Hpjc10

hey all, i have a 1987 z31 NA, and its having some worrying oil pressure issues. the ODO says 349k miles, I rebuilt the heads because of a couple bent valves, put everything back together with new gaskets etc, and for the first 2k miles it was fine. I then went to NTB to get my oil changed, used some high milage oil and about 3K miles after that my oil was black, and my oil pressure gauge never reads above 15 psi now, even before the rebuild, the guage never passed 30 (i know its supposed to be between 30-60psi....)

anyway, the problem im having is that my passenger side head is not getting oil, the lifters tap and i add a bit of oil and it stops. more recently my oil pressure has been reading close to or at 0, and goes up a little bit at highway speeds, except for when i am cruising or decelerating.

im thinking it could be one or more of a few things. i dont think its the pump because my drivers side head is getting oil. maybe the pickup screen or one of the main galleries is clogged? I also think maybe my sending unit isnt accurate as it never read higher than 30 psi and didnt change with speed.

any ideas would be great. i was thinking of pouring some seafoam in the engine and then just driving it a bit then changing the oil again. i really dont want to drop the pan or take the heads off again....

ken99

At 394K, yes, it could be an oil pump issue, most likely a sticking pressure regulator plunger or a bad seal. Test the oil pressure by unscrewing the oil pressure sending unit and plumbing in a mechanical gauge. Minimum pressure values at specific engine RPM are published in the FSM.

Hpjc10

So i put the seafoam in the motor oil and drove for about 100 miles, per recommendation on the website. I have to note, the dipstick read full.

So i went to change my oil (5w30 castrol high mileage and a fram extra guard filter) i ran my car for 15 mins or so, then drove it into the garage, and drained the oil. Only about 2 quarts of oil came out... It was black as tar and really thick. I let it drain by jacking up the drivers side ( to angle the drain down) and let it drain for about a half hour. At that point i changed the filter and put everything back together. With the new oil, i started the engine and the pressures was back to where it was reading before the problem, a bit more than halfway between 0-30psi. I didnt drive it but it looked like it was holding steady at idle.

Someone told me that the old oil might still be in the engine behind a clog somewhere.... I had changed the oil ~2500 miles ago on 9/14, so either my engine is burning/losing a lot of oil or theres a really bad blockage somewhere. Either way, i think this engine might be on its last leg.....

What do you all think?

Hpjc10

So another quick update, drove to work this morning, and at first (while the car was cold) my oil gauge read ~30 psi at ~35 mph. Once it was warmed up, the gauge dropped again. Heres a video of me on the highway this morning. This is what its been doing before the oil change thats been bugging me.


Any ideas?

ol55

Any ideas?[/QUOTE]

I'm no pro -but you asked. See if you can find a mechanical gauge to confirm the low oil pressure. ( I don't have sound with google chrome so I did not hear your engine but seems like it would not run at all with zero pressure).
I used marvel mystery oil to quiet the lifters in an ot miata with some success (they have a "flush" procedure on the web site that is more aggressive than what I did). Seems like a solvent like mmo may be worth a try.
Would soaking /cleaning out the gauge help?
If the problem did not happen with regular vs high mileage oil, maybe switch to another regular oil.
Could you remove a valve cover and blow compressed air down the oil passage on the one bank to clean out an obstruction?
The filter you used has been questioned by other sites. I'm not picky on filters.

Only Ideas...

Hpjc10

so it turns out, the people i had change my oil (i usually do it myself but didn't have time, and it was actually cheaper than buying my own due to a deal) must have hit the oil pressure sending unit because its tank was able to rotate on the threaded portion and was leaking oil. it was sending funky readings because it was busted. I replaced it with a newer maxima one because the z 31 one was like 65$ and i would have to wait days, this was around $6. it has the same thread so it plugs the hole but the electrical connector is a little different and i dont feel like messing with it.

i changed my oil and the ticking stopped (except when starting the enginecold and has been sitting for a few days) and i dont have an oil pressure reading but i think its fine.