How to Replace the Thermostat on the 2000 Audi A4

1. Remove the bolts that secure the engine skid plate to the bottom of the engine using a socket and ratchet. When you remove the skid plate, you will expose the bottom of the radiator and the water inlet housing.
2. Remove the red radiator pug with a pair of pliers and drain the contents of the radiator into a drain pan. Push the red plug back into the radiator after you are finished.
3. Follow the lower hose to locate the water inlet housing. The hose connects to the housing.
4. Remove the two nuts that secure the water inlet housing to the water pump using a socket and ratchet. Pull the housing off the water pump while still attached to the hose. Wipe the mating surface of the cover off with a clean towel.
5. Pull the old thermostat out of the pump.
6. Place the thermostat gasket onto the housing of the new thermostat. Coat the surface of the gasket with coolant.
7. Slide the thermostat back into the water pump. The end of the thermostat with the spring goes into the pump.
8. Place the water inlet housing onto the water pump, thread the nuts back onto the water pump studs and tighten them with the socket and ratchet.
9. Open the radiator cap, place a funnel into the filler spout and drain the coolant back into the engine.
10. Place the engine skid plate against the bottom of the engine, thread the bolts into place and tighten them with the socket and ratchet.