Problems with the cooling system of an engine may prevent the cooling system from keeping the engine parts and working fluids at safe operating temperatures. Failure of the system may lead to several of the troubles and casualties that have been discussed earlier.

In marine installations, lubricating oil and most of the engine parts are cooled by the circula-tion of seawater, freshwater, or both. When the cooling of an engine part is mostly by oil spray or oil circulation, the oil is cooled by circulation through an oil cooler. Figure 3-11 illustrates a cooling system in which both freshwater and seawater serve as coolants.

When maintaining engine cooling water temperatures within specified limits, the principal difficulties you may encounter are in maintain-ing circulating pumps in operating condition; preventing corrosion; reducing the cause of scale formation in water jackets and heat exchangers; cleaning jackets and heat exchangers according to proper procedures; and in preventing leaks in the various parts of the system.

The coolers (or heat exchangers) which remove the heat from the cooling water of an engine may vary considerably in design. Those used in cool-ing systems may be classified basically as the radiator type and the tubular type. The radiator is sometimes referred to as the strut or the Har-rison type, while the tubular is identified as the Ross or shell-and-tube type. A heat exchanger of both types is shown in figure 3-12. The heat ex-changer on the top of the picture is a radiator type heat exchanger; the one on the bottom is a tubular-type heat exchanger. In heat exchangers of the radiator type, the freshwater passes through the tubes and the seawater passes around them. In the tubular type, the freshwater surrounds the tubes and the seawater passes through them.