Types of Coolant and Antifreeze

Today's coolant market is confusing. In days past all coolant was the green ethylene glycol variety, but not anymore. Now it seems that every car manufacturer has at least one color of coolant.

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What Type of Antifreeze Should I Use?

All Makes and Models
Extended Life 150,000 Miles
Green, Red, Yellow, Orange, Pink, Blue

There are a lot of coolant types to choose from when you go to a well stocked auto parts store, so which one works best in your car? The simple answer is, well, simple: use what came in your car. However, sometimes it may be difficult to decipher what the original equipment manufacturer (OEM) used, especially if you purchased your car used.

In the spirit of trying to keep this often times confusing subject simple, we will review the three basic types of automotive coolant: Inorganic Acid Technology (IAT), Organic Acid Technology (OAT), and Hybrid Organic Acid Technology (HOAT).

IAT coolants are the "traditional green" variety used in virtually all American vehicles from the late 1920s to the mid to late 1990s. Like all antifreeze, it is naturally clear; its color comes from dye. Unlike the other types of antifreeze, it uses silicate and phosphate corrosion inhibitors to protect the metal parts of the engine and cooling system. However, these inhibitors wear out quickly, so IAT type coolants need to be flushed every two years or 30,000 miles.

OAT coolants typically do not use silicate and phosphate corrosion inhibitors. Different manufacturers use different chemical additives to battle rust and corrosion, and they all dye their coolants different colors. GM's ubiquitous DEX-COOL coolant is an OAT antifreeze dyed orange. Toyota, Volkswagen, and Audi all use their own formulas that happen to be dyed pink. Honda uses a dark green dye. OAT coolants have longer service lives than IAT coolants, needing to be flushed every 5 years or 150,000 miles.

HOAT coolants use different additives than OAT, but also use some silicate to protect aluminum surfaces. Modern Ford, Chrysler, and most European vehicles use their own HOAT coolant formulas. Ford's is dyed yellow and Chrysler's is orange (not to be confused with DEX-COOL). Both use the marketing name of GO-5. HOAT coolant has the same service interval as OAT (5 years or 150,000 miles).

Review the chart below for a quick guide to coolant types.

Summary

• IAT - Used in early to mid-late 90's Domestic vehicles
  
• OAT - Used in late 90's GM and most Asian vehicles
  
• HOAT - Used in 2000's Fords, Chryslers, and most European vehicles
  

Coolant Cocktails?
Although you can mix coolant types without harm, it is highly recommended against. If you mix an OAT or HOAT with an IAT, you will lose the extended service life of the OAT or HOAT coolant. Some people say that if you mix these types of coolant it can result in the coolant gelling, but if you keep your cooling system well maintained, this should not be a problem. In general, do not make coolant cocktails!

And finally, what about the "Universal, All Makes, All Models" coolant you see stuffing store shelves? Basically, those are OAT DEX-COOL clones. I would personally steer well clear of them unless your vehicle is designed for OAT coolant.

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Relevant Sites
Here are some external links to sites with information relevant to this article.

One of the Best Articles I Could Find About Coolant
Valvoline's Zerex Product Guide (PDF-2.25MB)

Automotive Home Outdoors Tool Talk Miscellany