3. On the port and starboard sides of the engine block, remove the coolant hoses from the bottom of the exhaust manifolds.
Drain the coolant into a proper container.
Starboard shown, port similar
a - Engine block drain plug
b - Exhaust manifold coolant hose
4. Remove the hose from the heat exchanger to the water circulating pump at the pump connection. Drain the coolant into a
proper container.
5. After the coolant has drained completely, reinstall the block pipe plug and hoses. Securely tighten the clamps.
6. Remove the coolant recovery bottle from the mounting bracket and drain the coolant into a proper container.
Cleaning the Cooling System
Closed-Cooling Section
Clean the closed‑cooling section at least once every five years or whenever decreased cooling efficiency is experienced.
A good grade automotive cooling system cleaning solution may be used to remove rust, scale, or other foreign material. Always
follow the manufacturer's instructions for the cleaner.
If the closed‑cooling section is extremely dirty, a pressure flushing device may be used to flush out remaining deposits.
Flushing should be done in the opposite direction of the normal coolant flow to allow water to get behind deposits and force
them out. Refer to the instructions that accompany the flushing device for the proper hookup and flushing procedure.
Seawater Section
The cooling efficiency of an engine with closed cooling is dependent upon heat transfer through the tubes within the heat
exchanger. During engine operation, contaminants within the seawater (such as salt, silt, or lime) collect on the inside of the
tubes, reducing heat transfer and reducing the efficiency of the heat exchanger. It is recommended that the seawater section of
the heat exchanger be cleaned as specified or whenever decreased cooling efficiency is suspected. Refer to Heat Exchanger
Assembly.
Filling the Cooling System
NOTICE
Using propylene glycol antifreeze in the closed cooling system can damage the cooling system or the engine. Fill the closed
cooling system with an ethylene glycol antifreeze solution suitable to the lowest temperature to which the engine will be
exposed.
NOTICE
Air trapped in the closed cooling system can cause the engine to overheat, resulting in engine damage. Minimize the
possibility of trapping air when initially filling the closed cooling system by positioning the boat so that the front of the engine
is higher than the rear of the engine.
IMPORTANT: The closed‑cooling system should be filled with the engine cold, and should be rechecked once the engine has
warmed to normal operating temperature.
!
CAUTION
A sudden loss of pressure can cause hot coolant to boil and discharge violently resulting in serious injury from burns. Allow
the engine to cool down before removing the coolant pressure cap.
1. Remove the pressure cap from the heat exchanger.
2. Open the vent on the top of the thermostat housing to purge the air from the system.
Models with Closed Cooling
Page 6C-16 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015
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