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Understanding Antifreeze: What’s Best for Your Car or Truck?


Antifreeze is a bit like engine oil: every vehicle needs it, but not necessarily the same kind. Fortunately, there aren’t nearly as many types of coolant out there to choose from as there is oil, but it’s still important to understand the differences between each kind and know how to make the right decision when it comes to buying antifreeze for your car or truck.

Don’t Just Color Match

It can be tempting to pop the cap on your radiator’s overflow tank (never when it’s hot), look at the color of the coolant you already have in the car and then buy whatever antifreeze matches that shade. Unfortunately, you can’t simply use color as a shorthand for the right coolant for your car.

Ultimately, your owner’s manual will recommend a specific type of antifreeze to use, but while some brands are adamant about you buying it directly from the dealership, others will leave it more open-ended by simply specifying a class or type of coolant that’s compatible with your vehicle’s engine.

The Three Main Types

The color of your antifreeze typically lines up with these three options:

1. Inorganic Acid Technology (IAT): Green, sometimes yellow

2. Organic Acid Technology (OAT): Orange

3. Hybrid (HOAT): Hybrid coolant combines both types together and bundles in nitrites as well. The dyes are added by manufacturers to try to align each type of coolant in the right category, unfortunately there’s no rigid set of rules guiding this process, so always read the label.

What Makes Them Different?

Prestone pre-mixed antifreeze

IAT is composed primarily of phosphates that work best to protect iron engine blocks from corrosion and silicates that are more in tune with preserving aluminum cylinder heads, radiators and water pumps. OAT coolant moves to a different two-chemical formula that’s designed to last much longer than IAT, allowing you to go longer between changes and also works better when mixed with harder water.

If OAT lasts longer, then why doesn’t every company use it? While it does tend to resist breakdown well, it’s not quite as good at protecting any metal that might become exposed inside an engine. This is why some companies created HOAT, using additives that combine the properties of both organic and inorganic coolant.

Can I Mix Them?

Mixing IAT and OAT coolant together is asking for trouble. Not only do you risk diluting the protective properties of IAT if it’s combined with other types of coolant, but you can actually increase the risk of corrosion as a result. Even if you drain everything out of a system that was designed for one type of coolant and replace it with another, you’ll still have residue left inside the motor’s cooling channels that can cause problems when mixed with the new coolant.

The bottom line: Read your manual, understand the coolant you need and then make sure to match it with what you choose at the store.

Check out all the chemical products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on antifreeze, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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