What Is Antifreeze and What Is It Used For?

NASCAR gets away with running just water in their cooling systems, so why do you and I have to use antifreeze? If it’s called “antifreeze,” implying cold weather driving, then why do we also call it “coolant”? And why is antifreeze sweet? Just what is antifreeze anyway? Here are the answers to everything you probably ever wanted to know about the benefits of antifreeze.

What is antifreeze?

Antifreeze is a liquid that circulates in the cooling system primarily as a heat exchanger between the engine (picking up heat) and the radiator (shedding heat). This lets the engine run at the optimum temperature for performance, efficiency, longevity and emissions. While primarily acting as coolant, it’s also an “anti-freeze” liquid, preventing the cooling system from freezing solid in cold weather.

You’ve seen jugs of antifreeze at the auto parts store, or even the grocery store. Widely available and affordable, this critical fluid isn’t changed out nearly as often as oil, and there have been many changes to the stuff over the years, leaving many drivers unfamiliar with antifreeze.

What is antifreeze used for?

Automotive antifreeze has three primary uses: It lowers the freezing temperature, raises the fluid’s boiling point and prevents corrosion.

Prevents freezing

The primary ingredients in antifreeze prevent the formation of ice crystals, lowering the freezing point of the liquid to a chilly minus 34 degrees Fahrenheit. This refusal to freeze prevents engine damage in extremely cold weather, circulating fluids through the engine and cooling system as it warms up.

Cooling properties

Antifreeze is often called “coolant,” since it circulates in the cooling system and subcomponents like the water pump, radiator and thermostat. It cools the engine by raising the boiling point of the fluid to approximately the operating temperature of the engine and then drawing away the excess heat. These cooling properties combined with the pressurized system prevent the antifreeze from boiling off, and it remains a liquid.

Prevents corrosion

Fluids plus metal is a recipe for rust, especially when you add heat. Antifreeze additives prevent rust and corrosion, enabling longer engine life. Antifreeze’s ability to prevent internal corrosion is one of the many reasons engines last longer than ever.

What is antifreeze made of?

There are a few different ingredients depending on the age, brand and type of antifreeze.

Water: Despite all the warnings against using straight water, your cooling system will operate best at 50% water and 50% antifreeze. If you buy a pre-diluted antifreeze mix, you’re buying a good amount of water.

Ethylene glycol: This is the primary ingredient in modern antifreeze. It’s a compound that prevents ice crystal formation in water, dramatically lowering the freezing temperature. It’s literally anti-freeze. This is also where the sweet smell and taste come from.

Glycerol: This was the original antifreeze that ran in cars 100+ years ago. Also called “glycerin,” this compound gives antifreeze its viscosity. Oddly, it also has a sweet taste.

Propylene glycol: This is a new main ingredient in antifreeze, a synthetic organic compound that is odorless, colorless, nontoxic and less dangerous than ethylene glycol.

Additives: Additional ingredients such as phosphate and sodium benzoate prevent corrosion and keep the pH in balance.

What color is antifreeze?

Ask any four of your friends what color is antifreeze, and you’ll likely get four different answers. Your friends aren’t necessarily wrong, as antifreeze can be any number of colors, and before you ask—no, these aren’t different flavors.

Green

The most common color of antifreeze over several decades, this stuff is still on the shelves and in radiators today. Today, it’s called “conventional” or “inorganic” antifreeze.

Orange

What antifreeze is orange? It’s called “Dex-Cool.” This is the newer stuff, filling cooling systems starting in the 1990s. Whether your vehicle comes with green or orange antifreeze, keep buying that color. And just remember, you cannot mix the colors or you’ll have a serious and expensive engine problem.

Blue

European cars often have a blue antifreeze mix, though you can find it in American vehicles as well. This could be a “hybrid” antifreeze, combining inorganic and organic antifreeze.

How do I check my antifreeze?

Unlike engine oil, your engine’s antifreeze doesn’t have a handy dipstick. However, there are a few ways to check your antifreeze and keep everything at the right temperatures.

Look at the overflow tank

It should be above the “hot” and “cold” lines when the engine is respectively warmed up or cold. If it is low, you can add more. The premixed antifreeze just requires you to pour it into the overflow tank or radiator, while undiluted antifreeze needs you to mix it 50/50 with distilled water.

Check your owner’s manual

That book in your glove compartment that many ignore offers a bunch of advice. Under the maintenance section, it has a recommendation for changing your antifreeze. Most recommend changing fluid at 60,000 miles or more, with some even suggesting 150,000 miles. Keep it changed on schedule and you won’t have to worry about it.

Antifreeze testing

If you really want to check the condition of your antifreeze, grab a cheap coolant tester, available for less than $5 from any auto parts store. Simply unscrew the radiator cap, drop in the tester’s inlet hose, and draw up a small amount of coolant. The arrow will display the antifreeze’s boil-over and freeze-protection levels.

Have a feel

Dip a finger into the radiator or coolant overflow tank (please, only when the engine is completely cool). Antifreeze should feel slick and smooth, not gritty. Grit suggests contaminants, meaning you need a fluid change ASAP.