95 3100 low oil pressure light

[seanzyyy]

I have just finished replacing the transmission, and doing the lower intake manifold gaskets in my 95 monte 3100. Upon starting the engine again for the first time after doing the manifold gaskets I end up getting an oil pressure light after 30-60 seconds after starting up the engine. I did change the o ring seal for the oil pump drive when I did the LIM, but I can't imagine that I did anything wrong there, it was fairly straight forward remove the shaft and change the oring, I was sure the oring was in the exact same groove it came out of. Reinstalling it I simply dropped it in the hole, moved it a little until it fully dropped in and worked the oring down, installed the hold down and bolt.

Other things I noticed or you might want to know:

The engine doesn't sound like its running without oil. Its noisy, but its always been noisy for as long as I can remember having the car, and long before I did this work to it.

I did use 10-30 oil instead of 5-30, Its all I had handy when I was ready to fire up the engine and I planned on doing a filter and another oil change after the engine had been running for 15 minutes or so. Could something like that cause the low oil press light?

It doesn't happen right when I start the engine, usually doesn't come on for 30-60 seconds after. It slows fades on, and doesn't dissapear when I rev the engine

Peering into the oil fill cap hole I can see the bottom part of the heads filling with oil it looks like.

Oil and coolant levels are normal, doesn't appear that coolant or anything is getting into the oil.

I did pressure wash the engine while it was out and quite possibly nailed the oil pressure sending unit with the sprayer.

I did NOT do the LIM because they were leaking, they were not, and I never had a situation that coolant go into the oil while the engine was running. I only did it because the engine was out and I'm sure glad I did as they were indeed factory plastic ones with over 100k miles on them and starting to break down.

So after hearing all this what are your suggestions? Could this be something as stupid as using 10w30 instead of 5w30? Is it possible to connect an actual oil pressure gauge to the engine to see what its actually at, if so, anyone know the size of the fitting off hand? Could I have screwed something up when installing the oil pump drive? Is it really possible to screw that up?

[geoffinbc]

In the block there is a 1/16" NPT pressure port on the block right near the filter mounting pad. If there is a filter adapter on your car there is sometimes a port on the adapter. You can check for pressure on these ports.

There is no reason you cannot use 10W30

I am guessing you car does not have a gauge so an actual pressure check is crucial before you drive the car. If you hear any clicking noises then shut the engine off as that is a sign the lifters are low on oil.

[robertisaar]

In the block there is a 1/16" NPT pressure port on the block right near the filter mounting pad. If there is a filter adapter on your car there is sometimes a port on the adapter. You can check for pressure on these ports.

There is no reason you cannot use 10W30

I am guessing you car does not have a gauge so an actual pressure check is crucial before you drive the car. If you hear any clicking noises then shut the engine off as that is a sign the lifters are low on oil.

hell i run 10w40 when i can find it (provided its not winter). and no the 95 montes didn't have oil pressure guages in the cluster(3100 or 3.4)

[seanzyyy]

Went out this morning to continue working on the car, started it up, and it ran without the oil light for a good 1-2 minutes before it slowly faded on and wouldn't go away again. I am heading to town to get a manual oil pressure gauge to see whats actually going on here.

In regards to where I can connect the oil gauge, I see a bolt kinda between the oil filter and oil pressure sending unit, off tword the starter, is this the location to tap a pressure gauge? I would assume for temporary checking I can just hook into where the oil pressure sending unit goes into the block and replace the unit when I'm done testing?

[robertisaar]

i think the PCM is designed to kill the motor if it doesn't see a certain amount of pressure(dont quote me on that though), so i'm not sure if that could be an issue. and it just slowly lights up? is there a possibility of the guage cluster going bad? my wifes 90gp does that sometimes with the check guages light and its all kind of FUBAR; shows the RPMs 2.66 times what they really are, speedo is tripled, low fuel light wont go off, check guages is almost always on. do you have any of that kind of stuff coming up?

[bszopi]

I would think it would be a sensor issue before a dash issue. OPSU are cheap enough, it might be worth it to just replace it and go from there. Especially since you think you might have washed it down.

[seanzyyy]

Nope not having any other issues at the dash, it was only the oil pressure warning light.

I noticed how cheap the sending unit was when I was going to buy a gauge so I figured screw it, I would skip the gauge and just replace the unit first to give it a shot. I also changed oil filter and oil to mobile 1 5-30, what I usually ran in the car before the tranny died. Started it up and no oil pressure light anymore, seemed to have either been the sending unit or the oil filter, guessing it was the unit though. Either way engine is running great now, thanks for the help!