What Is Car Engine Coolant? Everything You Need to Know


As the source of power for cars, engines get extremely hot. Without proper protection, an engine can wear down and even melt, which can cost thousands of dollars to replace.

Car coolant, also known as antifreeze coolant, protects engines from overheating. Coolant also lubricates the moving parts it comes into contact with, which protects damage to the water pump, head gasket, the cylinder and piston timing.

Omar Ramirez, Universal Technical Institute’s (UTI) Education and Development, Curriculum Content Developer, talks about types of car coolant and what happens if you run out of coolant. Omar learned about car coolant as a UTI student himself. Now he’s helping current students master the details of this essential auto component.

What Does Engine Coolant Do?

Wondering what is car coolant exactly? Coolant transfers heat and adds antifreeze protection to an engine, so your car can stay running in optimal condition.

Internal combustion engines create energy by burning fuel. Part of this energy is harnessed by the engine and is used to move the vehicle forward. The remaining energy is converted into heat.

A portion of this heat leaves the engine through the exhaust. The rest remains in the engine block itself.

Average combustion temperatures are close to 2,000°F and, in some instances, may reach as high as 4,500°F. Aluminum components melt at about 1,225°F.

A considerable amount of engine failures are related in some way to engine cooling problems. To protect the engine and to keep it running at the ideal temperature, engine coolant is used.

How Does Engine Coolant Work?

Car coolant is located in a reservoir affixed to the radiator before it’s introduced to the engine block and its components.

Engine coolant is used in conjunction with a liquid cooling system. The liquid cooling system is made up of several components.

  • The water pump, or coolant pump, circulates coolant throughout the system.
  • The radiator conducts heat away from the coolant.
  • Radiator hoses connect the parts of the cooling system.
  • The fan pulls air through the radiator when the vehicle is not moving fast enough to move the air.
  • The thermostat controls the temperature of the coolant.

When the engine’s running, the coolant continuously circulates through the engine and back through the radiator. Coolant exits from the bottom of the radiator after it’s cooled. It’s then drawn into the water pump, which pumps it into the engine’s block and head, where it absorbs the excess heat to control the engine temperature. The coolant is then returned to the top of the radiator where it’s cooled again.

What is Car Coolant Made Of?

All automotive coolants are glycol-based. Common coolants consist of a mixture of ethylene glycol with additive packages and some water.

Another glycol-based coolant consists of propylene glycol and water. The major difference between the two types is that propylene glycol is less toxic.

Pure water has more heat-carrying ability than pure ethylene glycol, so water would be the best coolant to use if the only consideration in the selection of coolant was its ability to carry off heat.

But water presents other challenges. It forms rust on iron engine parts. The rust is then carried off to other cooling areas. The resulting corrosion interferes with heat transfer even before the build-up plugs the radiator and fills the cooling system with sediment.

Coolant helps reduce corrosion and engine rust. Coolant also provides resistance to freezing. It won’t freeze and expand in hyper-cool temperatures like water would. That protects your engine from cracking and experiencing increased pressure.

Three types of coolant are routinely used to service vehicles cooling systems.

Inorganic Acid Technology Coolant

Inorganic acid technology (IAT) coolant is the conventional coolant that was used on older vehicles for many years. This type of coolant needs to be changed more frequently because it tends to lose its qualities faster. This coolant can come in either a green or yellow color.

Organic Acid Technology Coolant

There are several brands of organic acid technology (OAT) coolant. They are available in several different colors, ranging from dark green and orange, to pink and blue.

Hybrid Organic Acid Technology Coolant

Hybrid organic acid technology (HOAT) coolant is a hybrid of IAT and OAT coolants. HOAT is a popular coolant used in a majority of new vehicles.

Always refer to the manufacturer’s specifications in the owner’s manual of your vehicle to verify what type of coolant your vehicle requires. Choosing the wrong product can result in poor performance or engine failure.

How Often Should You Change Engine Coolant?

That depends on your vehicle. As with all other fluids that an engine requires to provide reliable service, coolant or antifreeze needs to be maintained and changed based on the manufacturer’s recommendations. Depending on your vehicle, you may need a coolant designed for high-mileage cars, one that’s formulated for specific manufacturers or one with specialized additives.

Generally, the coolant system should be flushed and changed at least every 50,000 miles. Some newer models may require coolant servicing at every 10,000 miles.

It’s important to drain out the coolant and refill the system, because the process removes rust particles and dirt that can clog up the cooling system. If you notice the coolant has foreign objects floating in it or looks rusty or colorless, it should be flushed and refilled.

The correct type and mixture of coolant should provide protection to:

  • Prevent the coolant from freezing in cold temperatures
  • Prevent the coolant from boiling in hot temperatures
  • Prevent corrosion and rust of metal parts in the cooling circuit and engine
  • Prevent wear of non-metallic elastomers, like rubber and plastic parts
  • Prevent electrolysis, which is corrosion caused when coolant breaks down and becomes electrically charged
  • The wrong coolant can lead to component damage and corrosion, which can negatively impact a vehicle long-term. The effects are sometimes latent, meaning it can be a year before plugging, deposits and corrosion damage causes a problem.

    A malfunctioning coolant system can cause a radiator to be badly corroded or full of plugging internal deposits. People might think a radiator failed, when really the incorrect coolant was used.

    Master Car Coolant in the UTI Automotive Technician Program

    Car coolant is one of the subjects covered in the Automotive Engines Service & Repair course in UTI's Automotive mechanic program. Students of all skill levels in the program learn the knowledge they need to become an entry-level auto technician for a variety of employers.1

    “The UTI program affords many opportunities for an aspiring technician,” Omar says. “The tools, knowledge and experience needed to be successful in any facet of the automotive or diesel industry are present and available at any of the UTI campuses.”

    Contact UTI for automotive school information online or call (800) 834-7308 to talk with a representative.

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    1 ) UTI is an educational institution and cannot guarantee employment or salary.
    2 ) For program outcome information and other disclosures, visit www.uti.edu/disclosures.

    Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


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