Let your engine idle briefly. Anything more simply wastes fuel, increases engine wear, and increases emissions. With computer-controlled fuel injection engines, you need to idle only a few minutes on winter days. When it’s below -20°C, plug in the block heater for two hours. Timers are great for this. The block heater will help to warm the engine block and lubricants. In temperatures below 0°C, block heaters can improve overall fuel economy by at least 10%.