clandrum07

I have a 2001 A6 with the 4.2l engine with a cooling issue. I was sitting in a parking lot one day with a/c on. I had drove it majority of the day and didn't have any issues. I had been sitting there I guess 15 minutes and I noticed the car was running hot. I let it cool down and limped it to my friend's house. While it sat there cooling down, it dumped all the antifreeze out of the overflow. After trying to figure out what happened, I realized the coolant tank cap was broke. I replaced it and it worked fine. Next day, it was running one notch past the middle mark. After speaking with a mechanic, I found the coolant tank was cracked in multiple places. Still runs one notch past the middle. I have flushed the radiator but cannot find the coolant bleeder screws anywhere. I found the radiator drain plug near the driver's side fog light. Not sure really what else to do or what else it could be besides air in the system. This is the 1st German car I have ever owned. Any help/advice is greatly appreciated. I have spent nearly 2 hrs looking for any answers and can't find anything.

4Driver4

Thermostat is a common failure. How old is the timing belt?

clandrum07

Not sure. I've only owned it for 6 months.

SloopJohnB@mac.com

Interesting...my 2K4.2 and 02S6 do not have drain plugs for the radiator...one drains the radiator by using the quick disconnect on the bottom radiator hose connection to the radiator.

That being said, there are several things that could fail causing overheat:
1. viscous clutch engine-driven fan.
2. Thermostat
3. leaks, low coolant (expansion tank cap, leaking expansion tank, cracked line from upper radiator hose to expansion tank..BTW...I would replace that plastic line if you replace a cracked expansion tank!!
4. Auxiliary cooling fans not...either the fan is toasted or the the fan module has failed.
5. low prob...radiator temperature thermoswitch.

If your oil temp gauge is sitting around 225 but the coolant temp is one notch above straight up, you're probably ok...when the oil temp climbs over 250 and your coolant temp is up there it's time to cool off.

And use synthetic oil no matter what anyone tells you. The synthetic oil can save your overheated engine.

How many miles on the car? if it has over 75K on it chances are it's time for TB service.
Don't forget the serpentine belt!!! If it has over 140K miles on it change the voltage regulator/brushes on the alternator--likely brush wear is below 5mm limit.

clandrum07

It has about 157k on it. All fans are working and there is no leaks. Oil temp is fine. I always run synthetic oil in all my cars. The plug I found is a blue plastic screw on the bottom corner on the driver's side of the radiator. It is visible after you remove the fog light grill. I located it after reading another post on here but there wasn't anymore details and it was 3 years old so I started a new post. I hope it doesn't need a timing service lol

mithrilG60

If your car has 157000 miles on it and you don't know the service history of the TB then you definitely need a TB service just to be on the safe side. One of the issues addressed by the TB service is the fact that the OE waterpump had a plastic impeller which would crack and detach from the pulley over time leaving you with no visual indicator but a water pump that is effectively useless at circulating coolant... obviously that would affect your engine temps

Have you replaced the expansion tank? Could be that your cracks and failing cap are preventing the system from fully pressurizing which compromises it's ability to absorb heat. I replaced mine earlier this week as the seal on the 2 halves was starting to go (very slow seep of coolant) and discovered a couple cracks forming on the underside at the same time. The new tank and full system pressure has resulted in dropping in my oil temps by a good notch on the dash gauge so the coolant was obviously not being fully pressurized before.

If you're thinking you have air in the system the bleed process is dead simple as the design all VW/Audi coolant systems which places the expansion tank at the highest point of the system makes them self-bleeding. Just remove the cap from the expansion tank and idle the car up to temp. As the thermostat opens it will suck fluid in and any air will automatically be expelled via the tank. Now top coolant up to level.

Other than that you can test the thermostat by grabbing the upper and lower rad hoses once the engine is at temp. If your thermostat is stuck closed there will be a noticable temperature difference between the upper and lower rad hoses.

NJA642

No bleed screws on our year/engine, but we do have the blue coolant drain petcock that you found.

There is a bleed hole in the top hose going through the firewall to the heater core. (next to the battery). There are some silver markings on the rubber. Pull that hose back off the fitting so the hole in the hose lines up with the hole in the fitting to bleed. As mentioned, tank is high, so you are probably ok with just idling w/ the cap off and heat on.

Oil Temp remaining stable might be a positive indicator. Could this be a sensor/gauge issue?
Do the upper/lower hose test. If they are the same temp, look into WP/Thermo (both are behind the t-belt). If there is good differential, look at the sensors.

mithrilG60

I think you mean the reverse. A significant difference in temp between upper and lower at operating temps usually indicates that the thermostat has failed to open and therefore allow coolant into the rad meaning you're not getting real cooling effect.

NJA642

UHH... yeah, thats what i meant... no/low-flow condition vs. adequate flow condition.