The Webasto Tandem 717 consists of the Air Top 2000 in-cab heater, and the TSL 17 engine preheater. Webasto Air Top 2000 eliminate idling for heat, saves on fuel costs, and runs up to 20-hours on a single gallon of fuel. Webasto TSL 17 preheats the engine's coolant, eliminating cold starts which reduces wear ' tear.