How-To Pre-Flight A Marine Engine

5 Essential Marine Engine Checks

Modern marine engines are reliable and long living. But like anything mechanical they require someone to watch over them. Fastidious spring commissioning and fall lay-up allow marine engines to purr on for season after season. But just as important throughout the boating season is the preflight walk-through. Here are five essential engine checks designed to head off problems in order to avoid catastrophic failure.

1. Pull the crankcase dipstick. Wipe it as clean as a whistle. Then jab it back into the oil sump. This time when you draw it out of its scabbard you’ll see a true reading of the oil level. If it’s low, add just enough to bring it back to the mark. A couple of ounces low is no big deal. But if the marine engine burns a quart of oil every outing it’s critical to keep an eye on the oil level so the well doesn’t run dry and wipe out crankshaft bearings. Just as important as checking oil level is changing the oil and filter. Lubricant wears out because a hard working marine engine is like a mini refinery, busily cracking crankcase oil. High-hour engine oil gets sticky enough to gum up piston rings. Effectively frozen in their piston ring lands they stop expanding and contracting in the cylinder bore and are no longer scrape excess oil off the cylinder walls. So the oil migrates into the combustion chamber where it’s incinerated. When it does, it leaves behind carbon, abrasive carbon. That speeds engine wear.

2. Check the coolant on freshwater-cooled marine engines. That’s because overheating kills more marine engines than any other malady. Top off coolant level as necessary. Should the engine continually require replenishment it’s wise to have a professional determine exactly where the coolant is escaping. It’s also important to change coolant every couple of years. That’s because anti freeze includes an additive package that fights internal corrosion inside the cylinder block and heads. Some brands have a short shelf life, some of the newer blends boast longer. But once it’s gone stale corrosion begins to destroy the grey iron castings from the inside out.

3. Check the inboard or stern drive sea strainer for debris that could otherwise cause a clog. All stern drive and inboard engines flow raw water through sea strainers and hoses. A plugged up sea strainer is a bottle neck, or in the worst case scenario, a cork in the bottle. Without raw water to take away waste heat, the engine overheats: The cylinder heads warp the head gasket fails, engine oil temperature soars and loses lubricity, cylinder walls and pistons skirts score,  and connecting rod bearings are torn apart. Finally there's a loud bang and a big puff of smoke. The engine is dead and. You're stuck on the beach.

4. Check all of the cooling system hoses. Hoses, that flow seawater directly to the engine and to the heat exchanger can collapse under suction, obstructing water flow. A new, healthy hose feels firm and supple. An old, bad hose either feels as lifeless as a wet noodle or as hard as a rock. It should come as no big surprise to learn a hard hose is vulnerable to cracking. Besides rigidity, an early warning of a dying hose is cracking or crazing. While you are at it, also squeeze the hoses on the engine proper. Also check the hose clamps. Know that they can look good but be bad. Replace as necessary.

5. Examine the alternator and water pump drive belts. Make sure they aren’t frayed, that they aren’t checkered or cracked, signs of aging that mean the belt could let go at any moment, leaving you with an overheating engine and a draining battery. The belt should also be properly tensioned. A too-tight belt strains alternator and water pump bearings. A loose belt slips on the pulleys and can be damaged and eventually break. Also, a too-loose belt doesn’t let the alternator efficiently charge the battery or allow the water pump to circulate fluid through the engine block and heads. Deflect the belt with your thumb. There should be between 1/8 to ¼ inch play. Serpentine belts self-adjust tension.