Do not drive it without the thermostat in place, it will seriously overheat. MB coolant systems require that the bypass orifice be closed by the plate on the rear of the thermostat to force water through the radiator. Without the orifice closed, the coolant will cycle around the block and head (and heater core) only.

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!