[Jables17]

So I did an oil change on my 91 5sfe, drove the car a couple of miles and my low oil pressure light came on. I immediately took it back home, checked fluid levels, replaced the sensor, and the light was still on. I've read it is possible but rare for the pump to lose its prime after an oil change but also rare for an oil pump to fail. What is the best way to prime the pump and see if it will regain pressure?

I've already checked the pressure with a mechanical gauge and am getting 0psi when the car is running. Now I know for sure to refrain from starting this car until it is fixed.

Are there any other possibilities? I've checked the bypass valve in the oil filter, but I have yet to drop the oil pan and look around in there, although, I'm not entirely sure what I'm looking for.

Any help is much appreciated!

 

[J.harris]

An oil change wont cause this problem. I would look at your oil filter.

You can take your plugs out and crank the engine to check that you have oil pressure. If everything is normal your dash oil pressure light should go out after a second or two of cranking.

If the oil filter isnt the problem pulling the pan would be your next step. No telling what you will find. Maybe a loose pickup tube or clogged strainer. Either way hopefully your bearings are okay.

 

[Jables17]

I've done a little more research on the forums and found some things to check out.

First I'll do as you said, pull the plugs and check for pressure, although I doubt that will change things as I've already checked the pressure with the engine running. Course I won't be legitimately running it now that I know there is no oil up top.

Before dropping the pan, I've found a few people have fixed this issue by using a suction gun to suck up oil and then send it directly into the pressure sender port to regain pressure. According to the thread, this might help if there is air trapped in the pickup tube or elsewhere.

Pulling the pan will be the last resort for me, but if it comes to that I will check the strainer, pickup tube, and relief valve.

Is there also a relief valve where the filter mounts that can get stuck? Not talking about the bypass valve inside the filter.

 

[benckj]

Relief valve is part of the oil pump housing. Never heard about loosing prime after changing oil before.
I know this is a stupid question but are you sure oil is at correct level? Reason I ask is I had a friend who recently changed oil in his 86 and accidently left the old O ring attached to filter flange. Once it heated up the rubber gave way and he dropped most of his oil on road.

 

[luke]

You mention that you have checked the pressure... have you put a pressure gauge to the sender port to do this?

My first thought would also be to verify the oil filter is not the issue. This is an easy (and cheap) item to check.

You certainly should be operating under the assumption that you don't have oil pressure if the light is on (and certainly if you have verified via a gauge that there is no pressure at the top end). But, if you are only relying on swapping oil pressure sensors or some other reasoning for not having pressure, I would also verify that the oil pressure sensor's wire has not just grounded out. This would trip the light for good too.

Good Luck!

Luke

 

[Jables17]

Yes, fluid is full on the dipstick. 4.2 quarts filled just like the owner's manual specifies. And yes I checked it with a pressure gauge hooked up to the pressure sender port on the top end. It ran fine, but I did hear a slight ticking noise which I would assume is because of the lack of oil in the upper end. I also didn't swap oil pressure sensors, I bought a new one. But I agree, now that I've seen the new sensor with the light on and the pressure gauge still reading 0, I won't be starting the car again. I took my chances by running it for a few seconds to check these but now that I know for sure I have a major problem, the engine will stay off until I find the culprit.

Oh, I already checked the oil filter, it is a new filter, oil has run through the filter itself and the bypass valve is closed as it should be. But the presence of oil would mean it had pressure to send it through the filter during my short drive down the road before the light came on. Air bubble somewhere or stuck valve is my best guess.

To your point, I was actually hoping it was the wiring to the sensor, but the pressure gauge hooked up to the same port ruled out anything related to the sensor and wiring.

Sadly I probably won't know anything til the weekend but figured I'd look for thoughts and opinions here before then. I'm surprised it read 0psi though.. I would think I would see some amount of pressure between 1-5psi.

 

[J.harris]

It doesnt take much pressure to turn off the low oil pressure light in the dash usually below 10psi.