Is it common for audi's with 4.2's or any Audi for that matter to overheat in traffic with the a/c on? I had an issue last summer when i would find myself in bad traffic on a hot day with the a/c on the car would begin to creep past the middle and up to the "H" if I didnt turn the a/c off or start driving on an open road. Ive replaced my thermostat already and the issue still exists.

Now a friend of mine picked up an A8 with the same motor and he has the same issue. His thermostat is reasonably new as well. Ive searched here and other forums and the common answer is thermostat and temp sensor. But these have been replaced to no avail and, I dont think the thermostat would only cause a problem while standing still.

Is it possible that the electric fan that comes on with the a/c is too weak? or maybe just worn?

Does anyone else here have this problem?

 

Could have a small leak somewhere


Overheating in traffic is usually related to the coolant temp sensor or fans/fan clutch. If you've already replaced the CTS, I'd definitely start investigating the fan clutch.

No expert though, so try to check with a vet or another 4.2 before doing anything drastic.

 

Make sure all the radiator cooling fans are running when the temp is going up. If they are, look at the temp sensor and the thermostat. Be sure the cooling system is filled and not leaking, bleed the system to insure there is no airlock going on (if the system ever was opened and not bled, this could be the problem). After all that, you could have a blocked radiator which is hard to diagnose, you just eliminate everything else and then replace it.

 

Forgot to mention that the waterpump may have an impeller failure (missing or damaged vanes) and need replacing.

 

I had a similar problem and it ended up being the radiator clogged up. Ran some pressurized water through it while doing the TB and I got it unclogged without having to replace it ...30k miles later still running fine without any overheating signs at all.
Same engine btw c5, 4.2

 

As oldmots already mentioned, the fans are kicking in based on the thermo switch/sensor's temp read. If the fans never start that would be another culprit to investigate.
This isn't the the CTS you already replaced - it's another one that screws into the radiator (lower side of the radiator, driver side is the general area).

 

I just got it one mark past the center and pulled over. The electric fan behind the radiator was not running, but electric fan infront of the radiator was. Im pretty sure that at that temp all the fans should be running. Im going to look into replacing that switch. Thanks for the input.