Q & A — February 2002
By Capt. Ken Kreisler
2: Outboard Cooling and more
Turn off your engine and inspect all wiring and connections. Make sure your battery terminals and ground points are tight and clean. Check the alternator belt; it should have no more than 1⁄2 inch of play midway between the two pulleys. If it still sags after tightening, or if you notice excessive wear, replace it.
Next turn on the ignition switch but do not start the engine. Check your battery-voltage meter; it should read between 12 and 13 volts. If it reads lower, something is draining it. Check for an open circuit by using your multimeter to get a reading between the alternator's positive terminal and ground. The voltage at the alternator should be the same as at the battery. If it's not, that's a strong indication that something is wrong with the alternator.
Now start your engine and check the voltage between the alternator output and ground; it should be between 13 and 14 volts. If it isn't, have your alternator checked by a qualified technician.
I'm new to outboards, and the larger boat I just bought has a tender with a two-stroke 40-hp engine. How does the cooling system work, and what kind of maintenance is required? E.M., via e-mail
The outboard's cooling system transfers engine heat directly to the virtually unlimited supply of relatively cool water in which it operates. It does this using an engine-driven water pump to pull water from an intake on the bottom of the lower unit, circulate it through all internal powerhead cavities, and pump it back out of the engine. In most outboards, this pump is located inside the intermediate unit, just above the large anti-cavitation plate.
At idle speed most of the cooling water exits through a bypass or (sometimes known as a telltale or "pee hole") on the underside of the powerhead. Water flowing from this port indicates that the cooling system is operating correctly. At anything above idle, most of the cooling water exits through the propeller since there is less backpressure here underway. The main advantage of this system is simplicity. Other than the water pump, the only other cooling system component of note is a thermostat for each cylinder bank that restricts the flow of coolant to speed warm-ups and helps maintain proper operating temperature.
The maintenance required by an outboard cooling system depends on the water it's operated in. Freshwater operation typically provides years of trouble-free service with little maintenance; saltwater less so. In either case you need to be on the lookout for exterior corrosion and the buildup of scale in internal passages that will inhibit the transfer of heat and restrict cooling water flow. Flushing the engine with fresh water after each use, or at least on a regular basis, is a good way to minimize internal corrosion. Exterior corrosion can be combated by immediately touching up any damaged paint.
In addition, the raw-water pump impeller can be damaged if run dry or when sand or grit is picked up by the pump and sucked into the system, usually when the engine is run in shallow water. A reduced flow of water from the telltale is an indication of a worn impeller. Some outboard owners tend to change their impellers every season as a preventive measure.
Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: firstname.lastname@example.org. No phone calls, please.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.