LO 11-4 Classify and describe the types, functions, and applications of diesel engine coolant

1. Classifications of Coolant

Classifications of Coolant

HD and automotive diesel engines depend almost exclusively on the efficiency of liquid cooling systems. Water mixed with antifreeze and additives, called conditioners , is referred to as coolant in some regions and is the medium used to absorb engine heat. A heat exchanger (e.g., a radiator) transfers heat from the coolant to the atmosphere. However, when examining antifreeze alone as a system component, it is important to understand that not all engine coolants are the same or interchangeable. For example, the antifreeze used in diesel engines versus gasoline engines is different and almost never interchangeable. Extensive use of aluminum in SI engines and the requirement for additives to prevent cavitation erosion in diesels demand very different additive packages that are blended together in what is called fully formulated antifreeze . Four factors have led to the development of six classifications of engine antifreeze, but only types I–IV are currently recognized by the American Trucking Associations’ Technology & Maintenance Council (TMC), an industry group that recommends service practices for commercial vehicles TABLE 11-2. These factors include:

1. Different ratios of metals and the composition of materials used to manufacture cylinder blocks and heads: The amount of aluminum, copper, iron, brass, and solder used in radiators and other components varies greatly between SI engines and diesel engines and even more so between manufacturers. All these metals require different additive packages to adequately protect against the corrosion of components in contact with coolant. Not all antifreeze packages contain the correct additives in the proper concentrations, even when the producer formulates an antifreeze with all the appropriate additives. In other words, there is no such thing as a universal antifreeze.

2. Material compatibility of additives with cooling system materials: Hoses, gaskets, and seals in contact with coolant may have adverse chemical reactions with the coolant chemistry. Days, weeks, or month after the wrong coolant is used, head gaskets may suddenly fail, or coolant hoses may burst. For example, over time, certain types of common elastomers used in silicone hoses that are widely installed in commercial vehicles will soften and degrade as a result of contact with coolant-containing OAT. Additionally, OAT coolants are very harsh on some plastic materials used in gaskets.

3. The development of extended-life antifreeze: Today, several varieties of coolant are produced to reduce maintenance requirements and extend coolant drain intervals. Each of these extended- or long-life antifreezes contains very different sets of corrosion inhibitors to protect metal exposed to the coolant. Several very different types of extended-life coolant (ELC) are produced, each uniquely formulated with additives compatible with materials exposed to coolant. Note again that the use of a coolant with an additive package that is acceptable in one engine may lead to failure of parts in contact with coolant in another engine.

4. Introduction of non- or low-toxic environmentally friendly antifreeze bases: To reduce the costs associated with waste coolant disposal and the environmental footprint of commercial vehicles, as well as to minimize animal poisoning, less toxic antifreeze is used as a factory fill or made available as a service replacement. Currently, the three major types of antifreeze bases to which an additive package is added are as follows:

• Ethylene glycol (toxic)
• Propylene glycol (low toxicity)
• Glycerin (nontoxic)

Notwithstanding coolant manufacturer claims, no single universal coolant is made that is interchangeable or compatible with other coolants and all materials composing engine gaskets, hoses, engine castings, and synthetic materials. The next sections presented in this chapter will examine the types of antifreeze and ingredients used to manufacture and maintain important coolant properties. Classifying and understanding coolant additive packages will provide the background information needed to make correct recommendations and to develop proper maintenance practices associated with the cooling system.   Technicians Tip     In spite of claims by marketers, there is no such thing as a universal engine coolant. Antifreeze, also called coolant , is formulated differently for SI engines than for diesels. The extensive use of aluminum in SI engines rather than iron, as used mostly in diesels, requires a different additive package to prevent metal corrosion and cavitation erosion. OEM-specific additive packages, or the absence of a critical additive in antifreeze, may cause rapid deterioration and destruction of some cooling system materials, such as gaskets, hoses, and seals. It is critically important that technicians top off or replace engine coolant using only the OEM-recommended antifreeze. Doing otherwise risks both long- and short-term damage to an engine and system components Figure 26.

FIGURE 11-26: Red-colored ELC formulated with OAT corrosion inhibitors is the most popular choice of antifreeze for North American diesel engine manufacturers, such as Cummins.

