Radiator fan switch 2

Steve Sears steve.sears at soil-mat.on.ca
Fri Feb 6 10:15:34 EST 2004

Check that you've bled all the air out of the coolant system.  If I recall,
the 4k is deceptively hard to get all of the air out - which leads to
I had a similar problem - The car would initially heat up, then the heat
would drop (t-stat opens, some heat lost in rad heat sink), then the heat
would climb until the car boiled over.  Problem: Blown Head Gasket in #5
(firewall end) cylinder was pressurizing the coolant system.  Check the
pressures in all cylinders - #5 was marginally out of spec in mine before
the head work.  One of the guys at the West Toronto Audifans meeting once
suggested that if you run the car up to operating temp (ie - hot) and then
pull the spark plugs and hold an inspection mirror over the plug hole - if
there's condensation that forms on the mirror, then you have a coolant leak
into that cylinder.
Leading up to the head rebuild, I was also told that the rad in my 5ktq was
blocked.  I took it out and flushed it with numerous nasty and not so nasty
chemical agents - yes, lots of gunk came out.  When I put it back in, it
didn't work that much better - putting your hand on the rad coils you could
feel the heat diminish when travelling away from the inlet/outlet end.  I
drove the car until, some time after the head rebuild, the rad failed
(couldn't figure out why the pavement was still wet under my car after the
rain dried) - the end cap cracked.  When I took the rad off (and replaced it
with a Modine brass rad/7 blade fan I just happened to have lying in wait in
the garage) - I removed the crusty old plastic end caps - lo and behold the
rubber gasket sealing the inlet/outlet side had a break in the part that
separates the in and out - result, some/most of the coolant was bypassing
the rad fins altogether.  The Modine went in and the temps dropped away from
being near 100C most of the time, to the mark in between 50 and 100. HTH
Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
(SPAM Blocker NOTE: Remove SHOES to reply)
----- Original Message ----- 
> Subject: Radiator fan switch 2
> To: quattro at audifans.com
>       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.
> 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.  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.  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.  I'm beginning to think its the
relay, but before I change it out, is there another switch, valve, relay,
etc or what ever that is regulating or not regulating this problem.
> Thanks

More information about the quattro mailing list