Chrysler switches to OAT antifreeze for longer service interval

  • 22-Aug-2012 08:09 EDT

Label on this early production 2013 Dodge Dart coolant reservoir says it’s an “OAT Coolant,” but it’s a special type. It  should not be mixed with the previously used G-05 silicated coolant or versions of the “DexCool” recommended for GM and Ford products.

Chrysler, the last of the Detroit 3 car makers to use a silicated antifreeze, has switched to an organic acid technology (OAT) formula for the 2013 model year. The change to an “OAT” might have been anticipated with the acquisition by Fiat, but the Chrysler-selected OAT formula, although it shares a major inhibitor, is not the same as used by Fiat.

Ford made the changeover starting over two years ago, with a major objective to standardize on a single world coolant. It set a moderate six-year, 100,000-mi change interval (160,000 km) for a new car, followed by every three years or 50,000 mi thereafter (80,000 km). General Motors, which was the first U.S. automaker to use an OAT, recommends a service interval of five years, 150,000 mi (241,402 km).

At Chrysler, the objective was to be able to pass an engineering test for a 10-year, 150,000-mi coolant service interval—which becomes the most aggressive schedule of the Detroit-3 makers. Although extended coolant service intervals have been promoted by environmentalists to reduce coolant waste and possible inappropriate dumping, the 10-year/150,000-mi interval reportedly was just a competitive maintenance decision by Chrysler.

The new antifreeze replaces G-05, a low-silicate BASF formula (called a “hybrid OAT”) made in the U.S. by Zerex (Ashland Inc.) and that also had been the Ford choice until 2010. Silicate inhibitors have been used for many decades, and antifreeze chemists still may admit there is no equivalent substitute. It forms a durable coating on the walls of the cooling system, and because it works so quickly, it re-establishes protection within the water pump if the surface becomes pockmarked by imploding coolant bubbles from cavitation. The pockmarked surfaces, if left unprotected, would corrode.

Organic acids form an oxide coating that provides comparable and often much longer-lasting protection, but it takes about 5000 miles (8000 km) to form, during which time corrosion may occur. When Ford made the change, it said it had modified the cooling systems of its cars where necessary to minimize cavitation, and it began a phase-out of the 4.6-L and 5.4-L V8s, which were considered unsuitable for use with an OAT.

Chrysler told AEI it had been running dynamometer tests of cooling systems for the past year to ensure water pump cavitation erosion corrosion would not be a measurable issue. The use of highly purified water in every OEM coolant fill (50-50 mix with antifreeze) also helps to protect the system until corrosion protection is established. But following the OEM fill, the quality of the water and the compatibility of the antifreeze chosen for top-ups and an eventual flush-and-fill cannot be ensured. A mere 17% mix with an incompatible antifreeze is sufficient to accelerate system corrosion.

Extra sealing protection

Neither Chrysler nor Fiat has released the complete composition formula for their antifreezes. They reportedly are cocktails of three organic acids, featuring sebacate, but no 2-ethylhexanoate (2-EHA). The latter is a cost-effective but controversial additive that softens plastics, particularly silicone, leading to leaks from affected sealing materials, which means that silicone cannot be used in gaskets, O-rings, and hoses if the antifreeze contains 2-EHA.

Although 2-EHA is not in the Chrysler or Fiat formulas, silicone sealing materials aren’t used either, said Chrysler’s Tom Lawrence, Senior Manager, Engine Design and Development. He told AEI the decision was made to provide an extra layer of sealing protection for service replacement parts. In addition, the possibility of aftermarket flushing the system and replacing the OEM antifreeze with a coolant containing 2-EHA had to be considered, he added.

The OAT formulas approved by GM, called DexCool, contain 2-EHA and in most cases, sebacate, but there is no specific composition formula, only a performance test. Major aftermarket brands, such as Prestone, are DexCool-type formulas with 2-EHA, but in most cases without the DexCool label, as it’s a GM brand name that commands a royalty payment.

The performance test for DexCool formulas, which have de facto Ford approval, are designed to exclude both silicates and phosphates, an alternative to silicates used in all Asian OEM formulas. Phosphates and silicates long were combined in a formula called “conventional American” antifreeze. That type typically had a recommended service life of only two years or 30,000 miles (48,000 km).

The dye color of antifreeze has nothing to do with antifreeze formula or performance. Chrysler’s G-05 contains orange dye to distinguish it from a yellow dye antifreeze previously used. Other users of G-05 have yellow or even blue dye. However, GM DexCool, a purely organic acid type, also has orange dye, and this has been a source of service industry confusion. Fiat’s OAT, although a different formula, also has orange dye and it has been used in early production of the Dodge Dart. The new Chrysler OAT, however, will have a purple dye.

Petronas Lubricants is the Fiat supplier. CCI Manufacturing will provide the Chrysler OAT.

Daimler sticks with silicate-based formula

Silicates eventually are depleted in normal operation, and there are severe laboratory tests that cause it to drop out of solution. Those Asian companies that require these tests, primarily the Japanese makers, will not use silicates. Their phosphate alternative has a similar coating action but is not as durable and depletes over time. It also will not pass European car makers' tests with extremely hard water, with which they form scale deposits.

However, phosphate does enhance protection. Without it, Japanese makers have said, antifreezes will not pass their engineering tests. Asian service intervals typically are up to five years or 100,000 miles.

One major automaker still using a silicate formula with a long service interval is Daimler. Its engineering approach permits a service interval of 15 years/150,000 miles. Daimler’s “secret” is a silica gel packet, similar to what is used with electronics packaging, in the coolant reservoir. Daimler has found it gradually releases enough silicate to “refresh” the antifreeze. However, it recently replaced the G-05 with G-48, another low-silicate formula with sebacate, only a dash of 2-EHA and reduced borate. The two are compatible, and Mercedes dealers are treating them as interchangeable.

BMW and VW/Audi also use formulas with low silicate content in combination with similar OAT mixtures.

Unlike G-48, G-05 also contains nitrite, an additive that helps prevent diesel wet cylinder liner pitting corrosion. It reportedly was part of the protection package that Daimler required when it first approved the formula over 30 years ago. Nitrite cannot be used in an OAT formula, but diesel engine OEMs have found that the diesels in their cars and light/medium duty trucks enjoy satisfactory life with the OATs. The Cummins diesel, for example, passed Chrysler testing with its OAT, Lawrence said.

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