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Re: <E30> M3 running hot

Anthony Wrote:

>>Can anyone tell me how to test my aux fan switches<<
>>and its wirings?  I want to make sure everything is<<
>>working OK before I core out or replace the ratiator. <<

With the car running, short the plug in terminals on the wires 
to the temperature switches mounted in the radiator together.  
One should start the fan low speed, the other high.  If they work 
properly you know the wiring and relays are OK. (Some later 
versions may utilize a single double-throw thermo-switch) Be 
careful, the fan isn't designed to go from a dead stop to high 
speed, if everything is working properly it starts in low speed, 
then changes to high when the temperature calls for it.  If the 
fan works then your problem is upstream in the power 
distribution system.

If the fan doesn't work then the poblem is downstream, relays, 
wiring or fan itself.  Keep in mind when you are diagnosing this 
stuff, that the relay contact sockets are "hot" all the time, if 
you jumper within the socket between where pin 87 and pin 30
of the relay plug in, the fan will run (usually relay K1 for normal 
speed, and relay K6 for high speed) even with the ignition off.  
However the sensing lines to the temp switches in the radiator 
itself are only "hot" with the engine actually running.    

On my 7-series I discovered a loose electrical plug near the two
temperature sensors in the passenger side of the radiator, a simple 
male/female blade connector, each on a single wire.  There also 
was a small round device in one line, I assume a diode. Once I 
reconnected this plug, the fan works fine with the AC on.
    
The water thermostat should open at 176 F and normal operating 
temp is about  190 F (about middle gauge)

Auxillary cooling  fan should activate at 196 F at low speed or 
ANYTIME the A/C is on.

High speed auxillary cooling fan should activate at 210 F.

Gauge red zone indicates temp is higher than 210 F.

The temp switches are fairly simple to check, especially if they
are mounted high in the radiator (mine are down low and require
a major drain, which is a major pain).  Remove the switches, grab
an old sauce pan, an ohm-meter and one of grandma's cooking 
thermometers.  Attached the ohm-meter leads (a continuity 
checker will work) to the switch contacts, drop the switch and the
thermometer into the pan with water and heat on the stove.  
When the water gets to the rated temperature, the ohm-meter 
should read zero or close to it.  You may have a hard time getting 
the water hot enough to activate the high temp switch, I couldn't 
get it above 210F, so I just suspended it over the gas flame for 
another fifteen seconds and it worked.
  
If the budget allows (about $12 ea at the dealer), just buy new ones and
check  
them a few times before you put them in.  There is a lot of variable
tolerance in 
these, and they fail often in the first couple of heat/cool cycles.  Besides,
checking new ones keeps the kids from whining about that ethelyn-glycol 
taste in their spaghetiO's!      :-)

HTH 
             \\\\I////                    Kevin Heiner
             ( o o )                     [email protected] 
- --oO0o------U------oO0o--         745i turbo