LO 11-5 Describe and explain the classification, composition, and applications of various antifreeze formulations

1. Antifreeze Formulations

Antifreeze Formulations

The mixing of ethylene glycol or propylene glycol antifreeze and water alone is not an effective method to prevent the corrosion or erosion of cooling system components. In fact, the addition of antifreeze to water causes additional chemical reactions that require control. For example, ethylene glycol becomes acidic and corrosive when exposed to air; propylene glycol is also highly corrosive to a few metals. Foam suppressants, also called wetting agents , need to be added to maintain coolant contact with engine parts because steam and other vapor bubbles do not cool well. The development of antifreeze formulation is an evolutionary process driven by requirements to minimize corrosion and erosion in the cooling system, ensure material compatibilities, and minimize maintenance requirements. While the bases of most contemporary antifreezes are propylene glycol or ethylene glycol, the additive packages vary considerably, which can lead to confusion and severe maintenance problems if not properly understood and executed. It is the additive package that differentiates the various categories and classifications of antifreeze. TABLE 11-3 outlines the most common maintenance demands placed on antifreeze additive packages needed to produce a properly formulated coolant.

1.1. Type I: Conventional Low-Silicate Antifreeze

Type I: Conventional Low-Silicate Antifreeze To protect cooling system materials, such as cast iron, aluminum, copper, brass, solder, steel, and many non-metallics like nylon and silicone, antifreeze contains corrosion inhibitors. Type I conventional antifreeze uses older additive technology and contains corrosion inhibitors such as boron, phosphate, and sodium silicate TABLE 11-4. These types of inhibitors are known as IAT and are identified by the green-colored coolant. Sodium silicate is primarily used to protect aluminum and is found in much higher concentration when used in gasoline engines with aluminum cylinder heads. A problem with sodium silicate in diesels, however, is its incompatibility with high levels of nitrite, which is added to antifreeze to protect cylinder walls from cavitation erosion. High concentration of both of these additives together will cause a condition known as silicate dropout Figure 33. Silicate dropout is characterized by the appearance of green “goo” or gel that plugs radiator and heater core tubes, leading to loss of adequate cab heat, overheating of the engine, and even catastrophic engine failure. For this reason, type I antifreeze is blended differently for gasoline and diesel engines, with much more silicate blended into gasoline engine antifreeze.

FIGURE 11-33: Silicate dropout forms a green, gooey substance in the cooling system that blocks coolant tubes in radiators and heater cores.

Type I additives deplete quickly and require monitoring. With time, many of the additive’s other components, such as phosphorous, drop out with the silicate, coating cooling system components with a layer of slime and mineral deposits. This is why it is important to drain and replace type I antifreeze containing this corrosion-inhibitor package every 2 years. To maintain the correct level of additives, type I coolant requires testing to ensure that the correct levels of nitrite and other inhibitors are also present.

Between 3–5% of DCA or SCA is added to type I antifreeze after the initial mixing of antifreeze and water to bring the additive package for diesel engines to the correct protection level Figure 34. Monitoring of the additive package using test strips is necessary at every service to maintain the correct levels of the various corrosion inhibitors Figure 35 and Figure 36.

FIGURE 11-34: This bottle of liquid additive is added to approximately 1 gallon (4 liter) of type I coolant to properly condition the coolant. Note the dried silicate around the cap of the bottle.

FIGURE 11-35: Test strips are used to measure the levels of various cooling system additives. This test strip measures the levels of nitrite and molybdates, another type of corrosion inhibitor, in antifreeze.

FIGURE 11-36: This test strip checks the nitrite levels in either type I coolant or ELC. A different scale located on the side of the bottle is used for each type of antifreeze.

