Cooling systems

The function of the cooling system is to maintain the temperature of the engine at that temperature which the engineers have found advisable and for which they designed the engine. Any variation to any extent above or below this optimum temperature invites trouble and early engine deterioration [24]. There are two types of liquid cooling systems based on the forces that circulate the coolant [25]. These two types are the gravity [26], natural, or thermosiphon system and the pump or forced system.

The forced type of circulation is the predominating method of circulating the liquid coolant: A centrifugal [27] type of pump is used, its pressure depending on its size and the speed of operation. This type of pump is used because, if the regular channels of circulation are cut off by thermostats, the pump merely circulates the water within the pump housing with no damage to the part and no build up of high pressures within the system. A centrifugal pump draws liquid in at the center and throws it to an outlet [28] by the spinning effect of the rapidly rotating blades [29].

The pump is usually driven by the same shaft that supports the fan as the fan rotates, so does the water pump. Ball bearings are being used in these pumps so that they can be lubricated for life and, therefore, offer little maintenance problems. Others have bushed bearings and utilize grease [30] or oil. Spring-loaded [31] fiber, rubber [32], or leather seals [33] keep the lubricant and coolant separated. Important parts of the engine cooling system are the pump, the fan [34], radiator, shutters [35], thermostat, hose belts, and gages or indicators.

Pumps of the centrifugal types are found in the forced circulation system. They may pump anywhere from 15 to 50 gpm (gallons per minute). Systems using high-capacity pumps will usually use less coolant, and they will, therefore, have a quick warmup [36] period as there is less coolant to heat.

The fans are necessary in order to move a large volume of air. This is true where the engine is air-cooled or if it is liquid-and-air-cooled.

Gages [37] or indicators indicate the approximate temperature of the coolant.

The most common radiator type has the coolant flowing from top to bottom through round or flattened [38] tubing. The flattened tubing has more flexibility in case the coolant freezes and hence will not burst as easily.

The reader may come across the term heat exchanger. The tractor radiator is one form of heat exchanger [39], merely serving as a device for the transfer or exchange of heat from the liquid to the gaseous air.

The purpose of the cooling system is to control the temperature of the engine within reasonable limits while operating, and to assist in the rapid warmup of the engine so as to decrease wear and to arrive quickly at an efficient operating temperature. To accomplish this purpose, tractor and automobile engines have been equipped with shutters or thermostats, sometimes both. The cooling system using air entirely as the outside coolant requires very little attention, perhaps just enough to see if all the passages are free.

The engine using the liquid-air combination does require considerable attention. It is just as important to keep the cooling system clean and free from obstructions as it is the lubrication system. The three greatest “saboteurs” of the cooling system are rust [40], scale [41], and electrolysis [42].