How to Repair a Thermostat in the BMW E39

1. Drain some of the engine coolant into the drain pan by opening the drain valve with a wrench on the bottom of the radiator.
2. Remove the bolts holding the thermostat housing on the engine with a wrench. You can find the thermostat housing by following the radiator hose to the engine. Pull the thermostat out of the engine and scrape away any remaining gasket material using a scraper tool.
3. Install the new thermostat into the engine, putting the spring side in the engine. Place a new gasket and the thermostat housing in place on the engine and tighten the bolts with the wrench. Fill the radiator and reservoir with coolant as needed.