The location of coolers will vary, depending on the engine and the fluid cooled. Some coolers are attached; others are detached. Some fresh-water coolers are located on the outside of the hull, well below the waterline. When so located, coolers are frequently referred to as outboard, keel, or hull coolers.

Examples of variations in the locations of freshwater coolers and lubricating oil coolers can be seen in figures 7-1 through 7-4, and 7-10.

Figure 7-10.-Location of coolers and other cooling system components of General Motors Series 71 engines.

Figure 7-9.-Plate-tube cooler.

The location of the freshwater coolers and the lubricating oil coolers of the General Motors (GM) series 71 engines (fig. 7-10) is representative of the location of the coolers in many small diesel engines. In this system of engine cooling, the hot coolant leaving the thermostat housing passes through the expansion tank, then through the cells of the cooling core. After leaving the heat exchanger, the engine coolant is picked up by the freshwater pump and circulated through the cylinder block and cylinder heads.

The raw water (seawater) is forced horizontally between the cells of the core and serves to lower the temperature of the coolant as it passes through the cells. The location of the coolers in a medium-sized diesel differs from that in smaller engines.

The coolers discussed up to this point have been those that function to lower the temperature of fresh water and lubricating oil. In some engines, the temperature of the supercharged intake air is also reduced. If the temperature of this air, which is heated by compression within the supercharger, is reduced, then the amount of air charge entering the cylinder during each intake event will increase and the power output of the engine will be increased. Coolers that function to lower the temperature of the intake air are primarily of the radiator type and operate on the same principle as coolers that function to cool fresh water and lubricating oil. Air coolers that serve to cool intake air are referred to as intercoolers or after-coolers. The heated air from the supercharger passes around the tubes, where the heat is transferred to the cooling water that is flowing through the tubes. The cooling water is generally from the seawater circuit, but it may be from the freshwater circuit.

The engine cooling system also functions to cool the air around some engine-generator sets. Generators, unlike internal-combustion engines, cannot be directly cooled by liquids. If a generator develops more heat than can be removed by the surrounding air, a supply of cool air must be provided in a closed air circuit. The heated air from the generator is forced through the cooler, where the temperature is reduced. The air is then recirculated to the generator. Depending on the installation, either fresh water from the engine cooling system or seawater may serve as the cooling medium.