The form, location, and number of cooling passages within an engine vary considerably in dif-ferent engines. The form of a cooling water passage and its location are controlled by many factors, such as the size of the engine, the cycle of operation, and the cylinder arrangement. Many of the water passages found in various engines have been illustrated and mentioned earlier in this manual in connection with engine parts and systems. Additional information on engine cool-ing passages is given in the following paragraphs. The examples we will use are for illustrative purposes and are not all-inclusive; however, the examples described are representative of the passages that are found in in-line, V-type, and opposed-piston engines.

The location and form of the water passages in a V-type engine are basically the same as those found in an in-line engine. Differences that exist are generally due to the cylinder arrangement. The location and form of these passages at one point in a V-type engine are shown in the cross-sectional view of the 16 V 149 series engine in figure 7-12.

Figure 7-12.-Location of water passages in a 16 V 149 series engine.

Figure 7-13.-Engine coolant flow in a 16 V 149 series engine.

Figure 7-14.-Cooling-water passages in a Fairbanks-Morse 38D8 1/8 opposed-piston engine.

In operation, the water pump draws water from the off engine system and pumps it into the cylinder block through the water jacket, around the cylinder liners, and through the cylinder heads to the water outlet manifolds. (See directional arrows in fig. 7-13.) The flow of water divides in the water outlet manifolds, goes to the exhaust manifolds, and through the jacket-water outlet. The majority of the water is discharged to the jacket-water outlet. From the jacket-water outlet, the water returns to the off engine system for reuse after cooling. Water from the exhaust manifolds enters cored passages in the engine front cover and returns to the pump.

Because of differences in engine design, the location and form of the cooling passages in an opposed-piston engine will differ, to a degree, from those in other types of engines. The lack of cylinder heads eliminates some of the passages common to in-line and V-type engines. While differences of a minor nature exist in the passages of different types of engines, the cooling passages of all engines are similar in many respects. Some ways in which the passages of an opposed-piston engine are similar to those of other types of engines are shown in figure 7-14.

The liner passages of the Fairbanks Morse (FM) 38D8 1/8 shown in figure 7-14 are similar to those found in other types of engines. The loca-tion of the water header (manifold) differs in various engines. In the FM 38D8 1/8, the water from the pump usually enters the engine through the water jackets of the exhaust elbows and the exhaust manifolds. In some engines, water enters the cylinder liner through a nozzle-adapter. In the usual arrangement, the water header or manifold in the FM 38D8 1/8 receives water from the cylinder-liner water passages. In other words, the water header of an FM 38D8 1/8 is the last passage in the engine through which water flows before it goes through the cooler and back to the pump.