Fwd: Radiator fan switch 2

[Huw Powell]

> Thanks for all of the suggestions from you all. I am having a problem
> with my 85 Audi 4000s quattro overheating.  I have replaced the
> thermostat at the engine and the thermoswitch at the radiator. I've
> cleaned the terminals at the thermoswitch. Wiggled the Relay, it is
> clean looking on the outside.  I've replaced the overflow reserve
> tank cap.  I've noticed that when I power on the car, either when its
> cold or hot, the idiot light for the temperature
> Gage/engine-temp-indicator  flashes while the other lights stay
> constant.

That's normal, that light has a flasher in circuit with it.

> While idling the car warms up as usual till it gets hot
> enough to set off the thermoswitch for the fan.  It will then cycle
> on and off for about 10 cycles, keeping the temperature in the normal
> range.  It seems that at some point the  temperature gets too hot in
> the engine or in the relay and the cycling stops and  the engine
> overheats and boils over.

Sounds like the relay is giving up the ghost.  Considering it is a 
simple SPST relay, swapping in another should be your next step.   Heck, 
there ought to be an AC relay or something in your fusebox you can steal 
temporarily just to test it out.

Now, it is possible that the relay is stopping because something else is 
hurting it, like a rad fan that draws too much current, but swapping in 
another relay is a good place to start.

>  If I stop the car and turn it off, while
> the car is still very hot, the fan does not continue to work to cool
> the hot engine as it does on other cars. 

That is run by a separate sender (on a bracket on the back of the head, 
basically) and, I think, a separate relay.  Things have to be pretty 
darn hot under the hood for that one to run.  All it does is get the hot 
air out from under hood, though, since the coolant is not being pumped.

> I've been told that the
> radiator may be clogged, but it looks clean, both hoses are hot and
> when driving the car at speed the coolant temp goes way down,
> indicating that the radiator is cooling albeit to well.

Unless it is very hot out, the coolant gauge should run at about 1/3 on 
the highway.  About 2/3 is where the fan kicks in.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/