DIY: How to Replace a Thermostat on a 1999 Audi A8


1. Place a bucket under the radiator drain plug to catch radiator fluid. Unscrew the radiator drain plug with a socket wrench and allow the radiator fluid to drain into the bucket.
2. Use a screwdriver to loosen the screw on the radiator hose clamp connecting the hose to the engine. Pull the hose away from the engine and use the screwdriver to remove the thermostat cover.
3. Remove the defective thermostat and insert a new one. Make sure the thermostat faces the same direction as the old one--a reversed thermostat can cause engine damage.
4. Replace the radiator hose and tighten the clamp screw. Replace the radiator plug. Fill the radiator with coolant.