Automotive antifreeze/coolant is made of ethylene glycol, water, and a chemical additive package. For many years, there was only one type of antifreeze on the market, conventional green. Antifreeze technology has become significantly more complex in the last several years with the introduction of Dexcool and other extended life antifreeze formulas. Currently, there are three main types of antifreeze on the market. They all contain an ethylene glycol base, water, dye and an additive package. What makes them different is the additive package.
Conventional green antifreeze formulations usually contain a number of inorganic corrosion inhibitors that provide immediate corrosion protection because they maintain the pH of the solution (buffer it), but are consumed or transformed chemically as they perform their functions. As the coolant is heated and cooled, and exposed to air, the components of the conventional antifreeze additive package are depleted over time. This causes the pH to drop, and is why the coolant should be changed out every two years or 24,000 miles.
Dexcool-type extended life coolants use organic acid technology to inhibit corrosion, and are referred to as OAT based coolants. OAT antifreezes are touted as having longer potential service life than conventional antifreezes because of the fact that the components in the additive package are not chemically consumed as they perform their function of inhibiting corrosion. The chemicals used in the OAT type formulas protect metals from corrosion by forming a thin, molecular coating on them, and because of this, are not as fast acting as conventional inorganic formulas. However, as long as the cooling system is kept sufficiently full and coolant is not lost due to leakage nor diluted by top-off with water or conventional antifreeze, it will continue to function properly. Unfortunately, if the cooling system is not properly maintained, a “red muck” is likely to form and could cause serious cooling system problems..
Within the category of OAT antifreezes there are two broad sub-categories: 1) Straight organic acid formulations; and 2) Hybrid, or mixed OAT conventional formulations , known as HOAT (or GO-5). One of the primary problems with straight OAT formulations is that they are not compatible with conventional antifreezes. The carboxylate salts used in straight OAT antifreeze react to some extent with some of the inorganic salts and caustics used in conventional antifreeze. The result of this interaction is the generation of cloudiness and precipitates, and the loss of the extended-life properties. HOAT formulations are called hybrid because the additive package contains ingredients from both OAT and conventional formulas and is compatible with both. Hybrid OAT antifreezes provide both fast acting and extended life corrosion protection, eliminate the problem of anti- freeze compatibility, and therefore are compatible with all types and colors of antifreeze.
Hybrid OAT antifreezes partially or totally eliminate the problem of straight OAT /conventional antifreeze compatibility. Hybrid OAT (HOAT) formulations contain significant concentrations of conventional antifreeze inhibitors/ additives as well as an organic carboxylate salts. However, in this case the carboxylate salts are those that are totally compatible with the specific conventional antifreeze components used.
Unfortunately, many in the automotive industry consider all extended life antifreeze to be “Dexcool” and associate all the problems related to “Dexcool” with both OAT and HOAT formulas. The result of this misconception is often replacing the extended life coolant with conventional green. Industry experts say that this can be done safely if all of the green antifreeze is removed from the system. However, auto manufacturers recommend specific formulations and replacing the factory fill coolant with a different type that doesn’t meet the manufacturer’s specifications could cause liability issues down the road. A much safer solution is to replace OAT systems with HOAT coolant which meets OAT specifications.