For those of you with a TIS...
The TIS instructions for removing the thermostat are incorrect for at least some VINs, and assume the engine has a belt-driven fan rather than an electric fan. (Bentley fans will be gratified to know that the Bentley book has it right. I should have used mine!)
While it is (just barely) possible to remove the thermostat with the fan and shroud in place the job will go much faster and will be much easier (trust me on this) if you remove them first. Take out the four plastic locking rivets that secure the intake piece over the fan shroud by pulling out their center pieces. Then there is a Torx bolt on the right side and a plastic locking rivet on the left of the fan shroud. Remove the bolt, pull the center piece out of the rivet and remove it, disconnect the two connectors on the right, and pull the fan shroud straight up and out. This will make doing the thermostat very easy.
To remove the thermostat itself unclip and remove the electrical connector and hoses, take out the four bolts, and pull it straight forward. Torque the replacement to 10NM.
You'll need approximately 2 quarts of coolant if you mix it 60/40. Don't forget to bleed the system.
In the lucky-for-once department, remember all those bad E46 thermostats in the 2000-2001 timeframe? I bought a new part number spare back then and two gallons of BMW coolant, based on the certainty that it would fail on a weekend when I needed the car right after the warranty expired. Defying all probability, the one in my car never failed...my new car came with the new part number...and the thing sat on my shelf all this time. Yesterday the one on my wife's car failed at about 80K miles, and I finally got to use it! What are the chances...? (80K...hmmm...think I'll buy another spare for my car, which is fast approaching 50K miles.)
Though I did not write it down and don't remember it, OBD-II code was straightforward (something like "coolant does not reach regulated temperature") and the thermostat failed by opening prematurely. The temperature gauge showed low, and the engine never got over 160F.
With the new thermostat, the temperature varied from 178F to 208F as it was mapped for varying load conditions. Those of you who whine about the computer-controlled temperature gauge, take note! If it were a simple gauge, the 30-degree temperature excursions that are normal would make it difficult for most people to interpret. BMW definitely got this one right.
JRE