2001 tt coupe 225 quattro. Started showing one notch to the right hot on the temperature gauge. Replaced temp sensor with green top. Gauge still showed hot. Checked code 49 and it shows 104 c on highway at 60 mph. Flushed coolant and replaced. No change. In 5th gear at 60 mph, temp drops to 101 or 102c. In 4th gear at 60 mph, temp drops to 99c. Fans are working fine. By the way, code 51 (oil temp, I believe) stays a constant 90c. What do you guys think? Water pump? Thermostat? I'm wide open to suggestions. The car is driving fine otherwise.

 

ah man, I just had an overheating problem, I just replaced my thermostat and went to Audi and brought the dealer coolant, all is fine now...i was told not to use any other coolant but from dealer, so that the car can run cooler, so right now my engine temp needle is right in the middle.

 

The OEM thermostat is 050-121-113-B for 22.50, O ring 038-121-119-B for 1.78 and a gallon of coolant G012A8G1G is 16.50 all in stock. Plus UPS ground shipping.

My experience is at the same 60 mph freeway speed what gear you are in will change the rpm's but not the airflow through the radiator. At 60 mph and higher rpm's this will demand more from cooling system, but for normal driving in traffic for example, the air speed through your radiator is more than the electric fans would pull. What are your temps when driving in the city under say 45 mph? I'd assume you'd have said something if that was a problem. A bad thermostat will cause overheating no matter what the mph is, or if open all the time would run colder than it should most of the time.

Take a look at the underside of your water pump. There is an inspection hole behind the pulley. If you see corrosion or wetness then the pump is bad or going bad, but is probably not the cause to your problem. A friend had a strange cooling system problem on a non Audi car. When we took the pump off, the impeller was not pressed on the pump shaft. It had loosened and spun, so was not pushing coolant through the engine as it should. Only found that after doing the thermostat and flush. That was a strange one.

 

thanks, guys. I'll change the thermostat. Hope that's all it is. By the way, Jeff, it runs a little cooler in town, unless I come to a complete stop. At a traffic light, etc., the temperature begins to creep back up.