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.