Car Block Heater: Unsung Hero of the Frozen North

block heater plugged in
Electrical plug-ins are often provided for block heaters in areas where it gets especially cold. Reino Hanninen / Age Fotostock / GettyImages

Car block heaters are pretty much unheard of in sunnier climes. Even if you live in an area where block heaters are ubiquitous, they aren't exactly exciting. Block heaters are very much an out of sight out of mind type of technology. In most cases you wouldn’t ever know a car had one installed without seeing the telltale electrical plug hanging through the grill. But as the mercury begins to plunge each year, it becomes clear why block heaters are the unsung heroes of the frozen north.

What are Block Heaters?

Block heaters are engine-heating devices that are designed to warm up an engine, and the relevant fluids, prior to starting it. Depending on exactly how cold the surrounding environment is, this can accomplish a number of useful tasks. The main purpose is to make it easier to start the engine, but preheating the engine oil, antifreeze, and internal engine components also reduces wear and tear, reduces emissions, and makes for a more comfortable environment inside the vehicle by allowing the heater to blow hot sooner. In the coldest of environments, where the temperatures dip below the freezing point of the water/antifreeze mixture in an engine, block heaters can also keep the engine coolant liquid overnight and prevent catastrophic engine damage.

Types of Block Heaters and Engine Heaters

There are a handful of different types of block heaters, but they all rely on the same basic technology (some type of heating element) and work via the same basic mechanism (heating up some part of the engine.) The most common types of block heaters include:

  • Freeze plug heaters
    • Installed in place of a freeze plug in the engine block.
    • Heats the coolant directly.
    • Not transferable between vehicles.
  • Dipstick heaters
    • Installed in place of the oil dipstick.
    • Heats the oil directly.
  • Engine-warming blankets
    • Installed on top of the engine or attached to the inside of the hood.
    • Works like an electric blanket.
  • Oil pan heaters
    • Bolted onto the oil pan or attached via magnets.
    • Heats the oil indirectly by heating the pan.
  • In-line coolant heaters
    • Installed in-line with a radiator hose.
    • Heats the engine coolant directly.
    • Circulating versions include a pump that cycles warm coolant through the engine.
    • Non-circulating versions are less complex but also less effective.
  • Bolt-on block heaters
    • Bolted to the exterior of the engine.
    • Heats the engine through direct contact.
    • Indirectly heats the engine coolant.

Installing and Using a Block Heater

Some block heaters are easy to install and move from one vehicle to another, like blanket style heaters and the ones that are designed to replace your dipstick. In fact, installing a dipstick heater is no more difficult than checking your oil. Others are relatively easy to install, like in-line coolant heaters, while traditional freeze plug block heaters are best left to the professionals. In any case, if you do decide to install your own block heater, it’s important to remember that the one common element is that every block heater comes with an electrical cord that has to be safely routed through the engine compartment. If the cord strays too close to moving components like pulleys or belts, it can become damaged.

If that happens, your block heater fail to work, or even short out, the next time you plug it in.

The best way to use a block heater depends on the temperatures that you’re dealing with. If you live in an area where it gets cold enough to freeze your antifreeze and crack your block, then you’ll want to plug your block heater in whenever you leave your car parked for any amount of time. It should always be plugged in overnight in those circumstances, but if you find yourself parking in an area where power outlets are provided for block heaters, plugging in will result in easier starts, and less wear and tear on your engine, even when you aren’t parking overnight.

In situations where it doesn’t get cold enough to crack your block, you can usually save some money on electricity by using a timer. By setting the timer to kick your block heater on a few hours before your commute each morning, you’ll avoid wasting electricity overnight, but you’ll still see the benefits of an easier start, less wear on the engine, and hot air from your vents much sooner.