Check the injection timing, and look for a bottom radiator hose collapsing under high flow conditions -- this restricts flow at speed and load, causing overheating.

Double check the thermostat installation -- I know it is a pain in the butt, and it something is restricting the valve opening, it may work fine and still not open all the way.

Do you have any pressure in the cooling system with a cold engine? If so, you have a cracked head or leaking head gasket.

Other than that, all I can think of is a flow restriction somewhere, and I can't think of a quick way to check that -- no cap on the rad.

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!