Replace the pressure cap, too!

Check for a soft lower radiator hose -- if it's mushy, it can collapse at high engine speed, reducing cooling capacity. This usually only happens with a non-pressurized cooling system (bad pressure cap).

If you also get some coolant spill or brief boiling noise when you shut off hot, for sure it's a bad pressure cap.

Otherwise, it's time to check for coolant flow (difficult on this car) -- you may need to use an infared thermometer to check radiator temperature, it may be plugged from residual crud from the cooling system (bummer!).

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!