Oil Pump Or Bearing Failure - Is This A Valid Way To Diagnose?
 

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 diagnosis?

Thank you

Not sure about that one....


Have they not put a mechnical gauge on the car and tested to see if the it's the sending unit?

Beyond that- I'd inspect the pressure relief valve, then finally the pump. Didn't think there was much to a pump beyond some hardend gears.


Michael

It does not sound to me like a reliable diagnostic process. Did this happen suddenly or over time?

First, replace the sending unit and the 2 "o" rings on the filter shaft. Its on the oil filter housing and takes all of 10 minutes, a 13 mm wrench and a $30 part. Then you will know if there is a problem. Don't readily assume that it's worst case.

It's a 350.

SO?

Sudden drop in pressure. Oil filter stem O rings have been replaced and low pressure verified. MB dealer tells me there are baffles that sometimes fall into the pan that cause oil pump pick up obstruction and these oil pumps sometimes shake their mounting bolts loose. The dealer is dropping the pan this week to have a look.

Can you use just any "o" rings on the filter shaft? I've noticed that mine are rock hard but I still have excellent oil pressure.

lietuviai,

I suggest you go to your local MB dealer NOW and get the two "O" rings for less than $5. They are probably $.25 ea or less elsewhere if you can find the right size, is it worth it? Maybe they are treated to withstand the constant oil bath and heat, who knows?

Thanks for the suggestion. I guess the "NOW" emphasizes the urgency of the matter. I thought since my oil pressure was good, it didn't matter. I hope this doesn't make me sound like a neglectful idiot.

lietuviai,

Not at all an idiot. We are all trying to help each other here.