My wife came home in the E300D and I noticed that the left (driver's side) electric aux fan was running, although the engine was not that warm -- between 80C and 90C, maybe. It got me wondering, what triggers these two fans? a/c line pressure? coolant temp? moon phase?

I know that the OM603 engine in the W124 car has a single two-speed fan that is switched on in low speed by the a/c and high speed by the coolant temp (did I get that right?) but the '96 E300D is the first car I've had that has two electric fans in addition to the mechanical fan with clutch.

I did some searching . . . there are four pages of threads for "aux fan" and one for "auxiliary fan" but few posters bother to say which car/engine they were writing about and I didn't feel like reading each one.

I ask this strictly out of curiosity -- I am not, nor have I ever been, a member of the Overheating Party of the USA.

Edit: It appears that the right (passenger side) fan is driven from the left fan by a belt . . . and my belt is missing, hence only one fan works. I'd still like to know what circumstances cause the fans to work, though.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970