BAd gauge or sending unit will do it every time. So will a bad visco clutch or a bad pressure cap. The latter will make it "burp" coolant after a highway run.

visco clutch must cause the fan to draw large amounts of air and roar for a second or so on startup until the fluid spins out of the working zone, and draw large amounts of air and roar when hot. Must stop within a single rotation of the engine when shut off hot, any more than that, it's toast.

Less fun are dragging brakes, slipping tranny, blown head gasket.

If it runs hot in slow traffic, but stays at 85C on the highway, replace the visco clutch.

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!