Boat motor cooling systems work by drawing water into the lower unit of the motor using its impeller pump. Water is circulated through a system of ports and passages and then out the water exhaust port carrying with it excess heat. Boat motors can be damaged if salt and silt are not flushed from the cooling system. Flushing a boat motor can be accomplished hooking a garden hose to a flushing device which directs fresh water into the motor's cooling system intake. The motor's impeller pump circulates the fresh water through the cooling system and out the water exhaust port along with harmful salt and silt. The most common flushing device, known as 'ear muffs', consists of two rubber cuffs connected by a U-shaped soft steel bracket which can be bent for a better fit. One of the cuffs has a fitting to which an ordinary garden hose can be attached. Some newer motors have a flushing attachment built in. Refer to your owner's manual for instructions.
Attach the flushing device so the cuff with the garden hose is over the cooling system intake port on the lower unit.
Shift the motor into neutral.
Turn on the water about half way. Too much pressure may unseat the flushing device cuffs.
Start the motor and set the throttle to idle.
Check to see that a steady stream of warm water runs from the outlet port. Hot water, water dribbling out, or no water can mean the outlet tube is clogged or the impeller pump is failing. Turn off the motor immediately and unplug the opening or replace the impeller pump.
Sample the cooling water for salt by tasting. Insure thorough flushing by running the water for a minute after the flush water is no longer salty or is clean and free of silt.
- Be certain the motor shift lever is set to neutral before starting the motor.
- Shut off the motor immediately if you suspect water is not circulating through the cooling system and the motor is running hot.
- Check the owner's manual for directions specific to your motor. Some manufacturers recommend the motor be tilted for thorough flushing. For added safety the propeller can be removed.