1.1. Water and Coolant

Water and Coolant

Some engines are air cooled; they are used primarily in off-road, agricultural, mining, and heavy-equipment applications. Deutz is one popular European manufacturer of air-cooled diesel engines that dispenses with the maintenance involved in using liquid coolant Figure 27. However, outside of Deutz, cooling systems circulating liquid coolants are exclusively used by OEMs because they enable the use of high-power output engines with long service life. Water is mixed into engine coolant because it is the most efficient fluid to transfer heat. Compared to air, oil, or other liquids, water can quickly absorb and release heat better than any other liquid. However, while using water alone as an engine’s only coolant seems efficient, it is detrimental to engine operation. Water can not only freeze and crack engine castings but also quickly corrode the engine internally. Adding antifreeze containing corrosion inhibitors to water can eliminate these problems and extend engine life while simultaneously providing the benefit of increasing the boiling temperature of the coolant. Additionally, new antifreeze formulations have dramatically improved the ability of antifreeze to perform its basic functions while reducing the cooling system’s maintenance requirements, maintenance costs, and impact on the environment related to the disposal of used coolant. Water alone in a cooling system causes the corrosion of metal parts and therefore requires the addition of corrosion inhibitors.

FIGURE 11-27: The large fan on this industrial Deutz engine is used to circulate air over cylinder cooling fins.

FIGURE 11-28: A surge tank in a school bus filled with ELC. Note that premixed coolant with a 50/50 water-to-antifreeze mixture is recommended.

Distilled water, used in premixed coolant, is best used in cooling systems because it has no mineral content to scale, or deposit, on the cooling system surface. Chlorine, which forms corrosive chloride chemical compounds, is also absent from distilled water. The percentage of antifreeze in the water mixture should never be higher than 60% or lower than 40%. Coolant with less than 40% concentration of antifreeze may not contain enough corrosion inhibitors. Concentrations over 65% will not permit the coolant to remove heat effectively and will in fact lose its freeze-protection properties. A 50/50 mixture is optimal for removing heat and providing corrosion protection Figure 28. However, extremely cold operating conditions may demand a higher concentration of antifreeze. Similarly, a higher concentration of water than antifreeze in extreme heat conditions improves heat transfer. In hot climates, a concentration of less than 40/60 is not recommended because, again, insufficient quantities of additives are present to protect the cooling system. For boil protection, antifreeze concentrations in engines operating above 195° F (91° C) should not be less than 50%.

To prevent antifreeze and water from producing foam as it circulates, antifoaming additives are used. Bubbles do not transfer heat well and should be eliminated. These additives lower the surface tension of vapor bubbles to prevent the formation of large bubbles.

It is important to remember that too high a concentration of antifreeze will reduce the ability of coolant to absorb and release heat. An antifreeze/water preparation is capable of absorbing and releasing as much as 50–70% less heat than pure water. Lowering what is called the coolant’s specific heat properties by diluting water with excess antifreeze leads to poor engine cooling, overheating, and inadequate passenger compartment heating. Overconcentrating antifreeze not only results in the loss of passenger compartment heating but also engine overheating because the coolant’s ability to release heat is also diminished. Note that two major categories of antifreeze bases require different concentrations to provide the same freeze protection. Propylene glycol–based antifreeze, a safer nontoxic or low- toxicity antifreeze base, requires higher concentration to achieve the same freeze protection as ethylene glycol–based antifreeze.

1.2. Coolant pH

Coolant pH One major factor affecting the corrosion rate of the metals in an engine is the coolant’s pH level—that is, its alkaline or acidic chemical property. A material’s pH is measured on a scale of 0–14, with 7 being neutral. A coolant with a pH less than 7 is acidic, and a coolant with a pH more than 7 is alkaline. Coolant pH should be maintained between 8.5 and 10.5. Shifts in coolant pH affect the rate of corrosion of different metals Figure 29. If a coolant’s pH drops below 8.5, it becomes aggressive to ferrous metals (e.g., cast iron and steel), aluminum, copper, and brass. If it increases above 11, it becomes aggressive to aluminum and solder. Maintaining optimum pH in a coolant is a critical function of a supplemental coolant additive package that also contains DCA or SCA. Ethylene glycol antifreeze can become more acidic over time when exposed to air. Combustion gas leakage into coolant can also make it acidic. Overconcentration and overuse of a conditioner that contains pH buffers to make coolant alkaline cause coolant to become destructive to engine metal as well.

