Thought I would create a little DIY for the N57 thermostat. One of the easier DIYs, (certainly compared to changing springs and dampers which I did the day before).
You can let several (about 5) litres of coolant run all over the floor or try and catch most of it. I cut the top off a 5L plastic container placed it under the thermostat housing and let it run out as I slowly undid the 4 bolts. I couldnt remove the container when it was full so I then syphoned the coolant into another 5L container placed on the floor in front of the car. A towel caught the drips.
1. New thermostat and gasket (note it is NOT symmetrical)
2. Remove 3 screws to release centre air ducting.
3. Unclip and remove angled air ducting.
4. Squeeze the 2 clips and remove the electrical connector to fan.
5. Remove the only screw holding the fan assembly. On the same side note the tab and locating slot about half way down the fan assembly.
6. Below the radiator top hose. Release clip and lift out fan assembly. Note for re-installation, the two tabs on the bottom edge of the fan assembly which locate with 2 slots below the intercooler.
7.Thermostat housing. Screws are not very tight but i dont know the torque settings (anyone ?). The gasket sits in a groove in the plastic housing which also has a hole for the pin on the top of thermostat. All fairly obvious. Tighten up evenly and check for leaks. I returned most of the original clean coolant and topped up with 50% antifreeze made from the concentrated BMW antifreeze. Bleed the cooling system as for BMWs with belt driven non-eletrical water pumps.
Hope that is helpful.