Generator Pre-Trip Check: What to Inspect and Test Before a Cruise

Open the generator compartment and the sound shield. Discover Boating's Onan list starts here: ventilate the space, remove debris such as oily rags and loose parts, and clean the generator and the area around it. Fischer Panda adds a check most owners miss: press on the sound-deadening foam inside the shield. If it has soaked up liquid, find out what it is (oil, fuel, coolant or seawater) and trace the leak.

With the generator level and stopped, check the oil on the dipstick and top up only with the oil your manual specifies. Look at its color and smell; a milky look or a fuel smell needs a mechanic before you leave. If you're close to an oil change, do it now rather than mid-trip.

On a cold generator, check the level at the pressure cap as well as the recovery bottle, and top up with the right premix (see the closed cooling coolant guide). Discover Boating's Onan list says to make sure the fluids suit the temperatures you'll be running in. If you haven't tested the coolant this year, do it (see the coolant testing guide).

Look at the belt that drives the water pump and alternator for cracks, fraying, glazing or black dust, and check that it's tight as your manual describes. Southern Boating's tips put the belt on the daily check list once you're cruising. Replace a doubtful belt now and keep the old one as a spare.

Close the seacock, open the strainer, clean the basket and the bowl, and refit the lid with its seal seated. Then open the seacock again. Yachting puts this on every pre-trip check, even if you don't plan to run the generator: the water intake must be clear and the valves open.

The raw-water impeller wears and fails with age as well as hours. If you don't know when it was last changed, or it's due during the trip, change it now (see the impeller guide). Southern Boating's list says to change the seawater pump annually before the cruising season; follow your own manual for the interval. Fischer Panda also says to check the pump's seals for leaks.

Discover Boating's Onan list says to check and tighten all hose clamps and fittings, especially the exhaust connections. Squeeze the exhaust hose along its length: it should be firm, not soft, cracked or bulging. Look for soot, salt streaks or rust at joints, which point to an exhaust or water leak. Exhaust leaks are a CO risk inside the boat, so fix any you find before you go (see the hose clamp guide).

Look hard at the wet exhaust elbow too, where cooling water is injected into the exhaust. Northern Lights tells its owners to inspect it at least once a year and to replace it right away if it shows rust spots, leaks or cracks, because a failing elbow can spray seawater onto the generator's electrical parts.

Many generators have one or more zinc anodes in the heat exchanger or cooling system. Close the seacock before removing one. Replace it if it's heavily eaten away. Southern Boating suggests checking generator zincs every 90 days until you know how fast yours wear. Not every generator has them (Northern Lights, for example, says its smaller sets don't use zincs), so go by your manual's parts list rather than hunting for one that isn't there.

Look over the wiring for loose, chafed or corroded connections, and make sure the generator's mounting hardware is tight (both are on the Onan list). Fischer Panda adds pulling and reseating the control fuses and checking that relays are seated. Make sure the start battery is fully charged and its terminals are clean and tight (see the marine battery guide).

Press the test button on every CO alarm aboard and confirm it sounds. Check the end-of-life date printed on each; CO sensors wear out. Every enclosed cabin should have a marine-rated alarm (see the CO detector guide for which kind and where).

Make sure the generator's output breaker and the boat's AC load breakers are off; Southern Boating also says to turn off shore power at the dock before starting the generator. Start the generator and, as Fischer Panda suggests, watch it with the shield off for the first few minutes (keep clear of the belt and pulleys). Check:

• cooling water coming out of the exhaust within seconds
• no leaks at the raw-water pump, hoses or exhaust
• no new rattles, knocks or vibration, and a steady idle
• no warning lights or alarms on the panel, and normal volts and hertz on the meter

Then confirm you can start and stop it from every control station, another item on the Onan list. Refit the shield.

Let it warm up for a couple of minutes before adding big loads (a Cummins spokesman quoted by Southern Boating suggests about two minutes). Then switch on the loads you'll use on the trip, such as air conditioning, water heater and galley, one at a time and without overloading it (see the generator load management guide). The Onan advice relayed by Discover Boating is to run at least 80 percent of rated load for 30 minutes while watching the temperature gauge, and to check that frequency doesn't drop much below 60 Hz as load rises. Listen for the engine bogging down and look for black smoke. Yachting suggests at least 15 minutes under load with steady temperature for a generator that's been sitting more than a week. A generator that can't carry its rated load has a problem that will likely get worse on the trip; find it before you leave.

While it's under load, watch for steam in the exhaust or a temperature reading higher than usual. Northern Lights says that's the moment to check (an infrared thermometer is safer than your hand) whether the muffler and its hoses are running hot: if they are, seawater flow is restricted somewhere, usually a clogged strainer, worn impeller, slipping pump belt, plugged heat exchanger or a carbon-choked exhaust elbow. Shut down and find it before the trip.

When you're done, shut down the way Northern Lights recommends: switch the AC load breaker off first, let the generator run unloaded for about a minute to cool, then stop it. Starting and stopping under load is hard on the voltage regulator and diodes. On the trip, try to keep the generator working at roughly 40 to 50 percent of its rated load or more (typical; confirm in your manual); Northern Lights warns that long runs at very light load carbon up the exhaust elbow.

The Onan spares list for traveling boaters, published by Discover Boating, includes primary and secondary fuel filters, oil filters, an air filter, a belt, thermostat and gaskets, a seawater pump impeller and gaskets, and (for diesels) a spare injector and washer. Northern Lights, quoted by Southern Boating, gives a minimum of fuel filters, one belt, one oil filter, oil and coolant. Professional captain Vincent Daniello, quoted in the same article, suggests carrying a complete seawater pump on belt-driven units and a spare shutdown solenoid. Add the wrenches that fit and know how to bleed the fuel system after a filter change (see the fuel bleeding guide).

The Onan advice for cruising days: clear the seawater strainer before it clogs, check that nothing has moved around the generator underway (rags, tools or parts can block air inlets or chafe hoses), and check oil, coolant, belt tension, the primary fuel filter and any leaks. Write the hours in your log each day.

Record the date, hours, what you checked, the load test readings (amps, volts, hertz, temperature) and anything you replaced. Next year's readings are only useful if you have this year's to compare. Discover Boating also suggests writing down service centers along your route.