You have a defective visco clutch -- engine shouldn't be getting much above 85C in traffic unless it's REALLY hot.

You also have a defective pressure relief valve in the oil filter housing -- I've heard of this before. You MUST have 3 bar oil pressure by 1500 rpm or you risk bearing damage (read $$$$$$). The seat for the relief valve is bad, and won't hold proper pressure with the oil hot.

Normal oil pressure is about 1 bar at idle hot, maybe as low as 0.5 bar, rising immediately as the engine speeds up. On turbodiesels, it must not drop below 2 bar idleing hot (this is the opening pressure for the piston spray jets).

Before getting hysterical, though, you need to get a mechanical gauge on there and verify that the oil pressure gauge is correct! If so, replace the oil filter housing (relief valve is not available separately) and see what happens. Cheaper than a new engine!

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!