Is Coolant the Same as Antifreeze? Plus Other Related Questions Answered

Your car has many different fluids, one of which is the coolant inside of the cooling system. Many professionals use the terms coolant and antifreeze interchangeably because they mean almost the same thing—almost.

Although it’s generally okay to regard coolant and anti-freeze as one and the same, that view is not entirely correct. Technically, anti-freeze is one of the ingredients that make up the coolant mixture. 

If this seems confusing, don’t worry. Below, we’re going to cover the ins and outs of coolant, including the subtle yet important difference between the terms coolant and antifreeze.

What’s the Difference Between Coolant and Antifreeze?

If you go to purchase a gallon of coolant, there’s a good chance it will say anti-freeze/coolant on the side. Over the years, the automotive industry has adopted the trend of using these two terms interchangeably. But as was mentioned, anti-freeze is, in fact, one of the ingredients that make up the coolant mixture.

To understand this concept better, it’s important to be familiar with the role of coolant in the cooling system. Primarily, coolant is responsible for removing excess heat from the engine and transferring that heat to the atmosphere via the radiator. The coolant mixture must also resist freezing in the winter—and that’s where the anti-freeze portion of the equation comes in.

You see, water does a good job of removing heat from the engine. But in frigid temperatures, water can freeze, potentially leading to engine and cooling system damage.

That’s why coolant is primarily a mixture of water and antifreeze. The antifreeze—either ethylene glycol or propylene glycol—is the part of the coolant mixture that prevents freezing. A coolant mixture that’s approximately 50% water and 50% antifreeze is best for most vehicles under most conditions.

What’s great is that pre-mixed coolant, which contains approximately 50% water and 50% antifreeze, is available for most makes and models. Going the pre-mixed route means that you don’t need to mix the anti-freeze with water—it’s ready to go right out of the bottle.

What is Coolant Exactly?

You now know that coolant is primarily a mixture of water and anti-freeze (ethylene glycol or propylene glycol). But there’s a third ingredient—the additive package—that’s often overlooked.

In reality, coolant isn’t truly 50% water and 50% anti-freeze. Instead, a typical mixture is made up of the following:

• 50% water
• 47% anti-freeze
• 3% additives

Even though the additives (also known as corrosion inhibitors) make up only a small portion of the coolant mixture, they play a big role in protecting the cooling system against rust and corrosion. What’s more, the additives are what differentiate one type of coolant from another.

What are the Different Types of Coolant?

All automotive coolants are the same in that they contain water and anti-freeze. It’s the additive package that distinguishes one type of coolant from another.

There are three primary types of coolant: inorganic acid technology (IAT), organic acid technology (OAT), and hybrid organic acid technology (HOAT). Each is defined by its additive package, which contains a variety of corrosion inhibitors. 

Inorganic acid technology (IAT) coolant

IAT coolant is the traditional green mixture that was used in most vehicles until the late 1990s. This type of coolant contains inorganic salt additives, which can cause deposits to form (when mixed with hard water) and eat away at water pumps. That’s why the formula is no longer used in light-duty production vehicles. Typically, IAT coolant has a service life of two years or 30,000 miles.

Organic acid technology (OAT) coolant

OAT coolant does not contain the inorganic salts sodium silicate and phosphate the way IAT coolant does. Instead, the additive package in an IAT mixture contains organic corrosion inhibitors, such as Sebecate and Benzoate. Usually, OAT coolant has a service life of five years or 150,000 miles.

Hybrid organic acid technology (HOAT) coolant

As you might guess, HOAT coolant combines both inorganic and organic additives, which is why many universal coolants use the formula. Typically, HOAT coolant has a service life of five years or 150,000 miles.

But wait—what does the color of the coolant mean? Unfortunately, the color doesn’t necessarily define the coolant type. Coolant comes in a variety of colors because automakers dye their blends for identification.

What Coolant Does My Car Need?

It’s important to choose the correct type of coolant for your application because vehicle manufacturers tweak their additive packages. For example, Audi’s pink HOAT coolant contains some silicates but is phosphate-free. By comparison, Toyota’s red HOAT coolant contains phosphates but is free of silicates.

Using the wrong type of coolant can cause corrosion and sediment build-up, which can eventually damage the cooling system and engine. That’s why choosing the correct type of coolant is always critical—even when you’re just topping off.

You can determine what kind of coolant your car needs by consulting your owner’s manual or supplemental service booklet.