Hey all, running into a very strange oil pressure issue that started for me at the end of last year. What happens is my oil pressure drops as engine load increases. Not just due to RPM. At idle I have perfect and stable 30 psi, always. When I do WOT in neutral if I rev to redline I get 60 psi at 3k and it drops down to 55 at 6k. Same story more or less in 1st and 2nd gear. However for 3rd, 4th and 5th gear it does not exceed 45 psi unless I am off throttle. This happens regardless if I am WOT or half throttle. If I am off throttle it will climb to 60 psi. When I am on throttle that pressure will reach 45psi and slightly drop at redline which concerns me. Last year I did rebuild my OMP due to it leaking and my oil pressure sensor due to it also leaking. Unfortunately don't have that old sensor, but the new one is good and working 100%.

The common cause for this is a bad front cover o ring, but my oil pressure doesn't change much depending on the temp of the oil. Also don't have low pressure at idle hot or cold. Mazdatrix states a small o-ring seal issue can cause pressure to drop to 45psi at high rpm, but again this only happens when I have more engine load not just due to rpm. If it's this issue my current plan is to drive the car till it actually gets worse and can be diagnosed clearly.

The other thing i could see it being is the OMP, which is tied to my oil system and the throttle and like maybe could be causing too much/not enough oil through? Again I couldn't find any posts or in the FSM about this being a potential problem. Anyone seen an issue there? There are no leaks at all so its not that.

The final cause I see could be that something blocks oil flow to the sensor/engine but that doesn't make sense to me because with no load the oil pressure is fine, why would less oil be present at the same PSI just due to load. Haven't taken the oil pan off ever and really don't see how that could be it, but yes I am aware that is a potential cause. Just don't really accept that in this case since I haven't been in there.

engine is all original, 161k miles, never rebuilt at least anytime this millennium. Any thoughts on a cause would be greatly greatly appreciated.

 

The OMP will not cause this. The o-ring might cause this, but since your engine is all original it seems a bit unlikely as the cause.

Are you measuring the oil pressure with the stock sensor? The gauges and sensors can be a bit wonky after all this time. Even if you replaced the sensor, the gauge is still old. And frequently the condensor on the harness goes missing which can cause unusual gauge behaviour.

In mine, I had "zero" oil pressure until 3k rpm and then like 25psi to redline. Then I replaced the sensor, and now I have normal pressure (better than normal actually, so I assume my mystery engine I bought has an upgraded regulator) except that when I turn the headlights on the gauge can float anywhere +/- 20psi around the actual reading.

Point is, the oil pressure gauges on these cars are suspect at this age. I would verify with a mechanical gauge before assuming you have an issue.

 

Yeah I probably will buy a new sensor or a mechanical sensor to test it. Seems weird to me that the sensor works normal at some points and not others, but everything else seems happy so I'll give it a shot. Thanks for the input!