ENGINE COOLING SYSTEMS

All internal combustion engines are equipped with some type of cooling system because of the high temperatures they generate during operation. The temperature in the combustion chamber during the burning of fuel is much higher than the melting point of iron. Therefore, if nothing is available to cool the engine during operation, valves burn and warp, lubricating oil breaks down, and bearings and pistons overheat resulting in engine seizure. At the same time, the engine must not be allowed to run too cold. An engine running cold does not burn all the fuel taken into the combustion chamber, causing carbon deposits to form that reduce fuel mileage, increase wear, and reduce engine power.

Three functions of the cooling system provide a satisfactory temperature operating range for the engine. First, the system removes the unwanted heat. Second, it regulates the engine temperature to keep it just right during all operating conditions. Third, when the engine is first started, the cooling system assists the engine in warming up to its normal operating temperature as soon as possible.

The two types of cooling methods are liquid cooling and air cooling. The liquid-cooling system is the most popular for automotive use, because it provides the most positive cooling and it maintains an even engine temperature. Air cooling is used for small vehicles and equipment; however, air cooling is not used if water cooling is practical. This is because air-cooled engines do not run at even temperatures and require extensive use of aluminum to dissipate heat. Other means of heat dissipation for the engine, in addition to the cooling system, are as follows: . The exhaust system dissipates as much, if not more, heat than the cooling system, although that is not its purpose.

l The engine oil removes heat from the engine and dissipates it to the air from the sump.

. The fuel provides some engine cooling through vaporization.

. A measurable amount of heat is dissipated as the air passes over the engine.

LIQUID-COOLING SYSTEM

A simple liquid-cooled cooling system consists of a radiator, water pump, hoses, fan and shroud, thermostat, and a system of jackets and passages in the cylinder head and cylinder block through which the coolant circulates (fig. 1-44). Cooling of the engine parts is accomplished by keeping the coolant circulating and in contact with the metal surfaces to be cooled. The pump draws the coolant from the bottom of the radiator, forces it through the jackets and passages, and ejects it into the upper tank on top of the radiator. The coolant then passes through a set of tubes to the bottom of the radiator from which the cooling cycle begins again. The radiator is situated in front of a fan that is driven either by the water pump or an electric motor. The fan ensures an air flow through the radiator at times when there is no vehicle motion.

Radiator

Most radiators have two tanks with a heat exchanging core between them. The upper tank contains an outside pipe, called an inlet, and on top is the filler neck. Attached to the filler neck is an outlet to the overflow pipe. The overflow pipe provides an opening from the radiator for escape of coolant or steam if pressure in the system exceeds the regulated maximum. This prevents rupture of cooling system components. The lower tank contains an outside pipe that serves as the outlet for the radiator.

The radiator is usually mounted in the front of the engine compartment so cool air can pass freely through the core. The outlet on the bottom radiator tank is connected to the water pump inlet. The top tank inlet of the radiator is connected to the outlet at the top of the engine. Rubber hoses and hose clamps are used to make

Figure 1-44.-Liquid-cooling system.

these connections to prevent engine vibrations from being transferred to the radiator.

When performing prestart checks on the radiator system, check for leaks, particularly where the tanks are soldered to the core, because vibration and pulsation from pressure can cause fatigue of soldered joints or seams. Bent fins should be straightened and the radiator core checked for any obstructions, tending to restrict the air flow. Radiator air passages can be cleaned by blowing them out with an air hose in the direction opposite to the ordinary flow of air. Water can also be used to soften obstructions before applying the air blast. In any event, the cleaning gets rid of dirt, bugs, leaves, straw, and other debris that would otherwise clog the radiator and reduce its cooling efficiency.

CAUTION

Spraying high-pressure water to soften an obstruction on the radiator can cause damage to the fins and core.

All hoses and tubing should be checked for leakage and general condition. The leakage may often be corrected by tightening or replacing the hose clamps.

Deteriorated hoses should be replaced to preclude future troubles; for example, hoses sometimes rot on the inside, allowing tiny fragments to flow through the system and become lodged in the radiator, tending to clog it and cause overheating. For this reason, all old, cracked, or spongy hose should be replaced as soon as the condition is discovered during the prestart checks.