I just purchased a 1996 Audi A6 Quattro with 90,000 miles on it. I purchased the car in Florida. During the test drive before purchase I tested the Air conditioning, heat, etc. and the AC was ice cold and all heat functions worked well blowing different levels of heated air. During my test drive in Miami on a 70 degree afternoon with the A/C on, theinstrument panel temp gauge needle hovered in thelast line in the "C" area of temp gauge. I was pleased with the car runningvery cool with the AC on full blast and the needle never went past the quarter mark on the gauge. I also have a 1995 A6 FWD and the temp needle sometimes goes to the half way mark on a hot day.

My dilemna is this. I drove the car 1200 miles to the Northeast home over the weekend. The outside temperature was about 25 degrees F during the entire drive and the temperature needle was pegged at the very left or bottom of the scale (barely making it to the first line in the "C" section of the gauge). The heat blew very hot air if I asked it too, as I went through the different temperatures so I assume the thermostat was not stuck. After my first fuel stop (averaging only 20MPG by the way) I fueled up and checked under the hood and the entire engine, including hoses, radiator, intake manifold, coolant resevoir, etc. was slightly lukewarm at best to the touch. My other A6, after the same workout would be extremely hot and would burn the heck out of my hands if I touched the radiator, hoses, etc. I thought this to be a bit unusual and began thinking of possible causes. The car performed perfectly in all aspects during the entire 1200 mile trip with no oil consumption, loss of coolant, etc.

The two symptoms of this car that are baffling me are the extreme cool running temp of the engine and the less than optimum Miles per gallon the car is achieving at highway cruising. Is this even a problem or something to be concerned about? Maybe the previous owner installed a very low temp thermostat to make the car run cool in the scorching Miami heat??? Are the two related? Anybody else have this experience or can give sound advice?

Sidenote: I also have a Porsche 911 and when I adjust the Air Fuel mixture on that to lean it out, because as we all know "Lean is Mean" if I adjust it too lean the engine, exhaust manifold, etc. gets so damn hot it will literally melt paint on body panels in close proximity toexhaust components (don't ask me how I know this!). On the flip side, if the car is running too rich (hence the poor gas mileage) will that cause the car to run extremely cool providing the thermostat and all other functions are working properly? Any thoughts? Thanks.

PS: I have no idea on how to adjust the Air/Fuel mixture on the A6.

 

I would bet money that the thermostat is stuck open if the hoses only feel warm to the touch after a drive like that. Its very common on the V6 engines audi makes. I would definately check to see if the timing belt/water pump and thermostat has already been replaced considering your at 90k, that service should be done around the 80k mark. (because of timing belts breaking)
You should also replace the CTS (coolant temp sensor) because those are commonly bad and can cause severely bad fuel mileage and gauge fluxuations. To find the CTS sensor (assuming you have a 2.8L) take off the plastic intake hose on the back of the engine and the sensor will be sitting right behind the engine on the passenger side, if its black, definately replace it.

As for the air/fuel mixture, you can't adjust the mixture because its all done by computer, so don't worry about that. Its running very rich right now because the temp isn't reaching operating temp sothe computer isn't going into "closed loop" which means it uses the O2 sensors to adjust fuel. A bad CTS sensor can also keep the car in a very rich state which is not ideal.
You should be averaging 25-28 MPG's on the highway with a 2.8L engine.
If you know a good mechanic that knows audis, then buy the timing belt ultimate kit from www.ecstuning.com which has everything you need to fix the car (except the CTS sensor which can be bought seperately) Good luck.

 

Great advice and thanks for the response Auditech79!

One last question, the car dealership where I bought the car had no service records on the car available. I specifically asked if the Timing belt, water pump, etc. has been replaced and the dealer did not know. I searched around the engine compartment for a sticker or decalfrom any dealer and/or shop that many good shops place under the hood to indicate the date and mileage the timing belt was replaced but did not find one. My hunch is the timing belt was never replaced. However, just to be sure, is there any other way or visible clues (without taking car apart) to determine if the timing belt job was done on the car? Thanks again.

 

Well you can pop the top of the timing cover loose and take a look at the belt, if there are white lines on the "outside" of the belt then its probably been there a while.

 

I had same symptoms on '95 A6 for 2 years. Removal of the Thermostat showed that it would never fully close when cool. Coolant would run thru radiator as soon as engine started. Thermo was only open about 1/16" but that was enough to create the exact same symptoms as you have.

I replaced thermostat Jan 2, 2008 and now it is running fine. Tested it for 50 miles with water only before draining, flushing and then adding Pentosin G12 with distilled water. 50/50 ratio.

Now have lower idle speed when warmed up, better acceleration and maybe better gas mileage.In addition, temp gauge reads correctly now when engine warms up, about 40-45% of full scale. And that needle stays right there in city or highway speeds.

The Electronic Engine Coolant Temperature Thermal Switch sometimes called ECT was not the problem. There are two ECTs on the 1995 A6. Caution that you are checking the one with 3 wires not 2. The 3 wire unit on the passeger side rear of block and under plastic air hose, controls dashboard temp gauge in addition to other things.This 3 wire ECT on 1995 A6 can be checked with an ohmmeter from terminal [ T ] to ground. Also, a 40 ohm resistor from engine ground to terminal [ T ] should make the temp gauge read about 40-45% of full scale.

 

Excellent info ne2q 73, except his car doesn't have the two controllingECT sensors, just one. Pre 95 A6's are all equipped with the two sensors like you explained.

 

Yes Auditech79.....I had no idea if the '96 had 2 ECT or one. That is why I mentioned my '95 A6. Thank you for that info.

I just posted some photos of my A6 radiator drain location, the actual Engine Coolant Drain plug that is under the back side of engine and a photo under engine showing the recess where the drain plug screws in. I did get quite a bit more coolant out thru that drain.

 

Jaybird, I think I bought your 1996 A6, and it is funny that I would find your post based on the same question that I have about the car. Did you ever find out why your car is running so cold? Ant