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

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

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

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

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.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

It's a 350.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

SO?

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N. Hodges
1994 S350
1987 300 SDL (for sale)

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.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

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.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

lietuviai,

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