Does the electric fan run when the engine gets into the upper heat range?
Pull over, open the hood and look if it's running.
If not, why not.
It has a temperature sensor, a fuse, a relay and fan motor; any of these
could be defective.
But if the fan is running and the engine is hot then the radiator may
need to be cleaned, inside and outside. This will be especially so if
the engine runs hot while at speed, not just in slow traffic.
I just had this exact same problem with my '94 E320. The fuses for both of
the auxiliary (electrical) fans had blown, a 30A and a 15A. (spade type, not
the usual pointy cylinder type) When they started up again for the first
time, there was a great cloud of dead bugs and bug parts flying out of the
radiator. I am assuming that this surfeit of dead bugs was the reason both
fuses blew in the first place.
Another symptom I had was that my AC, although it worked fine while driving
down the road (good air flow) would stop cooling as I slowed down for a
Hose out the bugs (not too much water pressure, it will bend your radiator
vanes), make sure that the fans turn freely, and check the fuses.
'94 E320 runnin' cool
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