1.2. Extended-Life Coolant

Extended-Life Coolant Given the high maintenance requirements of type I antifreeze and its short 2-year service interval, manufacturers have sought to develop new coolant technology to minimize cooling system maintenance and extend the service interval. To achieve this, a new category of antifreezes, called extended-life coolant (ELC) or LLC , have been developed with corrosion inhibitors made from organic acids. TMC classifies these coolants as types II–IV. Types II–VI coolants use OAT additives, which do not deplete in use. The other type of additive package used by ELC’s type V and VI is nitrited/nitrated organic acid technology (NOAT). Generally, OAT and NOAT coolants do not require an initial charge of DCA or SCA because they are fully formulated. This means any required additives are incorporated into the antifreeze–inhibitor solution during manufacture TABLE 11-5. The corrosion inhibitors in these types of ELC antifreezes are designed to last 600,000 miles (965,600 kilometre [km]) on-road or 12,000 hours off-road. However, a coolant extender that contains nitrite for protection against cavitation erosion may be added Figure 37. This must be added only once at 300,000 miles (482,800 km) or 6000 hours, which is about halfway through the antifreeze’s service life, if a longer service life is expected.

FIGURE 11-37: The use of an extender additive package halfway through an ELC’s service life can lengthen the time that LLC remains in service.

Compared to antifreeze with IATs, OAT antifreeze has the advantage of being more chemically stable, which allows for exceptionally long service intervals. OAT uses carboxylate acids, which are neutralized versions of acids containing carbon. OAT is free of nitrite, nitrate, phosphate, silicate, and borate corrosion inhibitors. The formulation provides maximum protection of the six basic metal alloys found in most cooling systems. Because the OAT coolant generally contains no phosphates or silicates, deposits in the cooling system are almost eliminated. Without the IAT additives that can form into abrasive solids that are dissolved in antifreeze, the use of OAT results in improved water pump seal and impeller life.

1.3. Universal Hybrid Organic Acid Technology Antifreeze

Universal Hybrid Organic Acid Technology Antifreeze
Hybrid organic acid technology (HOAT) is another category of long-life, fully formulated antifreeze that is a combination of some of the inhibitors used in IAT and nitrite/nitrate. This makes HOAT compatible with both light-duty (LD) and HD diesel cooling system materials. Different versions of this anti freeze are dyed colors ranging from orange to straw yellow. Adding nitrite into OAT to prevent cavitation erosion during production is intended to allow marketers to classify HOAT as a universal antifreeze that is useable in all cooling systems. Many engine OEMs do recommend HOAT for a system fill because HOAT uses additives found in conventional IAT, such as nitrite/nitrate, which can be depleted during engine use. The result is that the HOAT additive package must be tested and topped off with an SCA intended for HOAT antifreeze in order to maintain effective cavitation and corrosion protection.

1.4. Nitrated and Nitrite/Nitrate Organic Acid Technology

Nitrated and Nitrite/Nitrate Organic Acid Technology
Nitrite/nitrate organic acid technology (NOAT) is similar to HOAT but with additional amounts of nitrates/nitrites added. This chemical combination is expected to make the antifreeze suitable for use in both LD and HD diesel cooling systems, and it is also marketed as a universal antifreeze. NOAT and HOAT are very similar in performance characteristics, but currently no vehicle OEM uses a factory fill of NOAT antifreeze. The normal NOAT service life is 5 years or 150,000 miles (250,000 km) and uses an extender package halfway through the service life.

NOAT is a desirable antifreeze chemistry undergoing refinement to rid the formulation of the aluminum-damaging nitrites and nitrate additives. This coolant chemistry is the only one that is considered to never require draining. Additionally, neither top offs nor testing are required with its use.

1.5. Maintaining Types II and III Fully Formulated Antifreeze

Maintaining Types II and III Fully Formulated Antifreeze

When antifreeze is retailed as fully formulated, it contains a pre-charge of any required SCA/DCA additive package. To maintain these fully formulated antifreezes at every preventive maintenance service—or at least twice per year—the color and freeze point of the coolant are checked. If the coolant is the correct color, has no deposits, and has a freeze point between −15° F (−26° C) and −60° F (−51° C), then the coolant is considered to be in suitable condition for further use.

Mixing IAT with OAT, HOAT, and NOAT antifreezes will not damage the engine’s cooling system. However, mixing antifreezes nullifies the extended-life attributes of these formulations. Depending on the type of formulation, acceptable contamination can range from 5–25%, though most OEMs do not recommend allowing contamination to exceed 5%.

It is easy to be confused with the variety and complexity of antifreeze formulations available for use. Therefore, it is imperative that the technician and diesel engine owner be fully aware of and carefully follow the vehicle manufacturer’s requirements and recommendations for antifreeze.