Cooling systems are provided on all types of gasoline engines. As the heat generated by the constant explosions in the cylinders would soon overheat and ruin the engine were it not cooled by some artificial means.

Circulation Systems.—There are two types of water circulating systems. The Thermo Syphon, and the Force Pump circulating systems.

Fig. 47 shows how the water circulates in the Thermo-Syphon system. It acts on the principle that hot water seeks a higher level than cold water, consequently when the water reaches a certain temperature, approximately 180° F., circulation commences and the water flows from the lowest radiator outlet pipe up through the water jackets into the upper radiator water tank, and down through the thin tubes to the lower tank to repeat the process.

The heat is extracted from the water by its passage through the thin metal tubing of the radiator to which are attached scientifically worked out fins which assist in the rapid radiation of the heat. The fan just back of the radiator sucks the air through the small tubes which connect the upper and lower radiator tanks. The air is also driven through between these tubes by the forward movement of the car.

The Force Pump Circulation System.—The Force Pump circulating system is constructed in the same manner as the Thermo Syphon Cooling System. The only difference in the two systems is that a small pump is attached to the lower radiator pipe to force the circulation of the water.

The pump is usually of the centrifugal type and consists of a fan-shaped wheel operated in a snugly fitted housing. The water enters at the hub and is thrown out against the housing and is forced on by the rapid action of the fan blades. Another type of pump is used by some manufacturers which consist of two meshed gears of the same size, which operate in a snugly fitted housing. These gears operate in a direction toward each other, the water is carried forward or upward in the space between the teeth, and is forced on when the teeth mesh and fill the space.

Overheating.—Overheating may be caused by carbonized cylinders, too much driving on low speed, not enough or a poor grade of lubricating oil, spark retarded too far, racing the engine, clogged muffler, poor carburetor adjustment, a broken or slipping fan belt, jammed radiator tube, leaky connection, or low water.

Radiator Cleaning.—The entire circulation system should be thoroughly cleaned occasionally. A good cleaning solution is made by dissolving one-half pound of baking soda in three and one-half to four gallons of soft water. The radiator is filled with the solution and left to stand for twenty to thirty minutes. The hose is then removed from the lower pipe, water is then turned into the radiator through the filler spout until the system is thoroughly flushed out.

Freezing.—Unless an anti-freezing solution is used through the cold months you are bound to experience trouble. The circulation does not commence properly until the water becomes heated. It is apt to freeze at low temperatures before circulation commences. In case any of the small tubes are plugged or jammed they are bound to freeze and burst open if the driver attempts to get along without a non-freezing solution.

Freezing Solution.—Wood or denatured alcohol can be used to a good advantage. The following table gives the freezing point of solutions containing different percentages of alcohol.

A solution composed of 60% of water, 10% of glycerine, and 30% of alcohol is commonly used, its freezing point being 8° below zero.

Evaporation.—On account of evaporation, fresh alcohol must be added frequently in order to maintain the proper solution.

Radiator Repairs.—A small leak may be temporarily repaired by applying brown soap, or white lead, but the repair should be made permanent with solder as soon as possible. A jammed radiator tube is a more serious affair. While the stopping up of one tube does not seriously interfere with circulation, it is bound to cause trouble sooner or later, and the tube will freeze in cold weather. Cut the tube an inch above and below the jam and insert a new piece soldering the connection. If the entire radiator is badly jammed or broken, it will probably be advisable to install a new one.

Air Cooling System.—Air cooling has been developed to a point where fairly good results are attained. This system has an advantage over the circulating systems, in that the weight of the radiator and water is done away with, and no trouble is experienced with stoppage of circulation and leaky connection. This system, however, has its drawbacks, in that it cannot be used successfully on the larger and more compact engines. In order to allow the necessary large space for radiation, the cylinders are heavily flanged and set separately. The fan is placed in a much higher position than usual, in order that the air current may strike the heads of the cylinders and circulate downward. Compression is also lowered considerably to prevent heat generation and pre-ignition. On account of the small size of the cylinders and low compression, it is necessary to operate an air cooled engine at a very high rate of speed to produce sufficient power for automobile locomotion.

The fan must be kept in good working condition, and care should be exercised in not allowing the engine to run idle for any length of time.