| Under The Cap,
Larry Carley, Tire Review, November 2000
Today's Coolant Options Require Close Attention, Different Techniques When you open a radiator cap these days, you're never quite sure what you're going to find.
Antifreeze chemistry has undergone some significant changes in recent years, and the familiar green antifreeze long used in most vehicles is being replaced with a spectrum of not-so-familiar antifreezes that range in color from red to orange to pink to blue.
So it's important to know what type of antifreeze is in the system so you can add a compatible coolant, or replace it with one that provides equivalent or better protection.
Ethylene Glycol Ethylene glycol (EG) has been the main ingredient in almost all automotive antifreezes for many years, and will continue to be for the foreseeable future. Straight ethylene glycol freezes at about 8° F, boils at 330° F, and carries heat about 15% less efficiently than water. But when mixed in equal parts with water, it creates a coolant well-suited to year-round driving for most applications. The recommended 50/50 mixture of EG and water provides freezing protection down to -34° F and boilover protection to 265° F in a radiator with a 15 psi cap. If the proportion of antifreeze to water is increased to 70% EG and 30% water, the freezing point drops to -84° F and the boiling temperature goes up to 276° F. Mixtures greater than 70/30 are not recommended because the coolant's ability to carry heat declines as the proportion of antifreeze increases.
Straight EG antifreeze should never be used in an engine because it may allow the engine to overheat. Likewise, straight water should never be used because it provides no freezing, boiling or corrosion protection.
Propylene Glycol Another base ingredient that is used in place of EG in some aftermarket antifreezes (like Prestone's LowTox and Safe Brands' Sierra antifreeze) today is propylene glycol (PG). The coolant's thermal characteristics are similar to those for EG: a 50/50 mixture of PG and water provides freezing protection down to -26° F and boilover protection to 256° F. If the coolant mixture is increased to 60/40, coolant freezing protection goes down to -54° F. The main advantage of PG compared to EG, however, is that it is considered nontoxic to animals. That doesn't mean it is safe to drink, but it greatly reduces the risk of poisoning a pet. Pure PG boils at 370° F and provides freezing protection down to -70° F, so it is sometimes used straight without any water at all as a coolant in racing applications. Running PG straight provides better cooling because there is no water to vaporize in hot areas of the cylinder. This also allows the use of very low pressure or even no pressure cooling systems.
While PG and EG are both compatible and can be intermixed without affecting cooling performance, intermixing the two different antifreezes is not recommended because doing so defeats the reduced toxicity advantages of PG. Also, if a vehicle's cooling system is filled with an extended life EG coolant, adding PG - not currently formulated for extended service - will reduce the service life of the coolant mixture to that of a conventional green coolant.
Intermixing PG and EG antifreeze also makes it impossible to get an accurate indication of the coolant's strength if you're using a hydrometer to check coolant concentration.
The specific gravity of EG and PG are different, so a mixture of the two will usually indicate a lower freezing point than the coolant actually provides. The best way to determine the concentration of PG in uncontaminated coolant (no EG present) is to use a refractometer. The reason is because the specific gravity of PG increases up to about a 70% concentration, then falls off considerably. Consequently, a 100% PG solution will read the same as a 45% solution on a hydrometer.
General Motors and others approve PG as an acceptable replacement coolant, but if making a change it's important to remove all of the old EG coolant before adding PG to the system.
Because coolant is in constant contact with the metal parts of the engine and radiator, some type of corrosion inhibitors must be used in the antifreeze to protect all metal surfaces from electrolysis.
That includes cast iron, steel, aluminum, brass, copper and lead solder.
Most conventional antifreezes formulated for the North American market, whether green or yellow in color, contain inorganic salts of borate, phosphate and silicate to prevent rust and corrosion.
The additives create an alkaline coolant mixture that typically tests at about 10.5 on a pH scale. The silicates form a protective coating on metal surfaces, and are especially good at protecting aluminum. To ensure that coolant remains alkaline for a reasonable length of time, there must be enough corrosion inhibitor to neutralize the acids formed from glycol degradation that occurs over time.
