I’m the new owner of a 2011 Audi A4 – passed down from a family member who kept very good care of it. Several weeks ago during the first hot weather blast, it started overheating when I was sitting in traffic with the AC on. Coolant level was very low, but after filling that up (using the correct coolant for an Audi), it continued to overheat in the heat, again only in stop/go traffic. I know very little about cars, but per a friend’s suggestion, I turned the heat on driving to/from work, which helped as did the couple weeks of cold, rainy weather that followed. Very hot weather is starting up again, and it overheated the other day (same circumstances) — I cranked the heat, and as soon as I’m able to get moving this seems to help the most/cool the engine down. The coolant is low again, but I’ve checked for fluids underneath my car multiple times, and it doesn’t appear to be leaking anything. From what I’ve read, it sounds like it’s either the thermometer (cheap part, $$ labor), or the water pump (expensive all around). I’m wondering if this sounds accurate, what I should expect to pay for either of these, and any recommendations for a foreign auto repair shop in the Somerville, MA area! Any suggestions/tips are greatly appreciated!
Has anyone checked if the cooling fans for the radiator are turning on?
Tester
No… I haven’t taken it anywhere yet. I’m both unfamiliar with cars/audis, and in search of a rec. for a reputable repair shop— I’m hoping to head to one with an idea of what may be going on. I haven’t seen this yet (in my limited research/asking around) so very much appreciate this suggestion!
You can check for fan operation yourself.
Open the hood.
Start the engine.
Turn the AC on.
Get out and look if any of the radiator fans are running by looking at the back of the radiator.
If the fans aren’t running, that’s the problem.
Tester
Oh… sweet! So, when I’ve opened my hood before (to check the coolant), it looks like much what is under there is almost covered (for lack of a better word) by a plastic shield. That’s probably inaccurate, but the best way I can describe it… should it still be relatively easy to see if it is the radiator fans??
It’s called a decorative engine cover.
You should be able to see/hear if the fans are running without removing the cover.
Tester
Awesome, thank you so much!
@hallorymogren In the red banner at the top of the page click on the words ‘Mechanics files’ to see reviews of repair places near you.
So helpful— thank you!
I believe @Tester is right, but the loss of coolant is troubling. You may also have a bad radiator cap. I would just replace it because even if it isn’t bad yet, it will be soon. That may not stop the overheating but it might reduce the coolant loss.
If turning the AC on causes the fans to come on, that only means the fans are good. There is also a thermostatic switch that turns the fans on when the AC is off and the coolant exceeds a preset temperature.
Next time it starts overheating, turn on the AC first to see if the temp drops. If it does, then the fans are good but the thermostatic switch isn’t. There are also two or three relays in the circuit and one or more of them could be defective. A good shop should be able to isolate the defect pretty easily.
The good news is that cooling systems in water cooled engines all operate using the same principles. And they have not become highly computerized like ignition and fuel metering. Your Audi, while it might have a few unique names for some of its cooling system components, can be properly diagnosed and repaired by any competent shop. I might take a bit longer to get parts in, as they may not be as readily available as those for a Chevy or Ford, and the parts may cost a bit more, but the diagnostic and repair protocols and technologies are well and long established.
Turning on the heat helped, because it dissipated a bit of the heat. And I highly commend you for not only refilling the cooling system rather than just driving on, and for using the correct coolant. Too many not-so-serious cooling system problems have been made into disasters because the drivers put whatever was cheap in the system.
I feel it necessary to comment on the AC system and the fans. In many cars there are two cooling fans, one to provide airflow for the AC system and one to provide flow to cool the engine’s coolant. In some cars with one fan, the fan operates at all times when the AC is on and only in response to the heat sensor when it isn’t. In the systems with two fans, turning the AC on will provide fan-driven airflow through the radiator when the AC is turned on even if the “primary” fan is dead, although the heat will not be as effectively dissipated. With respect, I cannot agree that turning the AC on and having the system temperature drop necessarily means that the fans are good. It may only mean that one fan is good. Can’t tell without looking at it.
In short, the problem needs hands-on diagnosis. I congratulate you on having used good sense to this point. Keep up the good work. Let us know how you make out.
You need to find out where the leak is. A pressure test can be done to try and figure that out. Anything in the system could be leaking from radiator to hoses to water pump. For the over-heating, if the fans are coming on, and if the thermostat is ok, and your fluid level stays up, you could have a bad radiator or one filled with bugs so it can no longer dissipate the heat. Even though it was taken good care of, it’s possible nothing has ever been done to maintain the cooling system and Audi repair is expensive.
My early 90’s Corolla has had that same symptom a couple of times over the years, and the cause has always been the coolant temp sensor that turns the radiator fan on has failed. In one case the overheating blew a small hole at the top of the radiator too, causing some coolant loss. There was no dripping of coolant on the ground though when that happened, as it was a small hole and probably was evaporating rather than dripping. I could see a little coolant puddling at the bottom trough where the radiator sits though.
Next time it overheats, pull over (providing this is safe of course), leave the engine running, and pop the hood and check to see if the radiator fans are spinning. They should be spinning like crazy. If not, that’s the problem. Once you get the fans working properly, you’ll have to have the shop investigate what’s leaking too. The cooling system won’t work properly unless it holds pressure to about 7-10 psi. There’s a pretty good chance you’ve blown a small hole in your radiator too, just like mine. It wasn’t much of a problem for me, I think the new radiator cost $90 and it took me maybe 1 1/2 hours to install, a very simple job. Best of luck there OP.
I think the OP is lacking technical expertise to diagnose cooling issues if they can’t even find rad fans. Time to bring car to an Audi/foreign shop
Cavell, you may have a point there. 
Except that a foreign car specialist probably isn’t necessary for a cooling problem. Fortunately, the cooling system that hasn’t yet gone too high tech for any good shop to diagnose and repair. At least on gas-engine cars! 15 years from now when 60% of new cars are sophisticated hybrids, perhaps even hydrogen cars, and the other 40% are EVs, cooling systems may have evolved to where only specialists can diagnose and repair them. Lithium Ion arrays, or whatever will be the common energy storage platform 15 years hence, will probably have cooling systems that will be beyond the scope of the average shop. Hopefully I’ll still be driving my '05! 
Thanks for all those who provided helpful advice and support! I did get my car to a foreign repair shop asap, but also wanted to be sure I had some idea of what might be going on seeing as I am-- without a doubt-- lacking technical expertise, and have a slight paranoid fear of being totally screwed over by most mechanics. Turns out, the problem was with the wiring to the radiator fans — it was all labor and no parts. Overall, better than I was hoping for. The mechanic seemed to imply that somebody was “in there” before, possible (and maybe by accident?) doing something to the wires, but I’m 99% positive the only other repair shop this car has been to is the Audi dealer. Anyways-- thank you again!
…or, the wires might have been gnawed-on by a rodent.
It does happen!
A VW dealer make a mistake in a re-wiring job on my old Rabbit years ago. Such a thing can happen, even at a dealer shop. In any event, glad it was just the fan wiring and you are now back on the road with a cool running vehicle.