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LO 11-6 Identify and describe the construction features, types, and applications of the diesel engine cooling components

1. Components of Cooling Systems

1.1. Radiators

LO 11-06: Identify and describe the construction features, types, and applications of the diesel engine cooling components.

 

Radiators

The radiator is a highly visible cooling system component. Radiators are designed and used to accommodate various heat transfer requirements and chassis applications. Radiator technology continues to change to extend service life and operate more efficiently while reducing construction costs and maintenance requirements.

Radiators are heat-exchanging devices that release the heat absorbed by the coolant circulating around the engine into the air. Coolant can flow through a radiator in two ways. In downflow radiators, the coolant enters through a large hose connected to the top tank of the radiator that carries hot coolant from the thermostat outlet. The coolant then flows downward from the top tank, travels through cooling tubes, and enters the bottom radiator tank at a cooled temperature. Alternatively, in cross flow radiators, coolant flows from a thermostat outlet to a top hose connected to a side-mounted radiator tank. Coolant then flows across cooling tubes in the radiator to another side-mounted tank Figure 38. Cross flow radiators are preferred in vehicles with low-profile, aerodynamic hoods because they can be made wider with a lower height profile. Downflow radiators have a taller but narrower profile that can fit between frame rails Figure 39.

Tubes within the radiator core provide the surface area needed to exchange heat. Heat dissipates from the coolant through the tube wall and then through the fins. Air passing through the fins carries away the heat, thereby allowing tubes and fins to absorb more heat from the coolant Figure 40.

Fig11_38

FIGURE 11-38: A. Downflow radiator. B. Cross flow radiator.

   Fig11_39

FIGURE 11-39: A narrower downflow tank with a replaceable core for a premium-quality vehicle. This is a four-core radiator.

   Fig11_40

FIGURE 11-40: Tube and fin construction of a radiator.

 

Copper Versus Aluminum Radiator Material
Early radiator construction used copper brass radiator components. Copper brass construction seemed to be the obvious choice for radiators because of its superior heat conductivity, ease of forming, and repair. However, it was learned that increasing the diameter of the tubes in a radiator made radiators more efficient, lighter, and compact. This required thicker tube walls to prevent ballooning of the tubes from internal pressure; the increased weight created unacceptably heavier radiators. Beginning in the 1980s, most manufacturers started to use aluminum tube radiators Figure 41. A two-row aluminum radiator core (also referred to as a double core radiator ) with 1" (25 mm) circumference tubes is equivalent to a five-row, copper brass radiator with 1/2" (13 mm) circumference tubes. The 1" (25 mm) tube size also improves tube-to-fin contact in addition to increasing cooling system capacity by roughly 25%.

Copper is a good heat conductor, but the lead solder required to bond the tubes to the fins creates an insulation point that prevents some heat transfer. All the mechanical stresses are borne by the solder in the joints between the radiator tank and the tube core that can weaken and leak over time. Solder can be attacked if the coolant pH level becomes too alkaline through the overuse of DCA or SCA. Aluminum tubes are instead welded or crimped, rather than soldered, to either aluminum or plastic radiator tanks. This inexpensive arrangement provides a more efficient conductor for cooling.

Radiator cores are replaceable, and the radiator tanks are reusable in both the aluminum and the brass tube-type designs. However, inexpensive aluminum radiators are usually replaced as a complete unit.

   Fig11_41

FIGURE 11-41: This radiator is a common design in which plastic tanks are crimped to an aluminum cooling core. A silicone gasket between the tank and the radiator core prevents leaks.

 

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