For the switch in the head you can also adjust the turn on temp by placing a resistor in parralel. Can't remember the exact value but different ones make the temp different. I adjusted the one on my 103 to kick on at 95 and got away with a bad fan clutch for several years (was poor college student).

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1990 300e 230k (old reliable) sold
1987 300D 230K sold
1987 300D 232K 5 speed
1998 E300 140K