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Low Oil Pressure


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Well, I changed oil and the filter last Saturday, car ran fine, Saturday, Sunday and Monday morning to work. Last night I lost oil pressure when I first started the car, and it started knocking after a few minutes, so it is real. This happened to me about a year ago, per Bbobinski, he had recommended overfilling the crankcase with 8 quarts, to submerge the the gerotor oil pump, and "blow out" the pump relief valve. This worked a year ago, but it did not work last night.

The only thing I can think of doing now is possibly draining the crankcase, filling with kerosine and see if that will clear it. Other ideas would include pulling the oil pan and checking the sump screen, if I remember you cannot pull the pan without lossening the engine mounts and jacking the car up ('93 NS).

Any other ideas, short of R & R the oil pump, I think I remember someone saying getting to the pump requires pulling the engine.

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There is no way this failure mode can prevent priming if the oil level is above the level of the pump. So...if this doesn't work then there is another problem......

I added two more quarts of oil, so now I have added 10 quarts over and above the full line mark. I cranked it and it is still knocking (starved of oil), and I still have the low oil pressure warning. If you pull the dipstick, wipe it clean and check the oil level, it is over halfway up the dipstick. I know the last time I had this problem I added 8 quarts over and above the full line, and it solved the problem, so the pump relief valve must be submerged.

Is it possible the relief valve is permanently stuck wide open, and because of this, the oil pressure is minimal, even submerged?

Since I just changed the oil and filter this weekend I am going to replace the oil filter, although I feel it is remote it would have any impact.

Short of that, the only other possibility is the oil pump itself, I can't imagine it could be a sump screen, because I change the oil regularly. I also see no correlation between this issue and the phenolic spacer plate cleaning a week earlier.

Any more ideas?

Regards!

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Did you start it with the severe overfill. You will probably have to start the engine to get enough RPM to get the system to prime and shuttle the relief valve. Even if the relief valve is stuck open it will make oil pressure with the RPM up sufficiently. About the only reason it might not is if the oil pump drive is slipping on the crankshaft due to a loose damper bolt. Was there any work done on the engine that required removal/replacement of the damper/damper bolt. Even if the work was done some time ago, if the damper bolt was not tightened sufficiently/correctly or the damper was installed incorrectly it could cause an eventual loss of torque on the damper bolt and subsequent slippage of the oi pump drive sleeve on the crank snout.

The oil pump pressure control/relief valve on your pump is a small, spring loaded poppet valve. It is NOT a plunger style valve in a sleeve that can "stick" or jam like you may be supposing. The poppet style valve can trap some debris between the poppet valve and the seat which holds it open causing the loss of prime condition but it really doesn't fail or stick. Starting the engine will turn the oil pump (assuming the damper bolt issue isn't entering into this....) and the oil pump will pump and make pressure. At higher speeds then pump will make much more than the poppet can handle so the engine will have oil pressure. Start it and rev it up to 2500 or so. Even if it is making some noise it won't hurt it as long as it is in neutral and no load. With the overfill of oil the crank bearings are getting PLENTY of oil (they are submerged in oil) so there is little or no chance of hurting a rod or main bearing. The only noise will be the lifters starting to pump down and they won't be hurt by this.

If you want to do a quick oil pressure check unscrew the filter and bump the motor over....you should get oil out the filter port as it comes directly from the oil pump and will confirm that the oil pump is indeed pumping. If you take the filter off, bump the motor over and don't see oil delivery I would seriously look at the damper bolt....I guess I would look at it anyway at this point to make sure it is tight. Put about 300 ftlb on it to confirm that it is tight....that is about what it takes to reach final tension on the bolt on your engine.

Thanks for the info, I did not check the damper bolt, nor has it ever been removed, however, its definitely something to check.

I am alo going to loosen the filter and start her up tomorrow night.

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