The Petroleum Quality Institute of America (PQIA) fielded a number of calls and emails following publication of test results for three brands of antifreeze (also known as coolants) last week. In addition to expressing dismay about the product (click for details) on the retail shelf with only 8% ethylene glycol and a freeze point of positive 27°F, several who reached out to PQIA also had questions about the differences in the colors of products in the market. Understandably, this is a common question since coolants are available in a relatively wide range of colors and the colors are often associated with significant differences in price. As an example, the price of green coolant can be nearly half the price of pink.
So, what’s the difference? As one caller asked, “Why would anyone want to pay twice the price for one color coolant instead of another since they all offer nearly the same freeze protection?”
This question comes as no surprise since the word “antifreeze” can easily be interpreted as meaning the purpose of the fluid is to prevent a radiator/engine from freezing. But as those familiar with these fluids know, its primary purpose is to prevent an engine from overheating (remove excess heat). The fluid does so by absorbing the heat of combustion and transferring it to the radiator where it can be dissipated to the surrounding air.
Due to its outstanding ability to both absorb and transfer heat, water is the fluid of choice for cooling engines. But, although it excels in heat transfer, it comes with its own set of issues; first it freezes at 32°F. If it freezes, it can cause serious damage to the cooling system and engine. Considering that every U.S. state experience temperatures at or below freezing, although it’s an excellent coolant, water is mixed with another fluid to depress its freeze point (typically ethylene or propylene glycol). Along with its ability to lower the freeze point of the coolant, at the other end of the temperature spectrum, ethylene and propylene glycol is also valued for its ability to raise its boiling point.
But there is more. Whereas the water and glycol mixture provide engine cooling, and freeze and boil over protection, the coolant and the environment in which it operates bring with it additional issues that must be addressed. These issues primarily include corrosion, scale, deposits, and aeration/foaming. The different additive chemistries required to address these and other issues, as well as vehicle manufacturer specifications, brings us to the variations in coolant colors.
In short, color typically denote differences in the chemical composition of coolants and its suitability for use in various vehicle make and model years. As shown in the PQIA Quick Reference Guide, the type of coolant recommended differs by vehicle manufacturer. Importantly, however, although the color is typically associated with the coolant type, there are no industry standards defining the color for each type. As such, whereas color is a good indicator, the specifications on the label is the arbitrator.
Coolant Additives and Colors
Coolant comes in contact with a variety of metals in an engine and its cooling system. These metals include iron, aluminum, copper, lead and other materials that can corrode when exposed to water and other chemicals in the cooling system. Because of this, coolant contains inhibitors to help protect engine and cooling system components from corrosion. In addition, coolants contain chemicals to reduce its tendency to foam, prevent oxidation, balance pH, and because ethylene glycol is toxic, some U.S. states require bitterant is added to the coolant as an aversive agent to discourage ingestion by giving it a bitter taste.
Coolants also contain dyes that give them their distinct colors. The dyes provide a visual cue to help users identify the product as coolant and differentiate between various types (chemistries) of fluids in the market. Although one could write a book about the chemical formulations defining coolant types, and some have, there are basics to keep in mind when considering a purchase. The first, and most important, is that car manufacturers specify the type of coolant for the make and model years they produce, and there are significant differences across car manufacturers. Second, use of a coolant other than the type recommended by the manufacturer can compromise the performance and life of the engine and cooling system. In addition, it can result in voiding a new car warranty. So regardless of the color of a coolant, it is very important to read the label on the product to make sure it meets the vehicle manufacturer recommendations. But with that said, the color of coolant does have value.
The makes and models of vehicles require certain types of coolants and the color helps to identify fluid types. Florescent green for example, is a color commonly used to identify a product with Inorganic Acid Technology (IAT) generally referred to “Conventional Coolant.” This type is specified for use in most Ford cars built prior to 2003. Following that year, Ford specified the use of Hybrid Organic Acid Technology (HOAT). This type of fluid is commonly yellow and was also specified in most Asian manufactured vehicles prior to 1996. Unlike many of the other car manufacturers, however, most Asian vehicles switched from HOAT to Phosphate Organic Acid Technology (POAT) in 1996.
So, there is more to coolants than just freeze protection and there are good reasons for the colors and price differences seen in the marketplace. And in addition to those associated with color, there are other important differences in coolants that consumers should look for. Whereas some, for example, are ready-to-use prediluted (50/50 mixtures of water and ethylene glycol), others are concentrates that must be mixed with water by the consumer prior to use. Differences can also be seen in the service life of coolant. Some for example are formulated for extended life service (i.e. 150,000 miles).
The PQIA Quick Reference Guide below is provided to help consumers understand the differences in coolant types and their applications. Always consult your owner’s manual to assure you know what type of coolant is recommended for your vehicle and read the labels before purchasing a coolant to help assure you make the right choice.