Sorry if this has already come up in this thread, but:
BMW has been experimenting with fully encapsulating the engine with insulating materials to preserve heat to minimize the number of truly "cold" starts:
Quote:
To keep temperatures within the engine compartment at a high level for as long as possible and to avoid having to warm up the engine from the regular ambient temperature, the engine is fully encapsulated. In addition to the air flaps behind the BMW kidney grille already introduced in 2007 in the context of BMW EfficientDynamics, an engine on a prototype that is already developed is completely surrounded by fully clad walls and panels, the engineers using proven materials from the underfloor of the car for insulation purposes.
With encapsulation, an engine running at a temperature of 80 °C or 176 °F cools down much more slowly after being switched off and still has a temperature of approximately 40 °C or 104 °F after 12 hours.
With each degree of temperature having a significant influence on fuel consumption, this improvement alone provided by encapsulation reduces fuel consumption by up to 0.2% for each extra degree of temperature (in °C).
This method of maintaining temperatures is equally suited for all kinds of vehicles and in all climate zones, although it is somewhat more effective at low temperatures. Highly efficient dampening of heat on the drivetrain also has some positive side effects.
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Source:
Green Car Congress: BMW Outlines Intelligent Heat Management Applications for Reducing Fuel Consumption and CO2; New Thermoelectric Generator Unit Integrated with EGR