Hi, today my car dropped the oil pressure down to 0 at idle. But as soon as I gave it some gas it would go back up very fast. It's an 84 300SD. What could cause this so sudden? It was fine yesterday.
Stuck oil pressure relief valve?
The oil is kinda old (4500 miles) and so I changed it and now it idles at 0.5 bar which is fine according to the owners manual, but I do think that there is something very wrong, considering it was always at 1.5 bar before, even in very hot weather and the temp gauge at 90. The car has 391K miles on it.

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1984 300SD, 384K miles. Gold/brown.

Replace your oil filter -- there is an internal seal that can get displaced allowing the oil to run back through the bybass filter into the oil pan. Causes instant low oil pressure.

It's also possible your idle is low -- you should have 2 bar pressure all the time, as that is the closing pressur for the oil jets.

At that milage, could also be a bad oil pump.

Can also be a bad pressure relief valve leaking at low oil flow. You will need to replace the oil filter housing to fix that, it's buried in there somewhere.

Do you get full oil pressure above 1500 rpm? If so, I'd also have the pressure checked with a known good mechanical gauge -- oil pressure gauges have been known to fail, after all!

Worst case it's engine rebuild time, although I'd be surprised if the low pressure showed up suddenly like that.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!