I was driving in a heavy downpour last Wednesday and when I came to stop
light I noticed an odd vibration in the steering wheel and under my feet.
It took me a few minutes to realize that the vibration was my radiator
cooling fan running on high speed.  Now that might be a regular occurrence
for some folks but doesn't happen very often here in the cool and damp
Pacific Northwest.  My temp gauge was reading normal, it was about 64
degrees outside and I was driving along in light traffic with very few
traffic lights.  Something was amiss.

My 85 Westy does not have A/C so the only time the radiator fan runs is on a
rare hot summer day in stop and go traffic or when I'm compelled to force it
ON with a jumper wire to sure it will still work when I need it.  (yeah, I
know it sounds nutty but it's become part of my routine before taking any
long trips where I might encounter different weather)  When it does come ON
it usually only come ON on low speed.

Any hoo, after I realized the odd vibrations were relatively harmless, I
continued driving with the radiator cooling fan running full tilt because I
didn't want to try to fix it in the pouring rain.  This was not the normal
heavy Northwest mist that we usually have, this was big drop heavy rain, a
1/2 inch of water on the roadway, cowering pedestrians on the sidewalk
getting splashed by passing cars, rain.  Ark building rain.

When I got back to my shop I removed the lower grill and unplugged the
connector to the temp switch that activates the radiator fan, and the fan
stopped.  The radiator was cool to the touch and the connector plug boot
does not appear to have been infiltrated by the rain water.  Simple answer:
bad radiator fan sensor/switch.

I stole the radiator fan switch from my other Westy (it's waiting for a head
reseal) and installed it in my 85 and now the fan does not run all the time.
I checked the old switch with my multi tester and sure enough, the sensor
switch is stuck ON and on both the low and high positions.  Weird.

Problem solved but I'm curious about this type of sensor failure.

I've replaced a few of these over the years for NOT turning the radiator fan
ON but never had one of these sensor/switches fail in the ON position.  Has
anyone else?  Do you think the heavy rain had anything to do with the
failure or is that just a coincidence?  I can't quite see the rain as a
factor but.it's a Vanagon!

Andrew

Bainbridge Island WA