For those finding this post in searching for solutions to the
overheating, aux fan problems for the 300E W124, I thought I'd add my
1988 300E at 260K miles was overheating etc. Had a shop (Ditmire --
recommended!) put in a 100K M103 engine with new head gasket etc plus
new waterpump, radiator etc etc.
After all that, still had an overheat problem and realized the aux fan
(older W124 single fan system) was bad -- binding and blowing fuses.
Finally replace that. I also add in Forgione's resistor mod to kick
the fan in earlier.
First hot day in 2007 I think I'm all ready. 85 degrees, aux fan kicks
in when it should but the temperature continues to proceed up to 120 C
and the redline. Cursing, I am!
Turns out the new aux fan was spinning counter clockwise. The
connector goes in one way, so I think the fan was wired backwards when
it was manufactured. I reverse the wires and the car is finally now
maintaining a nice temp
And a thanks to all those who posted information here over the years
that was all very helpful. This is my contribution to the pile.