all of the drain cocks open until refilling the cooling system.
The exhaust manifolds of marine engines are cooled by the same coolant used in the engine. Whenever the engine
cooling system is drained, each exhaust manifold drain cock, located on the bottom near the exhaust outlet, must be
opened. Raw water pumps are drained by loosening the cover attaching screws. It may be necessary to tap the raw
water pump cover gently to loosen it. After the water has been removed, tighten the screws.
The cooling system should be flushed each spring and fall. The flushing operation cleans the system of antifreeze
solution in the spring and removes the summer rust inhibitor in the fall, preparing the cooling system for a new solution.
The flushing operation should be performed as follows:
1. Drain the previous season's solution from the engine.
2. Refill the cooling system with soft clean water. If the engine is hot, fill slowly to prevent rapid cooling and distortion of
the engine castings.
3. Start the engine and operate it for 15 minutes to circulate the water thoroughly.
4. Drain the cooling system completely.
5. Refill the system with the solution required for the coming season.
Cooling System Cleaners
If the engine overheats and the fan belt tension and water level are satisfactory, clean and flush the entire cooling
system. Remove scale formation by using a quality de-scaling solvent. Immediately after using the solvent, neutralize
the system with the neutralizer. It is important that the directions printed on the container of the de-scaling solvent be
thoroughly read and followed.
After the solvent and neutralizer have been used, completely drain the engine and radiator and reverse-flush before
filling the cooling system.
After the engine and radiator have been thoroughly cleaned, they should be reverse-flushed. The water pump should be
removed and the radiator and engine reverse-flushed separately to prevent dirt and scale deposits clogging the radiator
tubes or being forced through the pump. Reverse-flushing is accomplished by hot water, under air pressure, being forced
through the cooling system in a direction opposite to the normal flow of coolant, loosening and forcing scale deposits out.
The radiator is reverse-flushed as follows:
1. Remove the radiator inlet and outlet hoses and replace the radiator cap.
2. Attach a hose at the top of the radiator to lead water away from the engine.
3. Attach a hose to the bottom of the radiator and insert a flushing gun in the hose.
4. Connect the water hose of the gun to the water outlet and the air hose to the compressed air outlet.
5. Turn on the water and, when the radiator is full, turn on the air in short blasts, allowing the radiator to fill between air
CAUTION: Apply air gradually. Do not exert more than 30 psi (207 kPa) air pressure. Too
great a pressure may rupture a radiator tube.
6. Continue flushing until only clean water is expelled from the radiator.
The cylinder block and cylinder head water passages re reverse-flushed as follows:
1. Remove the thermostat and the water pump.
2. Attach a hose to the water inlet of the cylinder block to drain the water away from the engine.
3. Attach a hose to the water outlet at the top of the cylinder block and insert the flushing gun in the hose.
4. Turn on the water and, when the water jackets are filled, turn on the air in short blasts, allowing the engine to fill with
water between air blasts.
5. Continue flushing until the water from the engine runs clean.
If scale deposits in the radiator cannot be removed by chemical cleaners or reverse-flushing as outlined above, it may be
necessary to remove the upper tank and rod out the individual radiator tubes with flat steel rods. Circulate water through
the radiator core from the bottom to the top during this operation.