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Flushing Your Outboard

A chore that can save your outboard.

Don’t forget to flush! Mom knows more about boat engines than she lets on.

The salt suspended in the water that recently floated your boat—and cooled its engine—is hazardous to your rig’s health. Long after the water has drained or evaporated, the corrosive chloride particles left behind will degrade any metal they come into contact with. The most vulnerable areas of your rig are the ports and passages inside your outboard or sterndrive engine, where the salt water was circulated by your water pump and impeller to keep the engine’s internal workings cool.

The “flushing” process directs fresh water into your engine’s cooling system to displace the salt water and wash away any potential for deposits to form.

You can flush an engine on a boat that is on a trailer or in the water at the dock; it’s important that you read your owner’s manual for recommendations. For example, some manufacturers recommend that the engine be tilted fully down for flushing.

Convenient built-in flushing port.

It’s important you flush as soon as possible, before salt water has a chance to evaporate and leave salt behind. With most engines, if you begin flushing while the engine is still warm, the thermostat will be open to allow the entire cooling system to be accessed and rinse right away; if you wait until the engine cools down you may have to operate it for several minutes in neutral before the thermostat opens.

Using a garden-style hose connected to a freshwater source, you attach the male end of the hose to a threaded flushing port built into the engine by the manufacturer or as an after-market accessory, or to a portable flushing device commonly referred to as “ear muffs.” The muffs place a flexible rubber cup over each of the engine’s water intake ports on the lower unit; one cup has a threaded fitting that attaches to the garden hose to direct the fresh water into the intake.

There are also flushing bags avail-able that you fill with fresh water, fit around the lower unit, and use while a boat is in the water—as you might want to do at the end of a day at a waterfront resort.

Exterior gets some attention.

With either type of flushing device, you simply introduce a flow of fresh water to the engine’s cooling system. With some newer outboards that offer a built-in flushing port, you should not run the engine to circulate water; gravity, water pressure from the hose, or both, do the job of getting the water to and through the cooling system. When using ear-muffs, you need to start the engine and operate it at idle speed in neutral to allow its impeller to draw and circulate the water into and through the system, replacing any salt water that remained along the way. Early in the process, you need to make sure that the water is circulating freely by checking that water is exiting the motor’s indicator jet hole or exhaust port. While doing so, note the water’s temperature; if it feels hot to the touch rather than simply warm, or is not flowing in a strong stream, it may mean that something is clogging the cooling system or that the water pump impeller is failing. If it is flowing strong and steady, check the water by wetting a finger and touching it to your tongue; allow the engine to flush for at least a minute after there is no salty taste detected in the outflow.

When you’e finished flushing, remove the engine cowling and look to see if any saltwater spray has breached it via the air intake ports. Wipe off any dampness or deposits you find, and coat the area with a light corrosion inhibitor such as CRC or WD-40. Do not coat rubber hoses or spark plug wires, as this may cause the exterior surface to expand and crack.

Rinse any metal fittings and surfaces on the outside of the boat and motor that might have been exposed to the brine. A coating of wax will offer future protection from the elements. FS

First Published Florida Sportsman Jan. 2006