The engine coolant thermostat for the BMW 3 Series B46/B48 engine is an electronically controlled map-controlled thermostat. Unlike conventional thermostats, this unit receives signals from the ECU and opens at variable temperatures between 80°C and 107°C depending on load, improving fuel economy and reducing emissions.

1. 1
2. Allow engine to cool fully
3. 2
4. Drain coolant below thermostat level
5. 3
6. Remove intake manifold cover
7. 4
8. Locate thermostat housing on engine coolant outlet
9. 5
10. Disconnect coolant hoses
11. 6
12. Disconnect electrical connector
13. 7
14. Remove 3 housing bolts (8mm)
15. 8
16. Remove old thermostat and gasket
17. 9
18. Clean mating surface
19. 10
20. Install new thermostat with new gasket
21. 11
22. Torque bolts to 10Nm
23. 12
24. Refill coolant and bleed system.