Description by vendor, car pins needle at three bar cold idle but sags to 0 bar once warmed up at idle. Resumes apparent normal pressure at cruise he states but his normal may be sub standard as he does not state what that pressure is.. He's saying it's the sender but I do not think so. States car has 122k but pretty safe to assume has under 200k I think. Car is too good in general to have much more as seats look like brand new. Spring must be coming as I am getting the urge to go buy another car. Wife will shoot me but whats one more wound. Maybe just the o rings in filter,or relief valve stuck partially open? Perhaps obstruction in tube. Oh yes car is 85 300d. Could of course be something more serious and do not think can get a chance to check it out prior to taking car. Know it could be bearings but thought it would be knocking pretty bad with 0 indicated at idle. Suspect he has already checked sender out as a problem as it does not seem smart to sell a car with this problem if it can be rectified so easily. Keeps the price down for starters. Any ideals?

Well Barry, I guess nobody wants to see you get shot by your wife, so I'll pass too!

I think you've covered most of the obvious and are hoping for another possibility overlooked. There may be one, but I wouldn't buy it before I knew for sure!

Hopfully someone here can spare your life, or jeopardize it with an answer!

When was last oil change-any chance oil is fuel diluted? wrong type/broken down? An oil analysis may be in order, I DEFINITELY wouldn't drive it without an oil and filter change(at least).

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K

All of the diesel W123's that I have worked on had mechanical oil pressure gauges. Which means that they don't have a traditional electric "sender."
I would suggest connecting a direct-reading pressure gauge at the oil filter housing.

Good thought bullwinkle, never occured to me in this day and age. But possible. He also states that he has been driving it in present condition for quite awhile in fact ever since he first purchased it. Could already have slight bearing or other damage.

a thread similar to this just resurfaced the other day. check and clear the pinholes at the top and bottom of the oil canister cap shaft.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Pull the dip stick and see if the oil is like water..
might be worth a change to decent oil (if the oil that is in there is old/too thin)

Change the oil, filter and o rings before you buy the car. See if that makes a difference.

Insist on an OE filter and at least a 15w-40 dino oil.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

FWIW, the minimum acceptable oil pressure at idle is only 0.3 bar. (Per the 617.95 service manual.)