Oil Pressure how it works ?

[Yannick]

Hello,

My question is probably rookie but I ask ;

Can we say the higher oil pressure is ,the better is ?
I have a boat with a 5.7l engine. When I run it at 4000RPM the oil pressure is around 460. Engine boat is working hard at 4000.

My main question is what is the goal of the oil pressure gage and how it works?

thanks

 

[440Magnum]

Oil pressure is an indirect measurement of how reliably oil is being delivered to the bearings. So long as there's enough pressure to provide a steady flow of oil to each bearing, adding more pressure doesn't do a whole lot of good. It might improve cooling of the bearing, but its a tradeoff because pumping the oil up to higher pressure also heats the oil.

Its also a direct indicator of possible problems- internal oil leakage, a collapsed or blocked filter, blocked oil pickup, or excessive oil temp causing thinning of the oil can all show up as lower than typical pressure. But "lower than typical" is a key part of that- different makes/models of engines have different normal pressure vs. RPM profiles anyway, so absolute oil pressure is only meaningful in comparison to what is "normal" for a given engine at a given speed and oil temperature.

 

[Nick1994]

More does not equal better. There's an optimal range for everything. Oil pressure of 460? 460 ounces per square inch? That would be 29 psi Lol

 

[Clevy]

Originally Posted By: Nick1994
More does not equal better. There's an optimal range for everything. Oil pressure of 460? 460 ounces per square inch? That would be 29 psi Lol



Kilopascals.

 

[440Magnum]

Originally Posted By: Nick1994
More does not equal better. There's an optimal range for everything. Oil pressure of 460? 460 ounces per square inch? That would be 29 psi Lol


kPa.

 

[Yannick]

Correct its 460kpa I read on my gage.

 

[Falken]

It is a positive displacement pump.

Two gears mesh and deliver the same quantity of oil regardless of thickness.

It is the speed of delivery that is different.

The more resistance the higher the oil PRESSURE.

The less resistance the greater the oil FLOW.

Low oil pressure of the same weight of oil for comparison can indicate worn bearings or oil pump gears, or a pressure relief valve is bypassing too easily.

People with a really worn engine may benefit from thicker oil to build pressure in looser bearing tolerances.

Higher flow that is in the recommended oil weight for that engine is desirable as lubrication is delivered to the top of the engine faster in cold temps.

 

[Clevy]

Originally Posted By: Falken
It is a positive displacement pump.

Two gears mesh and deliver the same quantity of oil regardless of thickness.

It is the speed of delivery that is different.

The more resistance the higher the oil PRESSURE.

The less resistance the greater the oil FLOW.

Low oil pressure of the same weight of oil for comparison can indicate worn bearings or oil pump gears, or a pressure relief valve is bypassing too easily.

People with a really worn engine may benefit from thicker oil to build pressure in looser bearing tolerances.

Higher flow that is in the recommended oil weight for that engine is desirable as lubrication is delivered to the top of the engine faster in cold temps.


A positive displacement pump flows the same volume of oil per revolution so it doesn't matter if you are pumping 3 in 1 oil or sae 70,the pump moves(flows) the exact same volume of oil.
Pressure is the only metric affected. So your mostly right other than the more flow part.

 

[440Magnum]

Also, engine oil pumps are only QUASI-positive displacement. There's a pretty high leakage past the gears or gerotor(*) tips and end-plates, especially at normal operating temperature. And since the pressure relief valve is typically upstream of the filter, many vehicles transition to a constant-pressure source (where 'source' is the combination of the pump and relief valve) at higher engine speeds.

Of all my vehicles, only the Jeep 4.0 has a gear type pump, the rest are gerotor pumps similar to this (although the rotor shapes are different):

 

[MolaKule]

It depends on where it is measured but 207 to 450 kilopascals of pressure is more than sufficient.

Oil pressure is the pressure (force on fluid divided by the area) of the oil provided by the pump above atmospheric pressure so that a viscous fluid will move.

Oil pressure depends on the viscosity of the oil, bearing clearances, oil hot or cold, condition of pump, filter bypass valve, pump bypass valve, and engine rpm.

Oil flow in an engine is primarily used for cooling and filtering.

It is the oil/additive package that provides the oil film for lubrication and protection.

Secondarily, the oil pressure can be used for Variable Valve Timing.

 

[Yannick]

Can thinker oïl increase oïl pressure? and vice versa with thinner oïl?

 

[Jetronic]

The maximum oil presure is dictated by the pressure relief valve, but other than that a thicker oil will generate higher oil pressure for a given rpm.

What the oil pressure gauge is useful for is seeing when it's time to change the filter. If the maximum oil pressure drops about 100 kpa below what it was with a new filter, the filter medium is full and require changing of the filter..

You can also use the pressure gauge to see when the oil (and engine) are up to temperature, or when the oil is getting too thin (from excessive heat or fuel contamination etc). Slow down if the oil pressure is dropping significantly from where it normally sits.