Oil pressure reducing with RPM
 

As above, problem started this morning. Car is a 1995 WRX.

Oil pressure reduces when increasing RPM. At cold idle, gauge was above the 100psi gauge maximum, when I would rev it to 3k or so, the pressure would suddenly drop - almost to zero. As the car warmed up, the RPM at which pressure would drop kept on rising. By the time the engine got warm (40psi idle oil pressure), the oil pressure was dropping at around 4k RPM. It would increase from idle and then start dropping back at about 4k.

It would do this both in gear and in neutral. I checked oil level, it's ok, just a little bit over the full mark. The dashboard oil light did not come at all during all this.

I changed the oil filter and oil (15w-50 semi-synth) last week.

Has anyone ever seen a similar problem?

could be a faulty gauge, but i wouldn't rule out the oil pump could be failing, if u din't have gauge u wouldn't know this problem was there and would drive the car normally because u would trust that u have oil in engine and the fatory light is not on, so check all connections on your gauge and look for and leaks around where it is fitted.........mark

No leaks and the electrical connection is good. I'm hoping that the gauge/sender is faulty too.
I've just got an idea, I can probably rig up a ghetto test where I remove the oil pressure sender and with the flexible oil pipe it bolts onto pointing into a container, start the car and do a quick rev to see what happens. With the way the gauge was going to 0 psi oil pressure, I think I should be able to see this visually if there is indeed an oil pressure problem.

Dont do that manual test. Rig up a mechanical gauge instead.

Duncan,

I guess the reason why you are telling me not to do the test is because with the oil flowing out of the pipe freely, I will now have truly little oil pressure?

The pipe to the oil pressure gauge has only a 2mm hole through it, would that help?

I don't have access to mechanical oil pressure gauge but I do have a boost gauge that I'm not using or planning to use in future and I could possibly use it for this test.

dont use a boost gauge the readings could be wrong and if its a mech boost gauge i defo wouldnt use it. the only way you will know for sure whats wrong will be to do as dynamix has already said and get a mechanical oil pressure gauge/tester on it, i had this prob with mine not long ago and it turned out to be a knackered oil press sender but until you test yours with the correct equipment you wont know what it is.

I think duncan is saying that because (correct me tho if im worng) if you havent got pressure switch in the oil wont be under pressure and there fore will go easiest route (eg pipe into container) which then means lack/no oil supplied around the engine components???

Then leading to component failure.

Any decent garage can do an oil pressure test.

Thanks for all the replies, I will attempt to test this based on the suggestions and report back when I get to the bottom of the issue.

Found the problem. It's with the sender, once it reaches the max pressure that can show on the gauge, it starts going back to zero (as it was behaving on the car). Tested with an air compressor connected to gauge sender.

There's a lot to be said for the good old mechanical gauges! In over 11 years of using them (Mocal) I've only ever had one oil temp. sender problem and no probs with pressure or boost

JohnD