Hi all. I've recently been having a lot of trouble with my cooling system on my 1995 A6. One day, driving it up the side of a mountain (to a mountain biking spot) the heater core hoses blew off. Ok, no problem, I'll just tighten them down more. Not an issue. Well, it became an issue when I broke the plastic barb coming from the heater core. Ok, so what, I'll bypass the core till it gets warmer out and I can replace it more easily.

Here's the weird part. Today, driving up a different mountain again, I start smelling antifreeze and I open the hood to find steam coming from the cap on the overflow tank. But the problem was, the fans weren't even on, and the temperature in the car was at normal operating temperature. (1/3 of the way up, not even half way.)

The fans DO work, when I switch on the air conditioning. So I just switched it on and drove the rest of the way.

I'm not that familiar with my audi's cooling system. Is there a different temperature sensor for the fans than for the dash (like in old 12Vs)? Does that temp sensor go bad? Where IS that temp sensor? What else could be wrong? IIRC, in my corrado, when I turn the air on the fans come on HIGH, but when I turned it on in the audi, they didn't sound like they were on high. (I've never really looked at the fans while they were running on high...)

Any ideas? Thanks in advance.

I unfortunately don't have the Bentley for my audi, or else I'd just try everything they say in there...

EDIT: I recently did the timing belt on this car and while I was in there I replaced the water pump and thermostat. All of that stuff works dandy. (Hoses to the radiator DO get hot.)

 

How recent did you do the timing belt and water pump? Did you bleed the coolant system after you were done to ensure there was no air trapped in the system, thus preventing proper coolant flow?

 

Timing belt and water pump were done probably 6-8 months ago. All of that is fine.

 

This is going to sound a bit out of left field, but how high are these mountains that you're driving up? If they're a few thousand feet that you're climbing over the course of the trip, this could be something to consider.

I ask because this could be a clue as to the sudden onset of this issue. Water/coolant under pressure will boil at a higher temperature than 100C. At sea level exposed to 1 atmosphere the boiling temperature is 100C. At a higher elevation the liquid will require less heat/energy to boil, causing a tremendous amount of steam and pressure, which then in turn causes stuff to break.

If you're confident that there's no air left in the system after you did the timing belt, I'd have the system pressure tested to see what's going on next..

And to answer your question about the temperature sensors, yes, there are multiple sensors that the ECU uses to function. Namely the one on the lower side of the radiator is the one that controls the fans.

Also, I believe your A6 should have a belt driven fan. Is that functioning correctly?

 

The audi has electronic fans, not a belt driven fan. They work fine when the air conditioning is on. Otherwise I haven't seen them turn on. (I also haven't looked...) I've also never seen the temp of the car rise above the first bolded line in the temp gauge.