Coupe GT Cooling Systems, etc.

[Scott Fisher <sefisher@cisco.com>]

Dan Murphy asks about where to look for his hot-running Coupe GT:

Dan, the first thing you should do is flush the system several times
with a proprietary, aluminum-safe cooling system cleaner and water from
the hose.  While that's circulating in your system, look at three spots
in particular:

1 - the hose from the radiator to the overflow tank.  This is ultra
cheap (about 95 cents for a foot of tubing, plus I had to buy two
79-cent hose clamps too; in fact, I was surprised that I didn't have the
bits lying about my garage).  This hose is under a fair amount of
pressure and heat, two things that are unfriendly in the extreme to
rubber hoses.  The hose I took off had bulges, splits and tears near
both ends.  But it's crucial, as it's a key part of the system's
pressurization mechanism.

2 - the overflow tank cap.  This is also cheap (I can't remember how
much, it was part of a larger order I placed from Linda at Carlsen, and
now I too sing her praises).  Check yours: there should be two valves in
the center (inside) of the cap, one roughly flush with the cap liner,
the other standing proud of it about 3/8".  If one of them has broken
off and is now rattling about inside the cap (as was the case on my
car), throw the old cap away as soon as you get a new one.

3 - the fan switch.  Also fairly cheap ($8-9 or so through Linda) and
easy to install, this goes in the bottom of the radiator and is very
accessible through the LF wheel well.  If your radiator fan either never
comes on or always comes on, this is probably why.  In either case, your
car will not cool properly, and paradoxically, even if the fan runs
constantly it can contribute to running too hot.

I just finished a several-week-long odyssey into the cooling system of
my '83 Coupe GT, and found several things that may help you.  The short
description is that the cooling system is "backwards" from other cars
I've owned.  On the Audi, the thermostat is in the inlet of the water
pump, which takes water from the bottom of the radiator; the outlet to
the top (hot part) of the radiator comes from high in the block, NOT the
head, and it's unregulated.  The fan switch for the electric cooling fan
is located at the *bottom* of the radiator, meaning the whole thing must
heat to 95 degrees C before it closes the switch (and must cool to 90 C
before it shuts off, at least on the stock piece which I installed
yesterday).

It's almost as if -- and this is of major importance -- the cooling
system was designed NOT to shed excess BTUs, but rather to *ensure that
the engine was operating within a narrow temperature range*.

My advice: make sure everything in the system is working up to factory
specs.  This means, in ascending order of ease/expense of replacement,
to check out the little hose (1/4" i.d. hose can be made to fit, though
I think it'd be happier with 5/16"), the expansion tank cap, the fan
switch, and the coolant.  Oh, yes -- after you've drained the old crud
so that it comes out fairly clear when you pull the bottom hose from the
radiator, refill with a 40/60 mix of the Official Audi Coolant in plain
water.  It's... blue.  

As for cleaning the injectors, all I've done so far is make sure I fill
with Chevron, whose Techron additive package has been pretty well proven
to be that rare thing, an additive that does what it says.  (Though I've
never heard of Sea Foam, except as an ancient color option on Chevy
Biscaynes and the origin of the goddess Venus in Botticelli's famous
painting. :-)  You can also purchase various Techron products -- though
outside the western U.S. I don't know what brand markets them -- in
add-to-the-tank doses; I might have saved myself some time in cleaning
the system if I'd done that to a couple of tanks of gas, but the net
result is the same.  It does appear to make a difference, as the
hesitation (especially at high-end operation) and pinging I suffered
when I first took possession of the car -- when it had spent 98% of its
time unused -- have disappeared.  

Finally... just wait till you get it running right.  The Coupe GT is a
*very* sweet car, comfortably large inside and very compact outside,
smooth and stable on unpleasant roads but capable of *very* spirited
driving in the twisties, and in particular as a high-speed
freeway/highway tourer.  The five-cylinder engine makes a unique sound,
and is a willing and exciting performer once underway.  I originally
acquired mine as a temporary replacement for my "real" car, something
interesting enough to be worth having yet not *so* weird as to be
unusable, and as I've gone through the things the previous owner had put
on his "yeah, someday" list, I've come to love it.  It's become a
keeper.

--Scott Fisher