Oil Pressure

[christo]

I have a 2006 Duramax with oil pressure that seems a little on the low side.
About 36psi @2000rpm.
What I find really strange is the oil pressure will drop 3-4 psi when going from a light load to operating under a heavy load.
I first noticed this while pulling a 14k 5er in tow haul/haul mode.
There would be very little change in engine rpm while this pressure change
takes place.
Anyone have an explanation?

CHRISTO

[JohnC]

My bet it the oil temperature is going up. Thinner oil -> less pressure.

That said, 36 psi is plenty at 2000 RPM, and the gauge is not the most accurate, either...

[Quack_Addict]

My `06 LBZ shows similar oil pressure to what you note. The `06 LBZ truck I test drove before I ordered mine also showed what I consider 'lower than normal' oil pressure.

There was a post on here about a month back regarding the oil pressure in LBZ engines and pretty much everyone that responded noted similar oil pressure to what you noted.

I guess if you follow the old rule-of-thumb of having at least 10 PSI per 1000 RPM, we're all good.

[LanduytG]

My LLY runs 45psi under heavy load when hot out. Colder temps os about 50psi. Nothing to worry about.
Greg

[christo]

Thanks for all the replies.
I'm still wondering why the oil pressure drops 3-4 psi under increased accelerator then increases when I take my foot off.
This is most noticable when pulling a load and the RPM has not really even changed yet because of the load.

CHRISTO

[JohnC]

I'm still wondering why the oil pressure drops 3-4 psi under increased accelerator then increases when I take my foot off.

That's a good one. I missinterpreted your original post. I thought you meant that pulling a big load netted lower pressures than driving empty. First thing I'd do is check the gauge. Unless you're pulling so hard the oil pump is sucking air... ;)

[imsweetdaddy]

mine is around 36 psi at idle, but jump up to 60 at 1000rpm and nearly pegs out at 2k rpm and Ive got over 232k mi. What brand of oil and filter are you using? Any additives? What's the pressure at idle? What's your temp running? You can e-mail me at ImSweetDaddy@aol.com. I'd be glad to write you back about what my suggestion is.

[SoTxPollock]

christo, this is my guess since I don't know for sure where the oil hole in the crankshaft is in relation to the piston location on the Duramax. When under acceleration the only thing that keeps the crank bearing from contacting the crank journal is the thickness of the oil film. Realizing that all engines have bearing clearances between those two parts, that puts the bottom portion of the rod bearing on a particular cylinder farther away from the crank surface and of course each one in succession which leaves a larger gap for the oil to escape from the bearings. When you take your foot off it unloads the load and only the compression pressure is being applied to the bearings and not the full power fuel burning pressure. Thats one part, the other is that the same thing happens to the crankshaft at its location in the main bearings. When your got it pulling hard its pushing toward the bottom of the main caps allowing more room at the top half of the bearing that is in the block. When you let off everything for all practical purposes of discussion centers back up and those clearances close back forcing the oil to travel through a smaller passage and thus the slight increase in pressure as seen on your gauge. The more the clearance the more change one sees. Its not a problem, its always been that way, the real key is oil volume being flowed to keep the surfaces cooled. Pressure has a lot to do with other factors of the fluid itself and I don't have time to go there, but the 10psi for every 1000 rpm was used under racing conditions and proven reliable so not to worry. Just drive and enjoy it.

[christo]

Thanks to all for the good info.
A special thanks to SoTxPollock for your good perspective.

Christo