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.