Oil Pressure Decreases as RPMs Increase

[90cummins]

There are 2 possible reasons for this both of which are not issues;
First you could try using a lighter oil, if the oil is too heavy at higher speeds the oil may be slow flowing into the pump causing minor cavitation, (starving the oil pump).
Second possibility was mentioned earlier and that was the pressure relief opening at higher speeds to relieve excessive pressure/flow.
I've seen this on some of my equipment all of which have no mechanical issues.
Sometimes knowing what's going on can be a bit concerning!
90cummins

 

[Soundguy]

I'm with 90C.

What oil is the Op using. If excessively thick, could be standing the relief open at rpm.. Relief might be a hair weak spring.

Gauge good?

 

[Industrial Toys]

Maybe with more oil in circulation in the top end of the motor at higher flow rates, there is simply more air in the oil effecting the reading. Plus the oil is being churned up more by the faster crank.

 

[California]

... oil is being churned up more by the faster crank.

That suggests the oil might be overfilled to where the crank is striking it.

 

[Jtullis13]

I'm on board with 90cummins. I have a 2210d refurbished from Fredrick's, & I have the exact same thing happen with mine. 40psi at idle & 30-35 while operating. I don't hear anything out of ordinary while operating it. It's been like that for 20 hrs or so since I installed the gauge. The oil level is right on the full mark & I'm using 15w40. Oil gets thinner as it warms up and should flow better, so still guessing pressure release valve. But that's just my opinion.

 

[231S]

Mine is a Fredrick's refurb also, and I've got 5 quarts of Rotella 15-40 in the crankcase.

The gauge is a Bosch brand from Advance Auto, but I have not checked it with another gauge. I feel like it is working showing the relative pressure changes but may be off on the actual pressures. If mine and Jtullis13's gauge were reading 10psi low then we'd be in the spec of 35-50 psi at all times. No rpm is specified on the oil pressure spec.

I have done some reading on the marine engines on the sailing and cruiser forums and I've seen it mentioned that Yanmar seemed like they were more worried about the high side pressure than the low side. This makes sense given that the low oil pressure light doesn't come on until it gets down around 10 psi, or lower according to some. Given that both Jtullis' and mine idle at 40 psi, if that relief valve didn't open then the pressure would be way over spec at operating rpm.

Jtullis is the fourth 2 cylinder Yanmar that I've heard of acting this way, including mine. I would bet a good many do, but so few have oil pressure gauges on them it just isn't seen all that often.

Maybe this thread will help someone if they install an oil pressure gauge and see the same behavior, when they were expecting the oil pressure to go up with rpms.

Thanks for all the replies, fellas.