What Does an Engine Block Heater Do?

An engine block heater is useful to car owners living in really cold climates. The first time a driver starts a car on a cold morning is when lots of engine damage can happen. To prevent that, it warms the engines oil or coolant to make starting easier and prevent start-up damage.

Do You Need an Engine Block Heater?

When to Use an Engine Block Heater

When temperatures are below -15 degrees Celsius, engine oil becomes thick. Thick, cold oil makes the engines starter work harder, causing long cranking times that can quickly deplete the battery, especially if your battery is old. An engine has small passages that allow the oil to lubricate critical parts. Cold oil does not flow into the small passages, allowing metal parts to rub against each other.

engine block heater cable
An electrical cord near the vehicle’s grill is a sure sign the car has an engine block heater.

Drivers living and driving in cold climates that have noticed their cars being more difficult to start on really cold mornings may want to consider buying and installing an engine block heater. Older, higher-mileage vehicles and trucks with large, low-compression engines can reduce start-up damage and improve start-up emissions too.

Is an Engine Block Heater Worth It?

Cold temperatures can cause different metals in your engine to become tighter. Tighter clearances mean more friction. Some engine builders state that as much as 75% of the damage done to an engine happens at start-up. Metals also become more brittle when cold, so the chance a worn part may break is greater when it is cold. Your car’s electrical system is even impacted by cold temperatures.

Damaged Crankshaft
When you start your engine, the oil pressure is low. In extreme cold, the oil may not lubricate critical bearings and can cause scoring and damage to difficult to replace parts, such as this crankshaft.

Car batteries are less efficient when cold and can easily become discharged trying to start a freezing cold engine. Whether a block heater is worth it depends largely on where a driver lives and the climate they drive their vehicle in. It is a good idea to equip your car with one if you frequently need to drive your car or truck when it is very cold.

Dead Battery jump start
Cold temperatures make starting a car more difficult for the electrical system. An engine block heater can prevent you from needing to get a jump start.

Engine block heaters that warm the engine coolant are effective at improving the warm-up of the car or trucks heater. It can also be useful for drivers that want the inside of their car to warm up quicker than usual. A block heater used with a remote starting system can be an excellent option for drivers living in cold climates.

How Long to Leave an Engine Block Heater Turned On

car covered in snow
Turning on an engine block heater four hours before you need to drive will prevent cold oil and coolant from damaging your engine. 

Most people will plug their block heater in when they go to bed. Research has demonstrated that a block heater is only effective at raising temperatures for about four hours. After that, the increase in temperature is a lot less significant.

A neat trick is to pair your block heater with a timer to control when it’s on and when it’s not. These timers prevent wasting electricity by only turning it on a few hours before the driver needs the car.

What Types of Engine Block Heaters Are There?

Automobile manufacturers that build specialty vehicles intended for use in the extreme cold often equip their vehicles with OEM models installed straight from the factory. However, most cars and trucks owners will need to install an aftermarket block heater.

The types of block heaters available are:

  • Oil Pan Heater – These attach with magnets to the engine oil pan and heat the oil, but not the engine coolant.
  • Engine Warming Blanket – These are like an electric blanket and are usually draped or wrapped around the engine when in use.
  • Inline Coolant Heater – These can be installed in the lower radiator hose or in a heater hose and work by heating and circulating coolant.
  • Freeze Plug Heater – When most people refer to a block heater, this is the device they are referencing. These replace a freeze plug with a heating element. A 120V AC plug hanging from the grill of the vehicle is a dead give-away that the vehicle is equipped with one.
  • Bolt-on Heater – On some vehicles, one of the cylinder head bolts can be replaced with a hollow shaft that houses an electric heating element. These are more common in industrial equipment and vintage vehicles.

What is the Best Type of Block Heater?

The best type of engine heater depends on a number of factors. Drivers that know they will need a block heater every day during the winter should invest in a freeze plug heater, and should also have a magnetic oil pan heater as a backup for those really brutal cold days.

snowplow in blizzard
Drivers of snowplows and other winter equipment often install engine block heaters to keep their vehicles reliable.

Inline coolant heaters are most useful for drivers who live in regions where oil is likely to remain viscous, but freezing temperatures may cause water in the engine to freeze. These are particularly effective for getting a car’s heater producing warm air faster.

An engine warming blanket is most useful for drivers that do not regularly encounter below-freezing conditions but may a few times a year. These are the simplest form of engine block heaters but are also the least efficient ones.

How do You Install an Engine Block Heater?

The most common and efficient heaters are those that heat the coolant.  Installing these heaters is not difficult for most average DIYers. Block heaters that install in the lower radiator hose or in one of the engine freeze plugs will require the installer to drain the vehicle’s coolant and refill it afterward. This is also a good time to make sure the mixture of your coolant is correct to prevent freezing the water in your engine.

Oil pan mounted heaters are super simple to install. Users attach the heater to the oil pan with magnets and plug it into the wall socket. Similarly, you plug in an engine blanket and drape or wrap it around the engine.

An Engine Block Heater Might Be Right For You When…

  • You live in a climate that gets below -15 degrees Celsius.
  • You drive a tractor or truck that uses a very large, low-compression engine.
  • Your car or truck struggles to start in the snow.
  • You want to use your heater sooner in the morning.

Do you have an engine block heater ready for your car and the winter months? Let us know your experience and what type you prefer in the comments section below!


About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

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    Absolutely loved this Engine block heater article. Thank you so much for sharing this valuable information.

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