The fan does come on at 100C. I don't have a coolant tank on the top of the wheel well, I just have a cap on the rad. I just replaced the rad cap with a new one last week.

The fan clutch is engaged, it has resistance when hot and when cold. It stops spinning as soon as the motor stops running, it doesn't continue to spin.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg