Cooling System Antifreeze Requirements

Cooling System Antifreeze Requirements

When a customer brings you a vehicle that needs a coolant change, what kind of coolant should you use? The type of coolant specified by the vehicle manufacturer? A universal or “all makes, all models” type of coolant? Or should you run the old coolant through a recycling machine and put it back in the system? All are valid options for servicing today’s vehicles, but the options are not without controversy.

Before Dex-Cool was introduced back in 1995, almost every domestically produced vehicle used a traditional “green” formula inorganic acid technology (IAT) coolant. The Japanese and European automakers had their own versions of this formula. But as far as the aftermarket was concerned, the same stuff worked just fine no matter what you poured it into. So in that respect, green coolant was essentially a universal all makes, all models type of coolant for its day.

Then things got complicated. GM specified its orange-colored Dex-Cool coolant, which used a totally different kind of additive package based on organic acid technology (OAT). Ford and Chrysler opted for a hybrid version (HOAT) formula that added silicates to increase aluminum protection. The Japanese and Europeans both developed their own OAT formulas, with the Japanese adding phosphates while the Europeans took out phosphates. Everybody decided to dye their coolants a different color, which only added to the confusion because there was no standardization — which meant the colors were essentially meaningless as far as what was actually in the formula.

The aftermarket has always had a knack for simplifying things the OEMs have complicated, and coolants are no exception. Coolant suppliers who have tried to meet the conflicting OEM coolant requirements now market three basics types of coolant: the traditional green formula, plus an orange formula that meets GM’s Dex-Cool 6277 specification, and a yellow hybrid (HOAT) formula for Ford, Chrysler and all the rest.

Universal Coolants
Coolant suppliers who say this is so much nonsense have developed their own proprietary OAT-based products, which they say can be safely used in all makes and all models. The Better Business Bureau challenged one coolant supplier on this claim, insisting there can be no such thing because the vehicle manufacturers all have different and sometimes conflicting coolant specifications.

Even so, those who make universal coolants argue their additive packages have been thoroughly tested and meet all applicable ASTM (American Society of Testing Materials) and SAE (Society of Automotive Engineers) specifications. They say their coolants can safely protect both cast-iron and aluminum engines and radiators, regardless of what kind of vehicle they are in. What’s more, their universal coolants will protect just as long as the OEM coolants, which is five years or 150,000 miles in most late-model vehicles.

If you’ve visited the automotive department in your local Wal-Mart or almost any retail auto parts store recently, it’s obvious which way the retail market has gone on this issue. The only coolant you’ll usually find on the shelf is a universal product. Some stores still carry the green formula coolant for older cars, or for customers who are looking for the least expensive coolant they can find. But most have discontinued the GM-, Ford- and Chrysler-specific coolants and replaced them with a single product. That approach, they say, reduces their inventory requirements (one SKU versus several) and it eliminates customer confusion about which product to buy.

Green coolant is also getting harder to find because the vehicle population that uses it is shrinking every year. Taking it off the shelf also reduces the risk of cross-contaminating coolants. Topping off a late-model cooling system that contains an OAT or HOAT type of coolant with ordinary green coolant can reduce the overall life of the coolant in the system to that of the green coolant (which is typically two to three years or 30,000 miles).

The additives used in the older green formula coolants have a totally different chemistry than that used in today’s OAT and HOAT formula coolants. It’s very difficult, if not impossible, to detect coolant cross-contamination by looking at the color of the coolant. There may be some color change when coolant that contains green dye is mixed with coolant that contains yellow, orange or another color dye. But the color alone won’t tell you anything about the chemistry of the mixture, or how much of one has been mixed with another. That’s why coolant suppliers take a conservative approach and say mixing green IAT formula coolant with an OAT or HOAT formula coolant will shorten the overall life of the mixture.

You can look at things like reserve alkalinity to determine how much corrosion protection is left in used coolant, and test strips designed for IAT coolants and OAT/HOAT coolants are available for this purpose. But if you have a mixture of the two, are the results reliable? And which test strip do you use? IAT coolants actually provide a higher level of alkalinity than OAT and HOAT coolants. But the level drops more quickly as the additives are used up.

Still Three Basic Types of Coolants
In addition to universal coolants, there are still three basic types:


Traditional North American green antifreeze. This was the factory fill for Ford, GM and Chrysler vehicles up until the mid-1990s. The inorganic acid technology (IAT) coolant contains fast-acting silicate and phosphate corrosion inhibitors that protect cast-iron engines, bimetal (cast-iron/aluminum) engines, and copper/brass and aluminum radiators. But the short-lived nature of the corrosion inhibitors means this type of coolant should be changed every two to three years or 30,000 miles (though some products now claim a service interval of up to 50,000 miles with improved chemistry).


