Ok, new to here and i have been reading other posts and nobody seems to have the same symptoms i have been getting. Recently purchased a 2000 ssei 85k, second owner. Car was kept up with, have the records. Two days and one trip after purchase, the oil pressure dropped while driving and flucuated between 0-40psi depending on foot on pedal. I replaced the obvious pressure sensor, as there were no signs of bearing wear(sparkles in oil). Still no change. I have had a shop tear down the pan and adapter to check passages. No signs of rod cap play or main bearing wear. So everyone is saying oil pump. But with the VERY low failure rate on the pump on these motors, i am very skeptical. This is the 5th 3800 i have owned, so i am not new to these cars and motors. So, there is a low end knock at startup and only lasts for a few seconds while pressure builds, gauge pegs at 120psi, and car will drive just fine until the oil warms and thins and then the pressure issue becomes apparent again. There is no other knock through the rpm range. Car has been driven very little since this started as to prevent any further damage, only started ran for a min or two and back off. So if ANYBODY has any thoughts......please share. Thanks!

alot of times when the sensors go they leak a bunch of oil into the plug area, i would check that over with a fine tooth comb first, it doesnt sound like any thing mechanical

Thanks, i replaced the sensor. I also pulled the plugs, there was a small amount of white on the tip, from oil not circulating. The old pressure sensor looked crappy, tarnished and oil in the plug. Now its shiny and new, cleaned the pigtail as well. The knock i get at startup and warm up, sounds like rod knock. Except when you give it gas, it dissapears. Most rod knock coinsides with rpm ie.. slower faster. Thats whats throwing me off. Cant figure it out.

if you cleaned the sensor plug already could be right readings. did they change the oil and with what? you said it goes to 0 after it warms up at idle? does it knock when the gauge shows 0?

I think you've been duped.

Are there any records indicating lower intake gasket work? This job would be in the several hundreds of $ if it was done at a shop.

If you have no records, then I think it would be safe to say the original owner never had the gaskets done. I guess it doesn't matter either way. If they were done, then the damage is already taken effect. If not, the damage is ongoing at the moment.

At any rate, your in the market for a new engine. Nope, heavier oil won't change anything. Its now a matter of when, not if.

This is a common problem with just about any V series GM engine. Lower gasket fails, it allows coolant to get into the oil, the mix turns acidic and eats the lower bearings.

I would want to remove the oil pressure sensor/sender & get a real pressure gauge screwed in to actually see where the oil pressure is really at first.
What is the idle rpm?

There is a spring loaded oil pressure relief valve in the housing the oil filter attaches to, located right above the oil filter. Sometimes it gets gummed up and sticks open, resulting in low oil pressure. Very easy fix to take it out and clean things up so the relief valve moves freely. This is a fairly common failure on the 3800 and could very well be your problem.

Here is an old write up that explains how to get at the oil pressure relief valve:

https://www.gmforum.com/general-gm-c...re-mod-295611/

Fairly common problem? Where?

That'* the direction I would also head. Right behind the oil filter adapter housing.