Being Coolant Savvy: Avoid Mistakes, Get It Right the First Time

Posted 8/13/2009
By Jacques Gordon

It used to be simple: For a long time, antifreeze was antifreeze. It was all the same color, all smelled the same, and as far as we knew, it all worked the same way. Some of us knew that big trucks use something different (almost everything in the heavy-duty world is different), but antifreeze in cars was just something we checked every fall and changed every two years.

Not anymore. Though things began changing in the late 1980s, it was the introduction of Dex-Cool in the mid-1990s that made most of us aware that there is more than one type of antifreeze. General Motors Corp. told customers Dex-Cool would last five years or 150,000 miles, and told the service industry not to use anything else in models that were originally filled with Dex-Cool. Many of those models quickly suffered cooling system and manifold gasket failures. Though the antifreeze may not have been the real culprit (evidence exists for both sides of that argument), that's what made most of us aware that it's possible to use the wrong antifreeze.

To understand what "wrong antifreeze" means, it helps to remember what antifreeze is supposed to do when mixed with water to make coolant:

• Protect against freezing

• Increase boiling temperature

• Protect against corrosion

• Protect against cavitation damage

Antifreeze protects against freezing and boiling because it's based on an alcohol compound called glycol. Most antifreeze is made with ethylene glycol (EG), a type of alcohol made from ethane. Some antifreeze is propylene glycol (PG), a similar compound made from propane. When mixed with water, each glycol offers excellent freeze/boil-over protection, but because propylene glycol is non-toxic, it is used to make environmentally friendly coolants. Many (but not all) auto manufacturers have approved the use of PG antifreeze in their cooling systems, if it contains the correct corrosion inhibitors.

When you're servicing the cooling system, don't overlook the coolant reservoir as it may need to be flushed.

Glycol by itself is extremely corrosive. When used as engine coolant, it must be doped with corrosion inhibitors, and those inhibitors are what make one antifreeze different from another. Antifreeze manufacturers have developed three different corrosion inhibitor technologies: inorganic additive technology (IAT), organic additive technology (OAT) and hybrid organic additive technology (HOAT).

When all antifreeze was green (it can be any color the manu_facturer chooses), corrosion inhibitors were inorganic mineral salts, most commonly silicate and phosphate. These salts protect against rust by forming a surface coating on everything in the cooling system. They are effective within the first few heat cycles, but the protective coatings are not completely stable, so the inhibitor package contains enough dissolved salts to replenish the coating several times. Over time these inorganic salts are chemically consumed, and that's when IAT coolant should be changed.

What changed?

In the 1980s, most European automakers banned the use of phosphate in their cooling systems, and Japanese automakers banned silicates. When mixed with hard water, these salts can form scale and other deposits that damage water pump seals and clog heater valves that remain closed for months at a time. This was not news to anyone, but these problems became more common in the '80s as more engine parts were being made from aluminum, especially radiators and water pumps. At the same time, automakers were attempting to extend maintenance intervals, so they asked their suppliers to develop antifreeze that would do a better job of protecting aluminum and last longer than two years.

The suppliers responded with organic additive technology corrosion inhibitors, specifically, organic salts called carboxylates. Instead of coating the metal parts, these salts bond with corrosion that has already formed on the metal. This creates a boundary layer of corrosion that can't be chemically penetrated by the coolant. Similar technology is used in marine applications. It works well, and in some applications, the boundary layer can last virtually indefinitely, making extended life coolant (ELC) possible.

Unfortunately, when the inorganic salts were eliminated, cavitation damage became more common, and no other additive has proven as (cost) effective at protecting against cavitation damage (see sidebar). This is why we now have hybrid organic additive technology. As the name suggests, it's really OAT doped with tiny amounts of the same IAT salts. Today, HOAT is the most common antifreeze technology on the market and is used as the factory fill in gasoline engines by several manufacturers.

Which goes where?

Measuring coolant temperature with radiator adapter and needle-type of thermometer.

As stated earlier, regardless of glycol type, brand name or intended service life, every antifreeze on the market will be one of three types: IAT, OAT or HOAT. Any one of these can be any color the manufacturer chooses. The question is: When servicing a cooling system, how do you know which one to choose?

