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Rb25det Oil Pressure Question

gomer23
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gomer23 Rookie

gomer23

Posted
Posted

Maybe you guys can shed some light on this subject for me.

I got my car back together a couple months ago and have noticed something with the oil pressure. I have a 1989 Nissan 240sx with a RB25DET swap. Once the motor is all warmed up I am seeing oh Idk 7-10psi of oil pressure at idle and crusing at 2500 rpms it seems to be around 20-25psi. The part that worries me is anything past about 4k RPMs the pressure seems to peak at 40-45psi or so and doesn't go up anymore. Right now I am running conventional 10w-40 oil. I had some 10w-30 Mobile 1 synthetic in there and it did about the same thing. I did replace the oil pump about 2,000 miles ago or so with a new OEM one. I just recently took off the oil pan and replaced the gasket around the oil pickup as well.

Is that oil pressure normal? Shouldn't it build more pressure in the higher RPMs? If you need any other information let me know. I am going to try swapping to a mechanical gauge here in the next day or 2 just to be sure its not that. But when the engine is cold the pressure will climb to 70psi until the oil warms up.

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https://www.sau.com.au/forums/topic/324132-rb25det-oil-pressure-question/
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tiberis Enthusiast

tiberis

Posted
Posted

from the R33 engine manual:

RB25DET=

@idle RPM ~1kg/cm2 == ~14psi

@2000 RPM ~3.5kg/cm2 == ~49psi

@6000 RPM ~5.6kg/cm2 == ~80psi (which is about the same as the pressure on a diver at ~56m under water)

when cold my engine goes a bit above 80psi before it warms up. i would double check with another gauge first though, if you are using the stock in-dash one it's known to be a bit inaccurate. but those numbers do seem a bit low.

Kinks Grand Master

Kinks

Posted
Posted

oil viscocity makes a huge difference to oil pressure. a 10W30 will be higher pressure when cold than a 0W40, but the 0W40 will maintain a bit more pressure when hot.

pressure is simply a measure of restriction, it is a combination of the "gaps" in your engine that oil is forced through (larger gaps = less restriction = lower oil pressure) and oil viscocity (lower oil "weight" = less restriction = less pressure).

the stock gauge is very slow to react so unless you can hold at a certain RPM for a while I wouldn't trust it.

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