overheating 4000q

[George Nimmer]

Thanks Huw (love the web page BTW!).  My thermostat is the 87 degree
celsius model, which sounds like a high opening temp to me, but It's all
my mechanic had in stock.  When I installed it, I found that the one
that was in there was a cheap made-in-taiwan model, unlike the German
made one I was installing - however it was also an 87 degree model.

Perhaps I just need one with a lower opening temperature?

Thanks
George

On Wed, 2002-09-11 at 00:54, Huw Powell wrote:
>
> > I have a puzzling problem with my '85 4000s quattro overheating.  It has
> > 156k miles on it.
> >
> > The overheating only occurs when the outside ambient temperature is over
> > 90 degrees Fahrenheit, and only when traveling for 15 minutes or more at
> > greater than 70 mph.  When this happens, the water temp needle slowly
> > climbs to almost the top of the gauge, and very shortly there after, the
> > oil temp climbs until the little red LED at the top of the bar lights
> > up.
> >
> > Again, it only overheats when driving for 15 mins or more, at greater
> > than 70mph, when outside temps are 90+.  It does this whether or not the
> > A/C is on.
> >
> > It runs cool as a cucumber when the A/C is on high and I'm stuck in
> > traffic, driving in the city, or crusing at only 60mph, even when
> > outside temps are 100+ degrees.
>
> Ok, that is totally weird.  [scratches head in frustration]
>
> try this... although at those speeds, your fan should never come on
> anyway, when your AC is on high the rad fan is automatically engaged via
> other means.  You should test your coolant switch in the bottom of the
> radiator i guess.
>
> unplug it, short the wires.  fan run?  yes, pull sender and test.  no,
> find fan problem and fix.
>
> test sender with boiling water and ohm meter (it closes around 200 dF).
> get new one, install.
>
> But it's not really AC related, just 70 mph+ related... darn.
>
> Maybe your cat is clogged...?  You start working the engine hard in one
> of those bricks at 70, and if the exhaust can't get out nicely it starts
> warming up the engine...
>
> > I have replaced the water pump, thermostat, coolant expansion tank, all
> > coolant hoses, the radiator, radiator fan, water temp sender, and
> > flushed the coolant more than a few times.  I'm running a 50/50 mix of
> > distilled water and G12, and there are no leaks in the system.  In
> > addition, I had the coolant system pressure tested at the local VW/audi
> > independant shop, and had them ensure there were no air bubbles stuck in
> > the system.
> >
> > What other components could I possible check???
> >
> > The engine starts and runs marvelously, revs cleanly and smoothly all
> > the way to redline.  it is meticulously maintained, and I've taken
> > several recent ~500 mile drives without any problems whatsoever (with
> > the exception of the aforementioned overheating under certain conditions
> > situation).
>
> --
> Huw Powell
>
> http://www.humanspeakers.com/
>
> http://www.humanthoughts.org/