RE: Radiator Fan Afterrun

["Avi Meron" <avi@cosmoslink.net>]

Look at this post from Alex.
Avi


Hi List,

It seems that many 5KT(Q)s are plagued with a charging/battery problems.
The common explanation is that those cars, while having many
current-consuming accessories, have only 90amp alternator. What I noticed is
that actually the biggest battery-eater is the afterrun fan, which usually
runs for 10-15min every time the engine is switched off at operating
temperature. It does not cause problems if the car is used for long highway
trips (the alternator has plenty of time to recharge the battery), but if
one uses the car mainly for short trips around the city (like I do),
particularly with some accesories on, the alternator doesn't have time to
recharge the battery, and since battery is usually left in discharged state
for most of the time, it's lifespan is severly reduced.  Apparently, Audi
knew about the problem. They changed the alternator to a stronger 110amp
version on late MC engines and changed the afterrun fan thermoswitch to one
operating at higher temp on 3B engines. After buying 3rd battery in 4 years,
rebuilding the alternator, putting new voltage regulator, replacing the fan
thermoswitch, having found the wiring to be OK and being *really* tired of
having to constantly worry if the car will start, I came to the conclusion
that this indeed is a desing flaw. While I understand the importance of
cooling the turbo after shutoff, I think the 10-15min of cooling action
*every* time the engine is at operating temperature (not only after
"spirited" driving) is just way too long. There is a time limiting device
incorporated into the electric coolant pump, but it's set from factory to
about 20min. My fix reduces this time limit to lower value.
The electric coolant pump/afterrun fan relay is located on an additional
relay panel under the acces flap on left side of the dash. See the
schematics on the access plate for exact location. After removing and
opening the relay you'll se a circuit board with lot of transistors,
resistors and one 220µF/16V electrolytic capacitor. This capacitor is
responsible for the time limit. I replaced it with 47µF capacitor (NOTE
POLARITY before desoldering and use 16V or more capacitor) and now the fan
runs for about 3 minutes. I believe it's enough to cool the turbo and the
starter spins the engine happily at full speed every time now. If you feel 3
minutes is not enough, use larger capacitor.
Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.com.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)

-----Original Message-----
From:	owner-quattro@coimbra.ans.net [mailto:owner-quattro@coimbra.ans.net]
On Behalf Of JJK1204@aol.com
Sent:	Tuesday, January 05, 1999 1:24 PM
To:	quattro@coimbra.ans.net
Subject:	Radiator Fan Afterrun

On my 87 5ktq the electric coolant pump is missing and the radiator fan runs
for a long time after the car is turned off (after what I am led to believe
is
the couple of minute soak period). I have a new battery, but this morning it
wasn't powerful enough to start the car (-16 degF). How can I diable the
afterrun radiator system or at least shorten it by 3/4?

John Katos
87 5000cs TQ