Choosing the Right Coolant for Your Car or Truck

Three people standing by an overheating car on the side of the road with the hood raised and a lot of steam coming from the engine.

Engine coolant, also called "anti-freeze," has three simple purposes:

To cool the engine by removing heat from the metal surfaces and discharging it through the radiator.
To prevent the water, which is up to half the mixed coolant's volume, from freezing in cold weather and damaging the engine.
To help prevent corrosion in the cooling system.

Despite the simplicity of its purposes, choosing the right ant-freeze is, in some ways, harder than choosing the right motor oil. The different types of engine coolants are more different from each other and less compatible with each other.

Using the wrong coolant, or mixing certain types of coolants together, may gunk up the engine's cooling system, which can lead to serious engine damage and void the engine's warranty. If you're not sure which coolant to use, then contact the car's manufacturer.

Coolant Concentration

When buying a coolant, it's important to note the coolant's concentration.

Some coolants come pre-mixed with 50 percent distilled water and should not be diluted prior to use. Other coolants are 100 percent coolant and must be diluted with distilled water, usually to a concentration of 50 percent except in cold climates (where you may want to use a 65 or 70 percent coolant-to-water ratio, but never more than that).

The "more is better" school of thought doesn't apply to anti-freeze. Water is a much more efficient cooler than glycol. Using too low a ratio of water to coolant will reduce the coolant's cooling efficiency and may cause overheating. But using too little coolant to water will make the coolant more likely to freeze and will reduce corrosion protection. For most people in most climates, a 50:50 mix of coolant and distilled water is the sweet spot.

Easy Ways to Choose the Right Coolant

The easiest way to choose the right coolant for your car is to buy it from a dealership that sells that make of car. Or you can just have them change the coolant for you if you prefer.

If you live far from a dealership, you can check your car's owner's manual to see if there are particular coolants that are approved or recommended for the vehicle. If you're lucky, the correct coolant for your car may be expressed as a particular brand name and product, or by a code such as an ASTM code, G code, or JIS code.

If you're not so lucky, the manual will specify a particular type of coolant. The rest of this page will talk about the different types of coolants and how to know which is the right one for your car.

Types of Engine Coolants

If your vehicle's manual specifies a type of coolant rather than a particular product or a standard like ASTM or JIS, then the following descriptions will give you starting points for choosing the correct coolant. Please note that the colors and change intervals are typical, not gospel. Consult your vehicle's owner's manual or service manual for authoritative specifications.

IAT (Inorganic Additive Technology)

IAT coolants are usually green in color and use ethylene glycol as the coolant base. They typically (but not always) use silicates and phosphates for corrosion protection. The usual change interval is two years or 24,000 miles (about 39,000 kilometers). These coolants are used mainly in older vehicles.

Zerex Original Green or Peak OET are examples of IAT coolants.

OAT (Organic Acid Technology)

OAT coolants are usually orange or dark green in color. They use propylene glycol as the coolant base and organic corrosion inhibitors such as carboxylates or triazole. The usual change interval is five years or 50,000 miles (about 80,000 kilometers).

ACDelco Dex-Cool and Zerex Dex-Cool are common examples of OAT coolants.

HOAT (Hybrid Organic Acid Technology)

First of all, the word "hybrid" in HOAT has absolutely nothing to do with hybrid cars. Walk away from anyone who tells you that it does.

HOAT coolants are usually yellow, but can also be orange, purple, or pink. They are glycol-based and contain both organic and inorganic corrosion inhibitors. The change interval can range from five to ten years, or 50,000 to a whopping 180,000 miles (about 80,000 to 290,000 kilometers).

Zerex G-05 is a widely-used example of a HOAT coolant.

HOAT Phosphate-Free / NAPS-Free

This is a glycol-based HOAT formulation that contains no nitrites, amines, phosphates, or silicates (NAPS). It usually is turquoise in color and uses organic acids for corrosion resistance. The typical change interval is five years or 50,000 miles(about 80,000 kilometers).

The absence of NAPS is to protect the engine's gaskets and seals. Using the wrong coolant in a car that requires HOAT Phosphate-Free / NAPS-Free coolant most likely will void the warranty.

True aftermarket NAPS-free coolants are hard to find. You're better off buying this one from your dealership.

P-HOAT (Phosphated HOAT)

P-HOAT is usually pink or blue in color, but may also be dark green. It is glycol-based and uses organic acids and phosphates for corrosion resistance. It's most-commonly used in Asian cars such as Toyota, Nissan, Honda, Hyundai, and KIA. A typical change interval is five years or 100,000 miles (about 160,000 kilometers).

PEAK OET Extended Life Green and Valvoline 675130 are two common examples of P-HOAT coolants.

Si-OAT (Silicated HOAT)

Si-OAT is usually purple in color. It's glycol based and uses both organic acids and silicates for corrosion protection; but contains no nitrites, amines, or phosphates It's most-commonly used in late-model German cars. The change interval is usually five years or 150,000 miles (about 240,000 kilometers).

Zerex G-40 is a popular example of an Si-OAT coolant.