Engine block heaters assure the engine is warm enough to start. Diesel fuel is harder to start in cold weather, therefore engine block heaters are helpful in colder regions.
In addition to assuring that the engine starts during colder weather, engine block heaters can also help warm the car up faster. There are typically three different types of engine warmers. First, the block heater is designed to keep the engine block heated. These are electric powered and use an electric chord to plug directly into a three-prong 110-volt electric socket. Second are battery warmers. Cold weather can decrease a battery's power. There are two choices for this: a hot plate warmer or a battery blanket. Both require being plugged into a nearby 110-volt electric socket. Third are oil warmers. This is an electric dipstick that plugs into a 110-volt electric socket. It replaces the normal dipstick and keep the oil in the crank case warm.