FIGURE 11-29: Depending on the coolant’s pH level, it can become corrosive to different types of metals.

1.3. Ethylene Glycol Antifreeze Base

Ethylene Glycol Antifreeze Base

Coolant has evolved considerably since the early days of automotive technology. In the past, coolant included mixtures of alcohol and water as well as water mixed with honey and soluble oils. In the 1940s, ethylene glycol was developed to provide both freeze and boil-over protection. When initially manufactured, ethylene glycol is a clear, colorless, syrupy fluid. Green dye is added for identification. One of the most significant reasons ethylene glycol is dyed is to clearly distinguish it from other coolants, as it is extremely poisonous. If ingested, 4 oz (113 g) of ethylene glycol will cause fatal kidney failure in humans after a couple of days. Many animals die from antifreeze poisoning every year because they are attracted to the antifreeze’s sweet odor and taste. Embitterment may be added to antifreeze by some producers to discourage animals from drinking antifreeze leaking from engines. Ethylene glycol–based coolants must be recovered and recycled to prevent environmental contamination. TMC categories for ethylene glycol are types I, II, and IV. Types V and VI are not designated as having any specific type of antifreeze base.

1.4. Propylene Glycol

Propylene Glycol To minimize the problems associated with the toxicity of ethylene glycol, an environmentally friendly antifreeze base called propylene glycol is available for diesel engine cooling systems. Propylene glycol is an ingredient in many cosmetics and foods, from moisturizer to ice cream. It has slightly different physical properties than ethylene glycol; therefore, the density and concentration required for freeze protection is different. This explains why it is important to differentiate between ethylene glycol and propylene glycol antifreeze bases as well as the amount of propylene glycol mixed with water to obtain adequate freeze protection Figure 30. The color of antifreeze is probably the most reliable indication of the type of antifreeze base. TMC classifies propylene glycol–based antifreeze as a type III and has recommended that antifreeze producers color propylene glycol antifreeze blue. A higher concentration of propylene glycol is required to provide the same freeze protection achieved using ethylene glycol. Higher concentrations may reduce the cooling effectiveness of propylene glycol mixtures. The slippery, greasy texture of both ethylene glycol and propylene glycol antifreeze bases makes both an excellent lubricant for the water pump seal.

FIGURE 11-30: A refractometer screen has two different scales for measuring the freeze protection of propylene glycol and ethylene glycol coolants.

1.5. Glycerin-Based Antifreeze

Glycerin-Based Antifreeze
Glycerin is another nontoxic base for antifreeze. Glycerin was used as a heat transfer agent in antifreeze formulations as early as the 1920s but was eventually displaced by ethylene glycol. Interest in this antifreeze base has been revived due to the biofuel industry, which produces huge amounts of glycerin as a byproduct of biofuel production. Glycerin, which is also sometimes called propanetriol or glycerol , has a number of distinct advantages, including:

• Close to neutral pH
• Inexpensive, or at least cost-competitive, price point
• Environmentally friendly, nontoxic properties
• Support of the renewable fuel industry
• Compatibility with most cooling system material

Cummins currently produces a glycerin-based antifreeze, Compleat™, that meets the recently developed ASTM International (formerly known as the American Society for Testing Materials) standard for the latest antifreeze technology. There is currently no TMC designation for this type of antifreeze.

The primary disadvantage of glycerin is that its freeze- protection temperature is high in comparison to that of ethylene glycol. Diluted to a 30/70 water-to-glycerin concentration, glycerin can provide freeze protection only to −36° F (−37.8° C). At that concentration and freeze-protection point, glycerin-based coolant is not able to remove as much heat as a mixture with a higher amount of water and the same freeze protection. The different density of the antifreeze also requires new test instruments, such as a purpose-made refractometer, to evaluate freeze protection. Test strips presently used for the evaluation of glycol-based coolant conditions in service are not usable for glycerin-based coolants.

FIGURE 11-31: Note that this coolant is not blue but contains purple type II antifreeze with organic acid technology additives but no phosphate. Both Detroit Diesel and other European engine manufacturers do not want dissolved solids, such as phosphates, in their engine coolant.

FIGURE 11-32: This Kenworth truck chassis, with an electric drive propulsion system, has a fuel cell. It is critical that only the correct coolant and distilled or deionized water is added to the cooling system.