There are many formulations for coolant as each manufacturer has their specific formulations, however in the United States, there are three main type of engine coolant: Original Green Inorganic Acid Technology (IAT), Organic Acid Technology or OAT-Based, and Hybrid OAT G-05 and G-11 coolants. You may ask “why does this matter to me, I have a 1970 Chevelle, the old green stuff is fine.” If you have the original engine, then sure, you would be right, but if you have LS swapped that Chevelle?
IAT (Classic Green) coolant is silicate-based ethylene-glycol. It is very good at what it does, but for a very limited time. IAT coolant is good for 2-3 years, after that it doesn’t work well too resist freezing and begins to eat the rubber in the hoses and seals. It is highly recommended than any engine using IAT coolant be flushed every other year with a chemical flush and then refilled with fresh coolant. Remember, IAT coolant is toxic to all living things, so dispose of it properly.
IAT coolant does not mix well with aluminum, over time the coolant will eat away at the aluminum, including the radiator, block, and heads. This is the main reason OAT coolants were developed. If you have an aluminum radiator, you should be running OAT or HOAT coolant.
OAT coolant goes by many brand names; one such name is Dexcool. While Dex was named the culprit by shade tree mechanics in a massive recall by GM in the 1990s, the actual issue was an incompatible plastic used for gaskets. The coolant melted the plastic over time, but Dex got the blame. GM still uses the exact same OAT coolant; the gaskets were changed. This stuff has longer life, up to 10 years, but we still recommend flushing it every 3-4 years, as OAT coolants do not like air, and will sludge up over time. This is the reason that all modern vehicles have fully sealed cooling system with no vents on the expansion tanks. OAT coolant does not like copper-brass, so if you have an older vehicle with a CB radiator, IAT is going to be the best choice.
The newest type of coolant is HOAT. Because IAT and OAT coolants can NEVER be mixed (they turn to sludge immediately), a hybrid coolant was developed, using a little of both technologies. Most OEMs use HOATs now (GM is the odd duck, sticking with Dexcool). With a solid 5-year lifespan, you can safely use HOAT coolant in place of either type for 5 full years. This is the “All-Makes” coolant you see at the store.