This type of antifreeze is primarily used for older vehicles (pre-1996), but can also be used in virtually any vehicle application (domestic, Asian or European) regardless of year — provided all of the old coolant is completely flushed and replaced with new.

OAT-based extended-life coolants. Organic acid technology formulas include such ingredients as sebacate, 2-ethylhexanoic acid (2-EHA) and other organic acids, but no silicates or phosphates (except in the case of Toyota’s pink extended-life coolant, which adds a dose of phosphate to its extended-life OAT-based antifreeze). OAT-based coolants are usually (but not always) dyed a different color to distinguish them from regular North American green antifreeze. GM’s OAT-based Dex-Cool is orange. Volkswagen/Audi uses a similar product that is dyed pink. But Honda has an extended-life OAT coolant that is dyed dark green and does not contain 2-EHA.



The corrosion inhibitors in OAT coolants are slower acting but much longer-lived than those in traditional North American green coolants. Consequently, OAT coolants typically have a recommended service life of five years or 150,000 miles.

OAT corrosion inhibitors provide excellent long-term protection for aluminum and cast iron, but may not be the best choice for older cooling systems that have copper/brass radiators and heater cores. Some sources do NOT recommend Dex-Cool or other OAT coolants for older vehicles with all-iron engines and copper/brass radiators. Others say OAT coolants can be safely used in older vehicles as long as you follow the original OEM service interval for changing the coolant (typically two to three years or 30,000 miles).

Hybrid OAT coolants, also known as “G-05.” This formulation also uses organic acids, but not 2-EHA (different organic acids are used). Hybrid OAT coolants add some silicate to provide quick-acting protection for aluminum surfaces. Silicate also helps repair surface erosion caused by cavitation in the water pump. Hybrid OAT coolants are currently used by many European vehicle manufacturers as well as 2001 and newer Chrysler vehicles, 2002 and newer Ford trucks and SUVs, 2003 and newer Ford passenger cars, and 1985 and newer Mercedes, BMW, Volvo and Mini Cooper. The service interval is the same as OAT coolants: five years or 150,000 miles.



Just remember that no coolant is a lifetime coolant. The coolant may last a long time, but, eventually, the corrosion inhibitors wear out. Many motorists don’t know this and falsely assume they never need a coolant change. Consequently, when they neglect the coolant, they can experience radiator, heater core and freeze plug failures from internal corrosion.

Premix vs. Full Strength
Another trend you’ll see at the retail level is the increased availability of premixed 50/50 coolant. One of the advantages of selling premixed coolant is that it is more profitable, especially if a vehicle owner is changing their own coolant and buys several gallons. Although the price per gallon may be a couple of bucks less for premix compared to full-strength antifreeze (which seems like a savings), consumers actually end up paying more per gallon for the antifreeze that is in the jugs because the jugs are half full of water.

From the consumer’s perspective, premix is a much more convenient product to use because it eliminates the need for mixing. From a technical standpoint, premix is also better for the average motorist because it contains pure, distilled water. There’s no danger of introducing dirty water, softened water (which contains corrosive salts) or hard tap water (which can be loaded with minerals such as calcium, magnesium and iron) into the cooling system. Distilled or deionized water is a must when mixing coolant to maximize the life of the additive package in the coolant.

Premix also helps to maintain the concentration of the coolant at the proper ratio. A 50/50 mix is usually recommended for most applications because it provides the best combination of boiling and freezing protection. Up to a 70% mixture of antifreeze can be used in extremely cold climates to lower the freezing point of the coolant, but the trade-off is reduced cooling efficiency because ethylene glycol (the main ingredient in antifreeze) carries heat less efficiently than straight water. If the concentration of antifreeze to water is too high in hot weather, it may increase the risk of the engine overheating.

Many professional technicians are also opting for premix because it saves time, mixing and mess. It’s great for topping off customer’s cooling systems. But if you are doing a complete flush and fill, you’re probably better off using concentrate to more accurately control the strength of the coolant. Flushing can leave a lot of water in the block, so if you just add 50/50 premix, you may end up with too much water and not enough antifreeze in the system.

More of the Same?
We contacted the major coolant suppliers to see if any of the vehicle manufacturers have changed their coolant requirements. None have, so the basic recommendations still remain unchanged. GM specifies Dex-Cool, Ford and Chrysler specify a silicated hybrid coolant, and the Japanese and Europeans have their own silicated HOAT formulas.

