[s-cars] An overheating '93 UrS4

Fred Munro munrof at sympatico.ca
Mon Feb 21 21:17:49 EST 2005


Based on your post, I'd guess his thermostat has failed closed and his
heater core is leaking. The water pump may have a failed impeller, but that
would also limit circulation through the heater. If he's getting heat, the
water pump may be OK.

The only other thing that would match the symptoms is  frozen/slushy coolant
in the rad - how cold was it and how much antifreeze is he running?

Try emptying the coolant and pressure testing again. A small leak will leak
air more easily than coolant and show up more quickly as a loss in air

One area to check for a leak is the plastic air bleed screw in the hose
connection at the heater core. These tend to get brittle with time and break
and leak.

Those plastic impellers are crap. During my last t-belt job I returned the
"new" (rebuilt in Italy) Audi water pump to the dealer (it was also so tight
I could barely turn it by hand) and had them order an aftermarket pump with
a metal impeller and more vanes - higher pumping capacity than the Audi

Fred Munro
'94 S4

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of Igor Kessel
Sent: February 21, 2005 7:33 PM
To: Audi S-list
Cc: Lawrence Bardfeld
Subject: [s-cars] An overheating '93 UrS4

today my friend Larry stopped by to let me pressure test the cooling sys
in his '93 UrS4. Larry indicated that the coolant would slowly disappear
from the reservoir and within a week or two it trigger the alarm int he
central display. There was also a strong smell of coolant in the cabin,
only when the heater was on.

I pressure tested the car to 23psi. There were no leaks whatsoever. I
also checked the dipstick and the cap for foaming. There was no coolant
in the oil and there was no oil in the coolant. This pretty much rules
the head gasket out of the equation.

I took the car for a spirited a test-drive and safely made it back to my
garage half hour later. Larry was not so lucky. He left my house
shortly, but in 15 minutes I received a SOS call on my cellphone. To cut
the long story short Larry limped back into my garage an hour later in
the car that was overheating and spewing coolant from the reservoir cap
spout all over the engine compartment.

The symptoms are as follows:

1. The upper radiator hose is hot
2. The entire radiator is cold except for the tiny area around the upper
radiator hose
3. The engine idles at the second slim hash mark at 13:00
4. After a while the valve in the pressure cap blows releasing a geyser
of coolant
5. Heat is coming into the cabin, thus I am sure the coolant circulates
throughout the heater core
6. The lower radiator hose is cold

My immediate guess that either the water pump has lost or spun its
plastic impeller or the thermostat got stuck closed or both. Also the is
a leak in the heatercore and/or its hoses. Does anyone have any other

Igor Kessel
two turbo quattros
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