Troubleshooting

• You can test your thermostat by removing the radiator cap and sticking a thermometer in the hole. Crank up your Audi and observe the temperature when the water starts to circulate. The water should circulate at the rated temperature of the thermostat, usually around 195 degrees. If the water is circulating while the engine is cold, then you know the thermostat is stuck open---and so it's time to replace it.
  
  

Replacing the Thermostat

• Follow the top radiator hose and you will notice that it runs to the top of the engine block to a housing. Inside this housing is where the Audi's thermostat is located. To access the thermostat, you must remove only two bolts with a ratchet and then remove the radiator hose with a flat-head screwdriver. The housing will come right off. You can just pull the thermometer out with your fingers.
  
  Replace the gasket as well; it's no good after you've broken the seal of the housing. The new thermostat will come with a fresh gasket. The thermostat is usually marked to help you remember what end goes up and what end goes down---that's an important distinction.
  
  

When to Replace the Thermostat

• It is always a good idea to remove the thermostat and replace it when you perform maintenance on your Audi. At the very least, replace the thermostat every 100,000 miles or whenever you perform your routine maintenance on the cooling system. Definitely replace the thermostat if you notice your car is starting to overheat; it's usually one of the first things to be replaced in those cases.
  
  Having a new thermostat will ensure that your heater is always ready to come on when you need it and that the water is flowing at optimal temperatures required for your Audi to operate efficiently. It will also prevent overheating if you are in stop-and-go traffic. In some cases, you can run your car without a thermostat, but it's not advised in case you ever need to run your defroster or heater.