This is the heater that I referenced in post 7.

BMW NA won't sell the product. It may have something to do with their perception of the consumer risk. Having said that, the original manufacturer of the system that BMW sells in Europe is Webasto, and they make some good products. I have used them on commerical heavy duty engines, and seen them on Class 8 highway trucks, but have never installed one on a car.

Webasto has a US subsidiary, and a US dealer network. The heater is available in diesel or gasoline versions. They call it BlueHeat. You can retro fit it, although I haven't checked whether they have a kit for your specific model. It may also be tough to find the gasoline model, as the diesel model is most popular. You can also get the timer and the remote control that BMW supplies with it in Europe, directly from Webasto. Have a look at it here.

http://www.webasto.us/am/en/am_auto_heaters.html

Good luck.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue