Normal engine temp is 85, plus or minus 5, higher under load and lower
if outside is very cold. The aux fans kick in between 100 and 110,
depending on year/model and engine, or when A/C is running.
In older MB (80s), aux fans can run in normal speed (A/C running) or
high speed (engine hot). I am not sure about your model.
RE: AC and Aux fans
Not sure about this model, but in many older MB's, eg 116, the aux fan
does not automatically come on with the AC. The temp at the
receiver/dryer has to be above a certain temp, which is pretty hot, so
it only comes on if it's a very hot day.
On my W201 and W126, the A/C pressure turns on the aux fan. Unless the
refrigrant is very low, the aux fan is on within a minute after
compressor runs. I have another W202 but I am not sure how it runs.
All late models have many computers on board, so the on/off probably no
longer depends on a single temp/pressure switch.
This discussion gave me an idea. I have a 116 that was converted to
R134 some years ago. With the conversion, you lose some cooling
capacity, maybe 20%%. So, I'm thinking if I bypass the temp switch
on the receiver/dryer, the aux fan will always go on with the AC.
That should help lower the outgoing refrigerant and provide some
additional cooling capacity on days when it's not quite hot enough for
the fan to go on via the temp switch.
AT any rate, I don't see any downside.
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