RE: HELP e34 overheating

["Fadeev, Alex" <Alex.Fadeev@xxxxxxxxxxxxxx>]

> 1) If I let the car idle, the car will work itself into the red zone
> (temp gauge)..and the coolant light will come on on the dash.  The Aux
> Fan never kicks in (cept if I jump brown to black/yellow/grey).
> 
> 2) If I drive the car for miles on the interstate, same deal.  Needle
> works itself into/close to the red.

First of all, does your regular fan work? Can you stick a newspaper into the
path of the blades and stop the fan (with the engine hot)? If so, your fan
clutch may need to be replaced. 

Second, your auxiliary fan has a bad resistor - the dirty black rectangle in
front of the fan. It is held in place by tiny phillips screws. If you are
careful, you might be able to replace the resistor without stripping the
screws. Otherwise you might have to take the aux fan out (moderately time
consuming).

Third, when was the last time you replaced your coolant? Driving down the
interstate _should_ cool the engine even wit ha dead aux fan. But only if
the rest of your cooling system is well. When was the last time you had
water pump replaced? You might also trying bleeding air out of the cooling
system to eliminate that possibility.

> 3) I found one of the wires to the Radiator Temp Sensor had broken
> off.  reconnected the wire...didn't help with the overheating..fan
> never comes on (cept if I turn the air cond. on).
> 
> 4) If I jump brown to black/yellow/grey, fan runs fine

Replace the aux fan resistor.

> 5) When I do force the fan to operate (jump brown to
> black/yellow/grey), the needle still works itself into/close 
> to the red.

...so airflow is not the cause of your problems..

> 6) I went and bought a new sensor but haven't installed thinking it
> *might* not be the sensor so I'd wait to install it before I properly
> diagnosed the problem (saving $50).

Dealership may not take an electrical component back even in its original
sealed packaging. 

> How can I tell if this is a fan clutch or water pump?  Does it sound
> like there's two problems?  Sensor AND something else?

Aux fan resistor AND something else
 
> I was supposed to drive to Hoboken, NJ tomorrow, I'm getting a bit
> nervous that isn't going to happen.

David, if you are not happy about tearing apart your cooling system, take
the car to a reputable mechanic. Either way, I would not take the car on a
long trip before the problem is resolved.

Good luck,
alex

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