1991 350SDL diesel has ok oil pressure when first starting cold. After about two to three minutes it drops at idle to close to zero on the gauge and will go to just beyond "2" on the gauge at 2000 RPM.

MB dealer here says to determine if it is oil pump or bearing failure they would dump the oil thats in it and refill with 20-50W, then if pressure holds steady it would be a bearing failure if it drops as it is doing now they would say it is an oil pump failure. Does this sound like an accurate way to make this judgement?

Thank you.

Chances are, its the oil pump failure. Replace it RIGHT AWAY unless you want to throw the car away. I had the same issue, low oil pressure at idle, and lower in the summer heat and it was the oil pump. I didn't replace it in time and it lead to bearing failure and the motor got junked. Started to knock and then it was toast and on its way to the junk yard.

Do not drive the car any more until you decide what you want to do with the car. Good luck and let us know what it ended up to be once you know for sure.

-=>Raja.

__________________
1983 MB 190E, bought from Germany and shipped to the US in 1986.

I'm hoping it's the pump as I really want to keep this car. I'm original owner and it's in awsemome shape otherwise.

Just remember the golden rule: Oil is the blood of the car and a faulty pump is a heart attack. Treat it like "code blue" otherwise your car will die. Well, not so dramatic but its essential that you don't drive the car with low oil pressure. Knowing what I know now due to my previous experience with this issue, I would have the car towed to the service place rather than drive it there.

Good luck with it and I'm sure you'll get it sorted out!

-=>Raja.

__________________
1983 MB 190E, bought from Germany and shipped to the US in 1986.