What Is a Block Heater? Definition, Meaning and Concept

A block heater is a device used in vehicles to protect the engine from cold. Typically mounted to the engine block coolant passages, it works much like an electric water heater in a home. When plugged into a household outlet, the block heater heats the coolant inside the engine block; a hot engine starts more easily than a cold engine. Both gasoline and diesel engines can benefit from the installation of this device.

In cold temperatures, the spark plugs in a gasoline engine can become covered with frost. This is due to moisture from an engine running hot and cooling in cold temperatures. Residual moisture from the combustion process is allowed to freeze within the cylinder walls, creating a difficult starting condition. By placing a heater inside the engine coolant passage, the entire engine stays warm, making it easier to start in cold weather.

Another benefit of a block heater is that the engine oil stays fluid and easily pumps throughout the engine when starting. In a cold engine, the oil can remain very thick and unable to pump through the lubrication system for several seconds to several minutes. This creates lubrication problems that greatly reduce the life of critical engine components such as the oil pump, camshaft, lifters, and main bearings.

In a diesel engine, the benefits are basically the same as in a gasoline engine; however, hard starting diesel becomes even more difficult in cold weather. The diesel engine starts by creating heat in the combustion chamber of the engine. On a cold engine, this task is made more difficult as it requires a block heater to aid in the engine's starting ability.

The most common mounting procedure for a block heater is to remove one of the engine freeze plugs and replace it with a heater module. The block heater design allows it to be a direct replacement for a freeze plug. The heating element or block heater coil is placed in the coolant passage of the engine block, and the mounting plug fits snugly into the freeze plug hole. Once in place, the coolant can be refilled, making the heating element completely submerged in the coolant. An electrical cable, complete with plug, is attached to the heating coil and extends to the grill area of ​​the vehicle, where it can be easily accessed and plugged into a power source.