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1998 A3 1.8 Overheating

Old 10-06-2009, 10:22 AM
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Default 1998 A3 1.8 Overheating

Hi there,

This is my first post here and i'm hoping you can help.

A small while ago, my A3 started seriously overheating whilst driving - shooting up to pretty much the max (130+C).

After taking it to the local garage, i've had the Radiator, Thermostat and water pump replaced - the water pump's impellor had gone.

Unfortunately, this has not completely cured the problem. Using the 49c trick on the Air Con unit, I can see the temparature is still going up to 105C after moderate driving - a lot better than it was, but still not correct. When the engine isn't under load (e.g. running downhill), the temp does drop back down.

I've checked to see if the fans are coming on - the do not seem to be. Apparently switching the Air-Con on forces the secondary one on, but this is not doing the trick either. I'm assuming that due to the decrease in overall overheating, the new rad and pump are working, but are still not being sufficiently cooled.

Having done a search, I can see there's a trick / test where you bridge 2 pins on the fan to make the fans come on - unfortunately, I have no idea what this switch looks like or where I would find it.

Does anyone have any pictures or can they describe where I can find this?

Many thanks in advance!
Old 10-06-2009, 02:28 PM
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Join Date: Oct 2009
Posts: 3

Right, i've found the fan switch - bit of a bugger to find and get to!

I've also found the following test from

The test detailed is taken from the VW repair manual for the V5.
Caution keep hands etc away from the fans during this test as they are expected to run:

Reconnect both fan connectors, if still disconnected, and disconnect the 3 pin connector from the radiator fan thermo switch.
Bridge contact 1 and contact 2 with a short piece of wire, the fans should run at low speed.
Switch on ignition, bridge contact 2 and contact 3 with a short piece of wire, the fans should run at high speed.
Switch off ignition, reconnect thermo switch connector.

To identify the connector pin numbers, hold the connector facing you with connector latching mechanism at 2 o'clock, pin1 is then at 12 o'clock, pin 2 at 4 o'clock and pin 3 at 8 o'clock.

For anyone who wishes to try to test the thermo switch, low speed is switched on between 92 and 97 degC and the high speed switches between 99 and 105 degC.
It's now dark at the moment, so I won't be able to test tonight.

What i've also found though is that after driving home tonight (with a readout of 104C), the radiator was touchable - it was warm, but easily measurable by hand. This suggests either it's working amazingly well (doubt it) or there's no heated coolant going through it.

Does this suggest a Thermostat issue (even though it was recently replaced)? If the rad is not warming up enough, i'd assume that wouldn't be activitating the fan switch?
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