Cooling System
Section 5: Cooling System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Raw Water Cooled Engines . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Cooling System Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . 127 Isolating Cooling Problem: . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Cooling System Components . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Hoses, Clamps, and Drain Plugs . . . . . . . . . . . . . . . . . . . . . . 128 Thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Manifold and Elbow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Circulating Pump - Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Supply Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Impeller Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Impeller Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Draining Engine Block or Exhaust Manifold . . . . . . . . . . . . . . . 133 3.0GS-A, 3.0GL-A/B/C/D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 3.0GS-B/C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Draining Supply Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Thermostat Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Engine Flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Sterndrive and Transom Bracket Cooling Schematic . . . . . . . 137 3.0GS/GL Engine Cooling Diagram . . . . . . . . . . . . . . . . . . . . . . 138
Description Raw Water Cooled Engines
Cooling water for the engine is picked up at the water intakes on both sides of the sterndrive lower gearcase. Water is pulled upward through the lower gearcase until it enters a water tube that transfers it to the upper gear housing. Water is pulled through the upper gear housing water passage where it meets a nipple and hose attached to the pivot housing. Water is routed through the transom mount assembly to a tube that’s mounted on the inside of the gimbal housing. From this tube the water is drawn through a supply hose that’s connected to the intake nipple of the supply pump. Water is supplied to the engine by means of an impeller type pump (raw water supply pump). The raw water supply pump is mounted on the engine crankshaft. Water supplied to the engine is circulated in the engine by means of a centrifugal type pump (circulating pump). The shape of the housing and/or liner cause an eccentric action of the impeller blades during engine operation. During periods of high speed operation, the resistance of the water on its way through the pump is sufficient to prevent the ends of the impeller blades from making con-
VPA 7743358 03-2003
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