We asked several members of the ASA Mechanical Division Operations Committee that question. They all work in shops in different areas of the country; one shop works exclusively on European cars, another works primarily on Asian cars, and the rest see a mixture of the most common models. This was not a scientific survey, just some quick telephone conversations, but the responses present a snapshot of what people in the service industry understand about antifreeze.

When the car is in your service bay, how do you find out what coolant
belongs in the engine?

Howard Pitkow of Wagonwerx Inc. in Glenside, Pa., realizes he has an advantage here because his shop works only on VW/Audi models. This allows him to afford factory service information for everything, including fluid specifications. However, he noted that third-party information systems use the factory part number or name in their coolant specifications.

Mike Brewster of Gil's Garage in New York said, "We don't rely on color anymore." Usually he relies on his information system, but he noted they usually provide the fluid's factory part number, which doesn't really help unless he's going to buy antifreeze from a dealer parts department.

Bob Constant of Forest Hill Auto Service in Pacific Grove, Calif., looks at color first, but he's also found coolant information on under-hood labels. He also checks his information system and/or the vehicle owner's manual.

Dave Walter of Kehoe Automotive Center in Carol Stream, Ill., says finding coolant specs can be a challenge. Information systems are not always helpful, and he relies more on his good relationships with parts people at local dealerships.

Betty Jo Young of Young's Automotive Center in Houston says she'll use the specs presented in her information system when she's developing a customer estimate.

If you know the car has something other than OE coolant, how do you find out what it is?

What Is Cooling System Cavitation? Cooling system cavitation is nothing more than tiny vapor bubbles that form in liquid coolant. They form at local hot spots in the cooling system and/or in local areas of low pressure, like the inlet side of the water pump. When bubbles enter a high-pressure area, they collapse and act like tiny explosions. If they collapse in contact with metal, pitting and erosion will occur. Cavitation damage can be rapid and extensive, and its prevalence is affected by cooling system and water pump design, engine operating conditions, the condition of the cooling system and of the coolant itself.

Again, Pitkow has an advantage here because color is still a reliable marker for European OE coolants. If the coolant is the wrong color and the customer doesn't know what the coolant is, he recommends a change. He thinks VW/Audi dealer techs probably do the same.

Noting that color is "not the best way" to tell, Brewster also asks the customer, but they rarely know. He always notes on the repair order what kind of antifreeze he's installed, and it's usually brand-name HOAT.

Constant says he doesn't care what antifreeze is in the engine. When servicing the cooling system, he'll replace it with what he thinks is best for his customer, usually an aftermarket long-life coolant.

Walter will also replace the coolant, but he likes to use whatever the OE recommends. If it's a late-model GM car with green coolant, he'll recommend a flush and refill with Dex-Cool.

Young, who is not a tech, says that for some makes/models, color is still a good indicator.

How do you decide what type of antifreeze to use?

Pitkow's supplier sells him the same stuff that dealers use. It has a VW/Audi part number and logo on the bottle, making it a genuine part. VW also specifies which OE coolants can be mixed with standard "green" aftermarket coolant.

Brewster says his first instinct is to check the label (for silicates, etc.). Experience with certain brands helps him make the decisions faster.

Constant buys the standard "green" antifreeze in bulk and everything else in jugs. He'll keep some jugs of OE antifreeze in stock and says he has five or six different types in the shop at all times because "we don't want a dealer telling our customer we've put in the wrong coolant."

Walter buys only OE antifreeze, or whatever the manufacturer recommends. "I'm not going to re-engineer this car. What the manufac_turer recommends is what works." He keeps the most common OE antifreeze in stock and says some are available aftermarket.

Young buys antifreeze in bulk from reputable parts dealers, but on each job she makes sure the tech is using the right kind. "We've got to be really careful. (In summer) you don't wanna be broke down on the highway in Houston."

It seems people are still relying at least partly on color to identify coolants, but that's understandable since even the OEs use color to describe their own antifreeze. Still, it's apparent that knowing which antifreeze to use requires some investigative skill. In this business, that's just one of many skills that defines you as a professional. So use that skill to choose your colors wisely.

Photos courtesy of Brian Manley.

Jacques Gordon is a freelance technical writer living in Chester County, Pa. Formerly the technical editor of Motor Age magazine, he has also worked as a fuel systems lab technician, a dyno lab technician and an auto mechanic. He can be reached at jgordon3663@gmail.com.