How to Replace a BMW Thermostat

Remove the Thermostat
1. Place wooden blocks behind the rear wheels. Jack up the front of the BMW using a floor jack. Use jack stands placed on the reinforced jack slots located an inch in front of each front tire to secure the car. Open the hood and secure it using the safety bar.
2. Turn the key in the ignition to the ''On' position. This will turn on the accessories without starting the engine. Turn the heater onto the highest setting. Let it run for five minutes. Turn the ignition back to the 'Off' position and remove the key.
3. Grab a bucket and slide under the car. Locate the radiator drain plug. It is centered on the bottom of the radiator. Place the bucket directly under the drain plug. Unscrew the drain plug using an adjustable wrench. Allow the fluid to drain. This may take up to 30 minutes. Replace the plug.
4. Look for the rear engine coolant drain plug. This is located near the oil drain pan. It may be difficult to see. On some cars manufactured prior to 1992, it is located between two headers. On other models, it is located near the oxygen sensor. Slide the bucket under this plug. Unscrew the plug until the coolant begins to flow out using either an 8 mm or 10 mm hex socket. This varies depending on the bolt, so try both and pick the one that fits. Allow the coolant to drain completely. This may take up to an hour. Replace the plug.
5. Locate the alternator cooling duct. This is a tube that goes from the alternator to the radiator. Slide it off. There aren't any bolts or fasteners on it, so it should slide off easily. In front of the alternator cooling duct, you will notice six shroud screws. Remove these using a 32 mm wrench.
6. Remove the two hose clamps that are attached to the side of the thermostat housing. This can be found near the radiator on the driver side of the vehicle. Slide the hose up. Beneath the hose you will see the fan. Using the 32 mm wrench, loosen the bolt on the fan. The retaining nut is a backwards threaded nut. As such, you have to loosen it by turning your wrench clockwise. Hold on to the fan as you do this so that it doesn't fall when the bolt is removed. Take the fan out and set it aside.
7. Unbolt the five bolts located around the thermostat housing using the same socket as you used to remove the rear engine drain plug. Lift up on the housing once all of the bolts are removed. You will see the thermostat. On the thermostat, there is an arrow. Take note of the direction of the arrow as you will need the arrow on the new thermostat to point in the same direction. Remove the thermostat. Clean the area from which you removed the thermostat using clean shop towels and a plastic scraping tool if necessary.
Replace the Thermostat
8. Place the new O-ring that is included with the new thermostat onto the hole upon which the new thermostat will be placed. Align the thermostat with the bolt holes ensuring that arrow is pointed in the proper direction. Slide the bolts through the holes and tighten them.
9. Replace the gaskets located around the thermostat housing. Replace the thermostat housing. Ensure that the gaskets are properly positioned as you tighten the bolts that secure the housing. This will help to prevent coolant leaks in the future. You may have to scrape off the old gaskets using the plastic scraping tool.
10. Slide the fan into place and secure it by tightening the bolt counter-clockwise. Replace the hoses you removed and tighten the hose clamps to secure them.
11. Fasten the six shroud screws. Replace the alternator cooling duct.
12. Remove the radiator reservoir cap on the passenger side of the vehicle. Use a funnel to refill the coolant reservoir with BMW coolant to the 'Cold' line. You will notice the fluid level go down. As this happens, add more coolant until the level stays even with the 'Cold' line.
13. Loosen the radiator bleed screw using a Philips screwdriver. This is located beside the reservoir. It has a flat screw with an X on top. Turn the ignition to the 'On' position without starting the car. You will notice that the coolant bubbles up from the bleed screw. As long as it is doing this, you need to check the fluid level and add coolant to the reservoir to keep it at the 'Cold' line. When only fluid comes out of the bleed screw without bubbling, tighten the screw and turn the ignition off.
14. Put the radiator reservoir cap back on and tighten it. Start the car. Allow it to sit idle for five minutes and check for coolant leaks. Clean up your tools and dispose of the coolant as per local laws.