'97 A6 Avant Quattro Wagon - 2.8L - Automatic - 129k Miles

I just inherited this car so I have a bit of unknown on the overall history.

Issue: The coolant backs up into the overflow and pukes all over. However, it only does it after taking it for a test drive and will NOT do it while just idling. I have let it idle for over 90min and it never overheated, puked coolant or showed any other signs of distress.

Troubleshooting: I have bled the system profusely. I have used the bleed screws on the pipe at the firewall and the one on the back of the left head/intake. There is no more air in the system and it flows only coolant when either is cracked. I have pressurized the system and there are no leaks. It has a new cap on the tank.
I have let it idle for over 90min and zero issues. Temp gauge is straight up, no indicator lights and no leaks or pressure issues. If I take it for a test drive, just around the block, the coolant will start to back into the overflow and puke. The temp though never spikes.
Also, the lower radiator hose on the right never gets hot but the upper on the left does. The interior heat is also blowing nice & hot as I have the heater on hot while bleeding the air and it never varies in temp when idling vs driving.

Thoughts??: I am thinking this has to be either a water pump (impeller issue) or thermostat (less likely since the temp comes up and it blows hot air in the cabin).
Any other thoughts? I don't believe this is a head gasket issue because I can't see how driving vs. idling would make a difference with a gasket.

Any input or suggestions would be welcome. Thanks from a new Audi owner.

 

As far as the water pump, the only job of this is to create flow. Pull a hose off and run the car see if you have coolant flowing, if you do then fine pump is good. Sounds like your thermostat is stuck, or possibly the heater core is clogged. Try flushing the system and replacing the thermostat.

 

Correction, if you have flow and the WP isn't leaking don't replace it. Unless its over a 100k and never been done before then i would.

 

I put the stats of the car at the top of my post. It has 129k on it currently and I don't believe the WP has been replaced although, like I said, this is new to me and I don't have a good history yet.

As for the heater core being clogged, would it still blow hot in the cabin if that was the case? This seems to be counter intuitive so please correct me if I'm wrong.

I am thinking at this point that I do the WP and thermostat. I'm still not convinced of the thermostat, since the water temp comes up according to the gauge, but it could be a possibility. There is no leaking but I do know, from my VW Jetta, that the impellers & shafts on the WP are notorious for failing.

If there are any other ideas or suggestions please let me know.

 

Have you checked to see if your radiator is clogged? remove upper and lower hoses and try running water through the rad. The coolant system is supposed to have a few psi pressure going through it. sounds like you are getting overpressure. leads me to think there is a clog somewhere, especially since you mention that the lower hose never gets warm. if there is a back up in the rad, the waterpump will be pushing more coolant into the tank than can flow out through the radiator and then....puke.

that is what comes to mind anyway.

good luck

-not an expert just an enthusiast

 

Remember, one of the main points of my symptoms is that it only pukes and shows signs of distress when I take it for a test drive. After 90 minutes of idling (very long time) it NEVER had any issues. I took it around the block and only made it half way before it started to back into the overflow.

So, does the radiator clogged still make sense? Not saying it doesn't but I want to make sure everyone is keying in on this piece of the puzzle and it seems key to me.

 

well, this is how I'm thinking about it...

waterpump runs off the timing belt, which runs off the crank pulley. higher RPMs spins the crank faster, spins the impeller faster, moves more coolant (faster). if there is a restriction in the system, the coolant has to go somewhere....

 

I had the same problem with my 97 2.8 12v. I replaced the Thermostat and Water pump (did it on my own, if not I would be broke >.<)...didn't fix the problem. I had a **** ton of rust in my coolant, turned out my Radiator was no good due to the rust im thinking. I replaced my radiator and problem fixed.

 

Same here. Rust colored puke after 90 minutes and 110 degrees plus weather here in Austin, TX.

Turned out to be mainly caused by radiator, but also did the water pump (plastic impeller!) and thermostat (and timing belt +rollers+tensioner).

Clogged with rust both radiator and thermostat.

My 2000 A6 now cycles the electric fan off and on! No more leaks.

Also check for broken fan blades on the non-electric fan. I had 2 busted off.

The DIY's are a god send and have saved me plenty of $$$.