psi .

 

[morris]

"And Chevy did not even have oil pumps on cars until 1955! Sounds astounding, but true." maybe it DID have a pump, but did NOT have a full flow system. i think. it was a LOW pressure system. allso called a splash system.

 

[morris]

"And Chevy did not even have oil pumps on cars until 1955! Sounds astounding, but true." maybe it DID have a pump, but did NOT have a full flow system. i think. it was a LOW pressure system. allso called a splash system. i think.

 

[morris]

i looked up some info, i was wrong on the oil pressure. it looks like it is 10-15 psi. that was just the 20 th time this week my brain failed me. but the last time i read that it was over 40 years ago.

 

[morris]

i looked up some info, i was wrong on the oil pressure. it looks like it is 10-15 psi. that was just the 20 th time this week my brain failed me. but the last time i read that it was over 40 years ago.

 

[TFB1]

Originally Posted By: bruno
My 49 Chevy had an oil pump and it fed the main bearings and the trough the rod bearings picked up their oil from . Hot running oil pressure was 15 psi .


Correct, oil was also pressure fed to the rocker arm assembly on top of engine...