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.

Radiator Hoses

Radiator hoses carry coolant between the engine water jackets and the radiator. Being flexible, hoses can withstand the vibration and rocking of the engine without breaking.

The upper radiator hose normally connects to the thermostat housing on the intake manifold or cylinder head. The other end of the hose fits on the radiator. The lower hose connects the water pump inlet and the radiator.

A molded hose is manufactured into a special shape with bends to clean the parts especially the cooling fan. It must be purchased to fit the exact year and make of the vehicle.

A flexible hose has an accordion shape and can be bent to different angles. The pleated construction allows the hose to bend without collapsing and blocking coolant flow. It is also known as a universal type radiator hose.

A hose spring is used in the lower radiator hose to prevent its collapse. The lower hose is exposed to suction from the water pump. The spring assures that the inner lining of the hose does NOT tear away, close up, and stop circulation.

Radiator Pressure Cap

The radiator pressure cap (fig. 6-6) is used on nearly all of the modern engines. The radiator cap locks onto the radiator tank filler neck Rubber or metal seals make the cap-to-neck joint airtight. The functions of the pressure cap are as follows:

1. Seals the top of the radiator tiller neck to prevent leakage.

2. Pressurizes system to raise boiling point of coolant.

3. Relieves excess pressure to protect against system damage.

4. In a closed system, it allows coolant flow into and from the coolant reservoir.

The radiator cap pressure valve consists of a spring- loaded disc that contacts the filler neck. The spring pushes the valve into the neck to form a seal. Under