BMW Thermostats for BMW 5 Series E39 (1996-2003)

The thermostat regulates the temperature of your coolant. At a predetermined temperature the thermostat will open to let coolant flow to the radiator and be cooled by airflow or the fan. Over time the thermostat will become stuck open or closed, leading to a variety of issues. A closed thermostat will never allow the coolant to reach the radiator and be cooled. Hot coolant will continue to circulate through the engine and absorb even more heat until boiling and the system overheats. An open thermostat is not as bad but is still not ideal - the coolant is always cool, with the temp needle always reading in the cool range. This tells the ECU to richen the fuel mixture to bring the car up to normal operating temp. So your fuel mileage decreases and the car runs rich.  

Replacing the thermostat is an easy but messy job. This thermostat includes the main o-ring (but a housing gasket may be required). Consider replacing the housing and any associated temp sensors while you're in there. The cooling system will need to be bled after.  

Most of the engines from the mid-1980s through the 1990s use the same thermostat design and they are interchangeable among the different temperatures. This is the 68*C thermostat, at the bottom of the temperature range. It should only be used in racing situations such as when deleting the engine fan. However, keep in mind that BMW spent a lot of time engineering the cooling system to work in all kinds of conditions and changing thermostat temperature is not recommended to fix any failures in the cooling system.  

Mishimoto makes coolant tanks, radiators and much more for your Mini/BMW. Established in 2003 their commitment to absolute quality in the aftermarket world is evident through the quality and performance enhancing products they offer.
 

This thermostat fits the following BMWs:   
1977-1983  E21 BMW  323i  
1986-1991  E30 BMW  318is 318ic 325e 325es 325i 325ic 325is 325ix  
1992-1999  E36 BMW  318i 318is 318ti 318ic 323is 323ic 325i 325is 325ic 328i 328is 328ic M3  
1982-1988  E28 BMW  528e  
1986-1988  E28 BMW  535i  
1989-1995  E34 BMW  525i 535i  
1997-1998  E39 BMW  528i  
1986-1989  E24 BMW  635csi  
1988-1994  E32 BMW  735i 735il  
1997-2000  Z3 BMW  Z3 2.8 M Roadster M Coupe