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

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.