America's Definitive Marine Engine Magazine
Before re-installing the sparkplugs, check the insulator and gap. Fouling should be removed. Even better, replace the plugs outright. Always replace spark plugs in complete sets following the manufacturer's recommendations for heat range and combustion chamber reach. On outboard motors, squeeze the rubber fuel lines, paying very close attention to the length of hose nearest the engine where heat accelerates deterioration. If a line feels mushy or bloated, or exhibits cracks, replace it. Also pump the primer bulb making sure it works freely.
Before installing starting and deep cycle batteries, top off each cell with distilled water. Tap water is not acceptable because its mineral impurities shorten battery life. Next, bring the batteries up to full charge.
Grease the battery posts and cable terminals with a thin coating of grease to help prevent corrosion. Similarly, you're about to protect the rest of the boat's electrical connections. Choose a favorite brand of moisture-displacing lubricant, then liberally spray terminal blocks, circuit breakers and wiring harness connectors. Applying spray dries out moisture and reduces the possibility of future corrosion. This is also a good time to replace blown fuses.
If the fuel tanks were topped off last fall and the gasoline stabilized, nothing needs to be done in the spring. On the other hand, partially-full tanks have likely attracted condensation. Remove any possibility of water in the gas by dosing the fuel with an appropriate additive such as Heet.
One way to determine whether there's water in the gas is to drip a small amount into the palm of your hand. If all of it evaporates it's gasoline. If little beads of water dot your hand, it's contaminated. If your fuel supply is consistently contaminated by water, installing a fuel/water separator can eliminate the hassle of dumping fuel dryer into the tanks.
Once the boat has juice, switch on the bilge pump and engine compartment blower, making certain they're operational. On outboard and sterndrive powered rigs, run the power tilt and trim up and down several times. Then check the lift pumps fluid reservoir, topping off as necessary. Turn on all the running lights and see if any of the bulbs are burned out. Honk the horn, making sure it hasn't corroded itself to death.
Last fall you removed the drain plugs from the engine block and heat exchangers and stored them in a plastic baggy along with the ignition keys. Reinstall the drain plugs.
On inboards and sterndrives, check the coolant, making sure it's topped off and the blend exhibits adequate anti-freeze protection. If the coolant is more than two years old, drain and refill. Otherwise there is a good chance the solution has lost its corrosion fighting ability.
Check the steering. (If your rig has power steering, conduct this test with the engine running) Turn the wheel hard to port, then to starboard. It should traverse freely.
Next run the throttle up and down to make sure it doesn't bind. Shifting into forward and reverse gear should lock up the prop tightly. It should not ratchet, otherwise the shift mechanism needs adjusting. In neutral, the propeller should free-wheel.
Shift and throttle cables should be replaced if they bind or have cracked outer casings. To determine correct length on replacements, measure from the control box to the stern then across the transom to the motor's connector. Add three feet to that length in order to form a loop that will prevent binding when the motor is cranked from port to starboard or vice versa.
The final step in commissioning a rig is to test run the engine so you locate problems dockside, not offshore. Once the engine's running, take it easy until it's reached operating temperature. Letting it idle for several minutes circulates fresh oil throughout and lets the seals soften. In the meantime do keep an eye out for potential problems. Check the oil filter base for leaks, and tighten as necessary. Also keep an eye out for coolant leaks, paying particular attention to the drain plugs you just reinstalled. Steam vapor is a clue you're losing coolant.
Monitor oil pressure and temperature gauges as the engine warms up. Wherever applicable check the water pump discharge that indicates raw water/coolant flow. If you're not sure whether your engine is overheating, carefully lay your hand on the cylinder head, being careful to avoid a potential burn or shock from the high tension leads. The head should be hot, but not scorch your hand. In other words, you should almost be able to lay you hand on it. However, if it's as hot as a griddle, and sizzles droplets of water, immediately shut down the engine.