Engine coolant, also called antifreeze, is available in a multitude of colors, including green and orange. While green coolant is often thought of as traditional or conventional and the color orange is associated with the newer long-life products, there are no hard-and-fast color rules when it comes to engine coolants. All will help keep the cooling system from both overheating and freezing. The difference is found in the technology each one utilizes to protect the cooling system’s components from corrosion.
Inorganic Additive Technology
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This technology is used in the conventional green coolant. Silicates and phosphates added to a base of ethylene glycol protect the metals in the cooling systems from corrosion. This type of coolant is used primarily in cars built before 2000 with steel and copper components. Some IAT coolant formulations use propylene glycol in place of the ethylene glycol because, although it is similar chemically, it is less toxic to humans, pets and the environment. Every two to three years or 30,000 miles, the anti-corrosion additives in green coolant are depleted and the coolant needs replacing.
Organic Acid Technologies
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During the 1990s, cooling system components shifted to more aluminum and nylon, so coolant was reformulated to protect these new materials. This type of coolant uses organic acids to prevent corrosion and is usually orange in color. A third type of coolant utilizes Hybrid Organic Acid Technology that combines the benefits of IAT and OAT into one product. HOAT coolants are often yellow or orange but may also be blue, red or pink. Both of these types are long-life coolants and may last up to five years or 150,000 miles before they need to be replaced.
Coolant vs. Water
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While water can act as an effective engine coolant all by itself, it has some limitations, including a freezing point of 32 degrees and a boiling point of 212. But coolants usually contain a mixture that is half water and half either ethylene glycol or propylene glycol, which extends the functional temperature range of the cooling system even further, from somewhere around minus 30 degrees to as high as 265.
Mixing Coolants
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Mixing two types of coolants is not dangerous — causing explosions or other pyrotechnics — but a mixture may damage the cooling system’s components because OAT coolants are designed to protect different materials than IAT coolants. An additional consideration when using two coolant types is that the resulting mixture will last only as long as the coolant with the shortest lifespan. So a mixture of a long-life HOAT product with a conventional green coolant will still be depleted after three years or 30,000 miles.