Rotate the temp dial back and forth a tiny bit when it acts up -- the 300TE has a tendency to stick on hot or cold, and I have to wriggle the dial to get a decent temp. I've heard this is loose pins on the circuit board, but I've not dived in yet to fix or find another one.
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!