My 350SD began heating up more than usual today and I got a little worried. When I got home from an 85 mile ride where the water temperature got over 100C a few times, and then cooled down when I was either running at 65-70 mph on level ground or down a hill, I popped the hood and found only one auxiliary electric fan in front of the radiator, oil cooler and A/C heat exchangers running. It was the passenger side one. So I have spent a few hours looking for clues in the forum here, and did a search on auxiliary fans. I could not make good sense of what I found, and have some questions if someone can answer them.

First, is the auxiliary fan fuse in the fuse box, position number 1, for these two fans? Are there any other fuses or relays that control these fans?

Second, is the fact that one was running and the other not, with the water temperature around 90C, an indication that the stopped unit is damaged, or are they controlled separately?

If they are controlled separately, where are the fuses or relays located and what might they be marked? I could not find anything under the hood that was associated with these fans other than the guide under the fuse box cover identifying fuse position number one as the auxiliary fan (not fans) fuse.

I will be trouble shooting the car in the morning and if I get any more clues or observations to share I will do so. Thanks, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I can't remember which position the fuse is in but both fans should run at the same time. They do run at two different speeds. Low speed when the A/C is having trouble cooling and the high speed when the engine is over heating. I beleive the high speed kicks in at 105-110.

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1991 350 SDL
183,000 miles

1982 240D
130,000 miles