Jim:

Quality control on auto parts, even the German stuff (usually made in India these days) is going to hell. Bad thermostats out of the box are VERY common.

Only comment I would make is to replace the radiator cap, too -- I've had two bad ones now on 87 vintage cars, and have heard of several more at my local repair shop. Either won't hold pressure (the case on the 300TE -- fine until you stopped, and it blew coolant out) or won't vent vac, so the hoses are collapsed cold.

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!