This neutralizing capability is called "reserve alkalinity," and it varies depending on the type and quantity of additives used in a particular brand of antifreeze. Heat, dissolved oxygen, minerals in the water, and corrosion inhibitor reactions at the metal surface gradually use up the corrosion inhibitors. And once depleted, the coolant becomes acidic and corrosion accelerates.
The secret to preventing internal corrosion, therefore, is to change the coolant before all the reserve alkalinity has been used up.
Periodic coolant changes are especially important with today's bimetal engines and aluminum radiators and heater cores because the different metals create a miniature battery cell that promotes electrolytic corrosion.
Aluminum becomes the sacrificial anode, iron the cathode, with the coolant serving as the charge-carrying electrolyte. The higher the percentage of dissolved minerals and salts in the coolant, the better it conducts electricity and the faster the aluminum is eaten away.
As long as the corrosion inhibitors are working, the process is held in check. But once they're used up, corrosion starts to eat away. The most vulnerable components are usually the thinnest, which include the radiator and heater core.
The Effect of Air & Water
Other problems can also accelerate the breakdown of the coolant. An exhaust leak into the cooling system through a cracked head or leaky gasket will quickly destroy reserve alkalinity in the coolant because oxygen reacts with the additives in the antifreeze. If an engine has a leaky head gasket, don't reuse the old antifreeze when the gasket is replaced. The amount of additive needed to protect the cooling system isn't much - only about 2% to 3% of the total liquid in the jug. This is usually enough to protect for at least two years or 30,000 miles in most vehicle applications - or even longer if the antifreeze is mixed with relatively pure water (distilled or deionized).
Some say ordinary antifreeze can go as long as five years or 100,000 miles before the corrosion inhibitors are fully depleted - provided pure water is used to fill the system, the cooling system was relatively clean when filled (no accumulated rust or scale), and the coolant level is kept full with no air entrapment.
Hard water that contains high amounts of calcium and magnesium can react with phosphates in the additive package to form sediment and scale. That's why European vehicle manufacturers use antifreezes that contain no phosphates (hard water is common in Europe). European antifreeze may be dyed blue, yellow (Mercedes) or pink (VW and Audi). Tap water in North America also contains calcium, but isn't as hard as European tap water so phosphates are considered okay to use here. Under no circumstances should softened water be used in a cooling system because softened water substitutes sodium (salt) for calcium.
Sodium is very corrosive to all metal surfaces and undermines the corrosion-inhibiting abilities of the additives.
The Japanese and other Asian vehicle manufacturers, by comparison, prefer an additive package that contains phosphates and other inhibitors but no or low silicates. Japanese coolants may be dyed red, but some newer blends are dyed green.
According to the aftermarket antifreeze suppliers we interviewed, using a typical green antifreeze formulated for North American domestic vehicles in European or Japanese vehicles should cause no problems. The basic metallurgy is the same so the degree of protection provided should be the same: two years or 30,000 miles.
The latest corrosion inhibiting additives are based on a different chemistry called Organic Acid Technology (OAT). Antifreezes with OAT corrosion inhibitors contain organic acid salts of mono- and dicarboxylic acids such as sebasic and octanoic acids, plus tolytriazole.
The coolant is less alkaline and protects with a pH reading of only about 8.3.
Brands with the OAT additive package include Texaco/Havoline's Dex-Cool and Prestone's Extended Life 5/150 antifreeze.
OAT coolants contain orange dye to distinguish them from other coolants with conventional additive packages. The main advantage of OAT technology is extended service life: up to five years or 150,000 miles. But to achieve this length of service, the OAT coolant must not be intermixed with any other type of antifreeze.
If the system is topped off with ordinary green antifreeze, the corrosion protection will be reduced to that of a conventional coolant, say the coolant makers.
