MattyRoose

Hey all. Wanted to pick your brains.

Randomly at start up, I have the oil pressure idiot light on and my oil pressure gauge reading zero. Was fine when parked last.

Happened about 500 miles after belt/water pump change. Happened IMMEDIATELY after I drained the radiator as part of coolant flush. (The last part should be unrelated.) Car was parked on 4" ramps for the week prior. Car runs just about every weekend.

What I have done with no positive results:

1. Cleaned contacts for oil pressure sending unit.
2. Replaced oil pressure sending unit.
3. Primed oil pump though the oil filter hole.
4. Re-torqued crank bolt to spec.
5. Changed oil and filter, filled to spec.

I actually think it HAS oil pressure as the engine idles smooth, but I don't want to run it for an extended time if it doesn't actually have pressure.

I have NO voltage at the ends of the wires at the oil pressure sending unit, not sure if that's normal.

Wires to the sending unit are sad looking. Was thinking of new wires at least up to where the sending unit ones meet the larger wire tube at the front of the motor to see what that does.

Any other ideas?

1983 944

Thanks!

968workaholic

Put a mechanical oil pressure gauge on and see what the actual pressure is and go from there. Could just be a wiring harness issue between the gauge and sender

Van

I bet the 3-piece OPRV (oil pressure relieve valve) is stuck open. It's kind of near the oil pressure sending unit and is comprised of a cap, a spring and a plunger.

Thanks that all apart, make sure everything's clean and there's no scoring on the plunger, and then put it back together.

mytrplseven

If oil pressure was zero, your lifters should be clattering like crazy. You wouldn't be the first guy to replace the oil pressure sensor only to have it be bad. What brand did you buy?

jspearin

Usually when the oil pressure senders go bad they indicate max pressure on the gauge, not no pressure. Check to make sure you don't have the leads reversed on the oil pressure sending unit.

harveyf

When you take off the oil filter, is it full of oil? It should be. Even if the OPRV is sticking open, that is downstream of the filter. Of course, if the gauge is wonky, the filter should be charged with oil.

It's counter intuitive, but the center post hole on the oil filter does not lead to the pump, that is the outlet. You want to prime by pouring oil into the oblong opening out on the perimeter of the fixture.

MattyRoose

Thanks for the ideas!

1. I bought the $70 sending unit, not the crap $25 one but not the $125 VDO.
2. Oil filter had some oil in it but not a ton - but I also changed it cold when it had been sitting for a week or so.
3. I primed the center hole not the other one. Doh! Easy enough to re-prime the right way I guess.
4. Cleaning oil pressure relief valve seems pretty easy to do. Do I need the alignment tool?
5. I was thinking about putting a mechanical gauge on it to see, I guess I can swallow the $150 it would cost to get the Lindsay Racing adapter and a mechanical gauge set up.
6. No noise from the lifters. Engine sounds normal to me, but the risk of not having oil pressure and letting it run scares the poop out of me.
7. The new OPSU had different posts than the previous, but old sensor had worked fine wired that way. The new one has two different sized posts - both with tabs to plug into. The old one had one tab, and one connector that was held by a nut directly on the post. I guess I could switch the wires and see what happens.

harveyf

It will make a hell of a mess but if you leave the oil filter off, pull the fuse to the fuel pump, and crank the engine you'll know in about 3 seconds whether you're pumping oil. Even so, as Van says, you may be dumping it back into the crankcase if the OPRV is stuck open.

MattyRoose

So I FINALLY got around to looking into this.

1. So the oil pressure is NOT zero. Gauge sits about 1.

2. Take a look at this plunger, please? Is that sufficient scoring to cause an issue? It definitely popped out under pressure.

Thanks gang.

MR

MattyRoose

FURTHER update:

Cleaned and polished the plunger for the original not updated OPRV. Replaced. Still 1 bar of pressure.

Took off oil filter. Next to no oil in it, but oil dripped out of the oil filter base. Primed oil pump properly (didn't take much).

I am thinking now I have legit low pressure. I am going to put together a mechanical gauge to verify.

Whats the the next step after we confirm low oil pressure? Start with the $500 OPRV or go straight for the $800 oil pump.

willrobinson

Member V2 on here had an updated early block OPRV for sale in a post a while ago. A lot less than $500

autocomman

After going into my 951 for a reseal (it has good oil pressure) I question how often the pump actually fails VS the anerobic sealer failing and the oil pump pick up seal going bad. The pump is literally glued to the block, if the sealer fails whose to say it working properly..then again its so much work to get to it why would you chance the original pump

mikehayes

I have never heard of one of these oil pumps going bad. Especially just out of the blue like that. If you could figure out what the closed position of the oprv was, you might be able to put a spacer inside the spring to keep the plunger from opening and install it to verify that it is actually what's causing the problem.

Van

I've seen crank bolts back out... which will cause the oil pump drive gear to slip.

But, it's much more likely to have a cracked oil pickup tube... Any chance this engine has been run either without the balance shaft belt and/or with the balance shafts out of time?

MattyRoose

Van - I thought the exact same thing at first - but torqued to spec didn't fix it.

Not run run without balance shafts or balance shafts out of time for the 12 years we owned it.

Its currently on ramps providing a 6" lift. Would that impact anything? I can't imagine it would.

Cracked oil pick up tube. I'll do some research.