Ok, so I am trying not to stress about my low oil pressure on my '91 TII streetported enigne with 1100 miles on it.

Warmed up oil pressure:
Idle 10 PSI
3000 RPM 50 PSI

Tonight I started the car and ran it to 3000rpm and held it there watching pressure and oil temp. The pressure dropped as the oil heated up. But it stopped at about 60psi. Then, the oil temp hit 160f and the presure dropped to a little under 50psi. This doesn't sound like that seal in the front cover.

I am thinking oil cooler or that thermostat in the oil cooler is messing up. Can a oil cooler fail?
Can the thermostat fail? (It has full oil and I have changed the oil filter with no visable oil leaks and no smoking)

That pronounced drop just seems like something is changing to cause that. The oil leaves the engine 4 times. Oil filter, Oil cooler, oil metering pump, and the turbo. It seems like the cooler would be a likly suspect. Any input on this?!?!
Thanks

James

 

Factory oil gauge or aftermarket? If factory, came with the car gauge, I'd start the experiment over with a aftermarket gauge. I would like to say though, that when I used the wrong gasket on the front cover a couple of years ago, it did just as you have described. I reassembled the cover using no gasket. Just rtv and a o'ring. Big difference. Never experienced a bad oil cooler yet(except the 82 that had the hairline crack on the fitting due to overtorque).

 

Hey James, I wish I could help ya about that cooler thing, but I'm not sure either...I know the thermostat can break, but I don't think thats what your was. I had a ? though...where did you get your 720cc injectors??? I need them for my GTR motor

 

Possible problems:
-eccentric shaft by-pass valve not closing when oil gets hot(should be fully closed when oil hits about 140F.Was this replaced/checked when motor rebuilt?
-oil pressure control valve/oil pressure regulator leaking or passing at low pressure.
-obstruction in oil lines to or from oil cooler.
-oil thermostat in cooler not opening,should be fully open at~150F.
-lousy oil pump
-gauge is wrong.
Assuming you are measuring the oil temperature in a good place,it would seem to me to be not to be the oil cooler.
-On both my cars the oil pressure goes up as the temperature increases from cold engine to warm engine,as the eccentric shaft by-pass closes.I woul star there.

 

?? my presure when cold is 75psi then slowly goes down as it warms up.

 

It is an autometer gauge (Ultralite procomp). It is mounted to a Racing beat adapter plate that goes between the engine and the oil filter.

The engine was built by Atkins and one of the things they do is remove that bypass so it runs the same oil pressure warm and cold.

I got my 720CC injectors from Rocky at RX7.com

 

most likely suspect is the front cover o-ring/gasket, oil pressure relief, or bearing clearance to large. oil cooler should not be a problem and oil pumps usually fail. what type and weight oil? If new motor I would contact the rebuilder for guidance so not to void any possible warranties.

 

According to Mazda,the regulator valve relieves at ~71 psi and the control valve relieves at~156psi,so if you have no eccentric by-pass valve you should have at least 71psi when you start up cold.If not the oil pump is weak,or an obstruction or leakage in the system.
My experience with oil coolers exactly matches that of Hailers.
Just as a matter of interest what grade oil do you run? I run 20W50,5W30 and 10W30 always result in lower oil pressure.
To Scott:if you read the owners manual for your car it describes oil pressure behaviour on cold start and warm up.

 

If I had known it was done by Atkins I would'nt have mentioned the cover gasket. Hard to believe a reputable outfit like that would have screwed up. Shoulda mentioned the eccentric shaft bypass but I see that you have that covered by the rebuild. The mans right, call Atkins. I'd still make a effort to install a aftermarket oil gauge to see what you really have. You'll note in the fsm when they check the oil pressure, they do not use the gauge on the auto. They install a manual pressure gauge. Says something, them doing that.Edit: oops i see, you said autometer gauge on the adapter.

 

I am having a hard time finding a mechanical oil pressure gauge like mentioned in the FSM. I remember seeing one in the JC whitney catalog for $20 but i threw it away

James