I have a 2002 Audi A6 Quattro 3.0L with 140k miles. Recently, it has been making intermittent noises after driving 30 minutes. It sounds like a engine rev without stepping on the gas. I also noticed that the coolant temp gauge has been going up over half way. On really hot summers, this may happen and I usually would turn on the heater and the temp gauge immediately dropped. This no longer works now. The temp coolant sensor was replaced at 122k. Any ideas on how to troubleshoot?

 

Aside from the temperature gauge being switched a while back, what other service has been performed on this car that you know about?

When was the timing belt and water pump changed, if at all? I am suspecting that your water pump is failing and there is little to no coolant flow within the system allowing the coolant to essentially boil.

It's also possible that there is an obstruction (IE thermostat stuck closed) but knowing a little more history about the service of the car would help narrow things down.

 

The timing belt, water pump, drive belts, and tensioner were changed at 108k in 2009. That was the only major service done.

 

I would suggest attempting to bleed the coolant system to ensure it's free of air pockets, then to check for flow from the top radiator hose, and once again bleed the system as you will introduce air once the hose is off.

I suggest this order because you will see if it's an air pocket issue vs. a no flow issue caused by a failing pump or an obstruction.

about 35,000 miles really isn't a lot of wear and tear, but stranger things have happened.