E46 Cooling System Thermostat Replacement
These instructions are only a guide for replacing the thermostat. Please read through all the instructions before attempting to install on your own. I take no responsibilities for any inaccuracies or problems/damage /injuries you may encounter from using these instructions. Please consult your shop manual.
When the thermostat starts to fail, it typically fails stuck open. Symptoms are your car takes longer to warm up. When driving on the freeway, you may see your water temperature gauge swing to the cold side. The service "Service Engine Soon" light may come on informing you that your engine is operating out of temperature range. On my car, the error code was P1624. There are other error codes that will signal same issue.
Thermostat (Part # 11537509227) (Figure A)
(Check BMW for latest part #)
Pan to catch the old Coolant
For Cars with Automatic Transmissions
You need Clutch Fan removal tools. This is not covered in this DIY
1. Raise front of the car and remove underbody splash guard. Its held in place by screws and some plastic plugs. Lower car after done. Drain coolant.
2. Remove intake shroud. 4 plastic expanding rivets. (Figure B) Note: newer cars only have 3.
Note: On Automatic Transmission cars, you need to remove the clutch fan at this point to be able to remove the radiator fan. This is not shown since I don't have an automatic. You need special tools for this section.
4. Remove the 2 hoses from from the thermostat and the wiring harness. Pull hose clips out on upper and lower hoses. Clip does not come out completely. (Figure G) Pry metal clip off the wiring harness and remove harness from thermostat. (Figure H)
5. Remove bolts from the thermostat. 13mm bolt and 11mm nut on the engine hoist bracket. (3) 10mm bolts on the thermostat.(Figure I) Pull thermostat out.
6. Clean surface of the the engine block (Figure J) and install new thermostat.
7. Reconnect everything in reverse order
8. Refill coolant and bleed system.
a. Open bleed screw and remove cap from expansion tank (Figure K)
b. Turn on car to position B. (engine is off, but cabin fan turns on).
c. Set cabin temperature to highest temp. Set cabin fan to low.
d. Slowly refill coolant until coolant starts to spill out from bleed screw. Your cooling system shouild be air free.
e. Close bleed screw and the put cap back on the expansion tank
f. Turn on engine and make sure there are no coolant leaks. After the engine has cooled, re-check coolant level. Do not open expansion tank cap when engine is hot.