As for the suppliers of universal coolants, their claims have not changed either. They still say their products will work in all makes and all models regardless of what type of coolant the vehicle manufacturer specifies.

Down the road, there may be an emerging market for antifreeze that uses a different base stock other than ethylene glycol. Glycerine-based coolants are now being used in some heavy-duty diesel truck applications. Glycerine is still too expensive compared to ethylene glycol for general automotive use, but it can be made from the byproducts of biodiesel production (which may be a greener alternative to using crude oil or natural gas as a base stock to manufacture ethylene glycol). Another advantage for glycerine is that it is non-toxic, which eliminates any worries about accidental poisoning from ingesting ethylene glycol. Glycerine has similar thermal characteristics to ethylene glycol, but boils more than 150° higher, making it well-suited for hard working, high temperature applications. Ethylene glycol’s boiling point is about 388° F, and glycerine is closer to 550° F.

Magnesium engines may also require a new coolant additive package. Today’s OAT and HOAT coolants can’t adequately protect these engines. So if lightweight magnesium engines coming to widespread use, look for yet another coolant formula. In 2004, BMW introduced an all-new super light 3.0L six-cylinder engine with a bimetal aluminum/magnesium block. The walls of the block are magnesium, but the cylinders and cooling jackets are aluminum, which allow the use of an ordinary coolant.

What about Coolant Recycling?
If you’re concerned about used coolant disposal issues, a coolant recycling machine is an alternative to draining and refilling your customer’s vehicles with fresh coolant. Recycling machines clean and recondition the old coolant so it can be reused. This can reduce the waste stream from your shop, and saves you the cost of buying new coolant. However, you have the initial cost of buying the recycling machine, and the ongoing expense of chemicals and other supplies needed to operate and maintain the equipment.

Ethylene glycol never wears out. But the chemical additives in the antifreeze that prevent corrosion are used up over time. The coolant can also become contaminated with rust and scale that forms inside the engine and radiator. Consequently, the coolant either has to be replaced, or cleaned and rejuvenated with a fresh dose of additives.

Coolant recycling can be done in a variety of ways, but most recycling machines designed for shop use employ a filtration process and chemical reaction to remove contaminants. The coolant is pumped though a filter (sometimes more than once), and additional chemicals (flocculants) may be added to precipitate out other impurities such as emulsified oils and heavy metals. After filtering, an additive package and dye are added to restore the appearance and chemical properties of the coolant.

The effectiveness of the cleaning process can vary from one type of recycling equipment to another. A distillation process is the most effective, but also takes much more time and requires more complex and costly equipment. Distillation is typically used for batch processing by coolant recyclers.

Changing the Coolant
Regardless of what type of coolant you opt to use in a customers’ vehicle, you need to replace as much of the old coolant as possible when changing the coolant. A simple drain and fill is not a complete coolant change because up to half of the old coolant may remain trapped inside the engine block. A simple drain and fill can also introduce air into the system, which can be difficult to remove later when the system is refilled. Trapped air may cause the engine to overheat.

To avoid these kinds of problems, a complete coolant exchange should be done using a coolant flush/exchange machine. The equipment connects to the radiator cap, and upper radiator hose or heater hoses with adapter fittings. Most are capable of replacing almost all of the old coolant (90-95%) with fresh coolant in 10-25 minutes. Automatic controls eliminate the need to babysit the equipment, and many machines include a pressure test to ensure the integrity of the cooling system. The machine may be electric powered (12-volt DC or 110-volt AC) or pneumatic (125 psi shop air).

Because a coolant exchange machine is replacing liquid with liquid, air is kept out of the system so you don’t have to worry about air pockets that might cause the engine to overheat.

Many coolant exchangers also reverse flush the system to dislodge sediment, rust and scale as the coolant is being replaced. A pulsing action may be used to increase the effectiveness of the cleaning system. This also eliminates the need to flush the system with water, which takes extra time and creates additional waste and disposal issues.

One other check that is often overlooked when servicing coolant is to check for electrolysis. Stray electrical currents that use the coolant as a conductor can rapidly corrode heater cores, radiators and other metal parts in the cooling system. Electrolysis can occur when the corrosion inhibitors in the coolant break down and/or when electrical loads can’t find a normal path to ground except through the coolant. A common cause is loose, corroded or undersized ground connections between the battery, charging system, engine or body.

Electrolysis can be checked with a digital voltmeter by dipping one probe into the coolant and touching the other to battery negative or ground. The check should be made with the engine idling and a heavy load on the charging system (lights and other accessories on). Anything over 400 millivolts is too much.

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