Rick's Free Auto Repair Advice

Coolant types

Coolant types — five most common coolants

The old standby — Green IAT coolant

Inorganic Additive Technology (IAT) coolant

IAT coolant was used for decades. It’s green. It’s comprised of approximately 95 ethylene glycol or polypropylene glycol and an anti-corrosive and water pump lubricant package using silicates, phosphates, borates, nitrites or amines.

The anti-corrosive additive package in IAT coolants was designed to protect cast iron engines, steel heat tubing and copper radiators.

How does IAT coolant work?

The Silicate or phosphate additives deposit on the walls of all the metals in the cooling system to form an Anodic layer of protection. Once the anodic coating layer is higher than any cathodic current in the solution, the system is considered “passivated,” preventing electrolysis. In other words, the anodic coating prevents the transfer of electrons from one metal to another, something we call corrosion.

Downsides to IAT coolant technology:

• Short life — The silicates and phosphates precipitate out of the solution, so they have a short life of less than 30,000 miles or about 2-years.
• Borate as an anodic corrosion inhibitors works best with cast iron engine parts, but is corrosive to aluminum and aluminum alloys
• Silicates and phosphates are abrasive, so they cause wear to water pump seals
• IAT green coolant reacts poorly with hard water, forming scale in the cooling system that can plug the radiator and heater core.
• Nitrates have a short life and don’t work well to protect aluminum or aluminum alloys.
• Pitting —As the passivating film deteriorates, the metals develop pitting and the corrosion accelerates.

Silicates and phosphates are designed to protect copper, brass, cast iron and aluminum. It is NOT recommended for use on newer cars that were filled with OAT or HOAT coolants.

Since most modern engines are built with aluminum engines, radiators, water pumps, and plastics, IAT coolant is no longer the best choice.

Organic Acid Technology (OAT) coolant type

OAT coolant is still built on an ethylene glycol bases. But they don’t use silicates, phosphates or  borates. Instead, they use carboxylic acids, azoles, aliphatic mono- and dicarboxylic acids and tolyltriazole as the.

OAT inhibitors last much longer than IAT corrosion protection. In fact, OAT can last as long as 5-10 years and up to 150,000 miles.

Advantages of OAT coolant

• Longer life
• Better able to protect aluminum than silicates and phosphates
• Non-abrasive so it doesn’t wear out water pump seals.

Disadvantages of OAT coolant

OAT coolant take longer to provide protection. In some cases they don’t reach maximum protection until 3,000 to 5,000 miles.

Hybrid Organic Acid Technology (HOAT) coolant type

HOAT coolant combines the best of both worlds. It’s main protection is provided by organic acid, supplemented by either a low concentration silicate or phosphate to provide immediate protection until the organic acids take effect.

©, 2022 Rick Muscoplat

Posted on by Rick Muscoplat



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