Automotive Systems

Formerly Automotive Systems I

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In the cooling system, the radiator is a heat exchanger that removes the heat from the coolant passing through it. The radiator holds a large volume of coolant in close contact with a large volume of air so heat will transfer from the coolant to the air. The components of a radiator are as follows:

  • CORE—The center section of the radiator made up of tubes and cooling fins.
  • TANKS—The metal or plastic ends that fit over core tube ends to provide storage for coolant and fittings for the hoses.
  • FILLER NECK—The opening for adding coolant. It also holds the radiator cap and overflow tube.
  • OIL COOLER—The inner tank for cooling automatic transmission or transaxle fluid.
  • PETCOCK—The fitting on the bottom tank for draining coolant.

A tube-and-fin radiator consists of a series of tubes extending from top to bottom or from side to side (fig. 6-5). The tubes run from the inlet tank to the outlet tank.

Fins are placed around the outside of the tubes to improve heat transfer. Air passes between the fins. As the air passes by, it absorbs heat from the coolant. In a typical radiator, there are five fins per inch Radiators used in vehicles that have air conditioning have seven fins per inch. This design provides the additional cooling surface required to handle the added heat load imposed by the air conditioner.

Radiators are classified according to the direction that the coolant flows through them. The two types of radiators are the downflow and crossflow.

  • The downflow radiator has the coolant tanks on the top and bottom and the core tubes run vertically. Hot coolant from the engine enters the top tank. The coolant flows downward through the core tubes. After cooling, coolant flows out the bottom tank and back into the engine.
  • The crossflow radiator is a design that has the tanks on the sides of the core. The core tubes are arranged for horizontal coolant flow. The tank with the radiator cap is normally the outer tank.
  • A crossflow radiator can be shorter, allowing for a lower vehicle hood.

The operation of a radiator is as follows: The upper tank collects incoming coolant and, through the use of an internal baffle, distributes it across the top of the core.

  • The core is made up of numerous rows of small vertical tubes that connect the upper tank and the lower tank. Sandwiched between the rows of tubes are thin sheet metal fins. As the coolant passes through the tubes to the lower tank, the fins conduct the heat away from it and dissipate this heat into the atmosphere. The dissipation of the heat from the fins is aided by directing a constant air flow between the tube and over the fins.
  • The lower tank collects the coolant from the core and discharges it to the engine through the outlet pipe.
  • The overflow tube provides an opening from the radiator for escape of coolant if the pressure in the system exceeds the regulated maximum.This will prevent rupture of cooling system components.

A transmission oil cooler is often placed in the radiator on vehicles with automatic transmissions. It is a small tank enclosed in one of the main radiator tanks.

Since the transmission fluid is hotter than engine coolant, heat is removed from the fluid as it passes through the radiator and cooler.

In downflow radiators, the transmission oil cooler is located in the lower tank. In a crossflow radiator, it is located in the tank having the radiator cap. Both tanks are coolant outlet tanks.

Line fittings from the cooler extend through the radiator tank to the outside. Metal lines from the automatic transmission connect to these fittings. The transmission oil pump forces the fluid through the lines and cooler.

Figure 6-5.—Engine radiator construction.
Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

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