GM was the first domestic vehicle manufacturer to make the switch to OAT coolants, starting in 1995. Since 1996, all new GM cars and light trucks have been factory-filled with orange Dex-Cool coolant. GM says Dex-Cool can be used in older vehicles provided the cooling system is first flushed to remove all traces of conventional coolant. But people have said OAT-based coolants do not provide adequate protection for vehicles with lead-soldered copper/brass radiators - a charge the makers of OAT antifreeze say is not true. Texaco/Havoline and Prestone both say their products meet or exceed the ASTM D-2570 standards for corrosion protection.
There has been some controversy regarding the use of OAT coolants because of sludging problems GM experienced in some 4.3L S10 truck engines.
GM service bulletin #99-06-02-012 says the sludging problem is caused by air pockets in the cooling system from failing to maintain the coolant level or not getting all the air out the system when refilling the cooling system. GM's fix for the condition is not to switch back to a conventional coolant (which some people advocate), but to flush the system repeatedly until all the brown sludge has been removed. The system can then be refilled a 50/50 mix of Dex-Cool and clean water.
Despite the problems with the 4.3L truck application, the use of OAT antifreeze is expected to grow.
DaimlerChrysler introduced its own extended service OAT hybrid coolant for passenger cars in 1998. Unlike Dex-Cool, the DaimlerChrysler coolant contains silicates for extra aluminum protection. DaimlerChrysler, however, does not recommend using their OAT hybrid in older vehicles.
Ford in North America is still using conventional additives in its antifreeze, with the exception of the 1999 and up Mercury Cougar which now uses an OAT coolant. But Ford of Europe has switched over to OAT antifreeze for many of its vehicles.
Truck manufacturers including Navistar, Mack and Caterpillar have also approved OAT.
Coolant Checks Important
One problem we have in is that we have no way of knowing what kind of antifreeze is in a customer's cooling system when it comes into the shop. It may be the factory-fill coolant, it may be an aftermarket coolant, it might be a propylene glycol coolant, or it might be a mixture of several different types of coolants. If you don't keep these possibilities in mind, a simple coolant check with a hydrometer may give you a false indication of the strength of the coolant.
A refractometer is a better tool to use because it doesn't measure specific gravity but how the liquid bends light. Chemical test strips are available to check both the concentration and condition of the coolant, too. But test strips designed for conventional green coolants won't give an accurate indication of the coolant's condition if used with an OAT type of coolant.
Coolant Service Tips
Though most coolant service consists of flush and fill, ethylene glycol coolants can also be recycled using the proper equipment (see sidebar below). Recycling has obvious environmental benefits, and can be a source of additional profits for your tire store.
EG coolants with OAT additives can also be recycled, but the aftermarket additives currently available only return the coolant to a standard two-year/30,000-mile silicate coolant. When refilling a late model GM vehicle that was factory-filled with Dex-Cool, you have to decide what type of coolant to use. According to GM, Dex-Cool is the only acceptable coolant. But once the vehicle is out of warranty, there's no reason why you can't use another brand of OAT coolant or a conventional EG or PG coolant, say the makers of these products.
The same goes for using an OAT coolant in an older vehicle that contains a conventional green coolant. If the system is thoroughly flushed, you can give your customer the extended service benefits that an OAT coolant provides.
OAT coolants can also be used to refill European and Asian vehicles, provided the system is first flushed to remove all traces of the old coolant.
The National Automobile Radiator Service Association (NARSA), however, is more cautious about the use of OAT coolants. NARSA says OAT coolant should not be used in any Ford product (except the 1999 Cougar) or Chrysler vehicle because there is a risk of water pump cavitation erosion.
GM reportedly redesigned its water pumps to eliminate cavitation erosion.
Regardless of what type of coolant is used to refill a cooling system, the system should be cleaned if sediment, rust or scale are present. Also, the system should be pressure tested to make sure there are no leaks. And don't forget to pressure test the radiator cap, and inspect the belts and hoses, too.
Refilling some of today's vehicles can be tricky if the heater core or other hoses are higher than the radiator cap. If the system has bleeder valves, use them. If it doesn't, it may be necessary to jack up the front of the vehicle so the radiator cap is the highest point in the system.