Boat Doc Special

When breaking in a marine engine in days gone by, I tended to take it easy—erring on the side of coddling the new motor, even more so than what was outlined by the manufacturer for the break-in period.

FFor example, if the manual said to run the engine in gear at idle for the first 15 minutes, I’d run it at idle for an hour. And if it said to run at less than half-throttle for the next two hours, I extended that to three hours.

That might have been OK with the old twostroke outboards. But with today’s four-stroke marine engines—including outboards, inboards and sterndrives—it is not a good idea.

What’s important is that owners follow the break-in schedule exactly as the manufacturer specifies; this helps ensure a lifetime of dependable performance. The owner’s manual will detail the recommended break-in procedure for your engine model.

“Failure to follow the engine break-in procedures can result in poor performance throughout the life of the engine and can cause engine damage,” states a recent blog from Mercury Marine at mercurymarine.com.

Whether your marine engine is from Honda, Indmar, Malibu, Mercury, Suzuki, Volvo Penta, Yamaha or another brand, the bearings, piston rings, cylinder walls, timing chain, valve train and other moving parts need a chance to wear in gradually in phases over approximately a 10-hour period.

On one end of the no-no spectrum is running a new engine too hard, too soon. Most new-engine owners know better, particularly given the investment in today’s marine powerplants, but running a motor too aggressively during break-in can lead to future engine failures that might not be covered by the manufacturer’s warranty.

Yet, what’s wrong with taking it extra easy on a marine motor during break-in? You have nothing to lose, right? Wrong.

If you baby the engine too much, the internal surfaces don’t get a chance to wear in sufficiently. Proper break-in requires that moving parts alternately heat up and cool down, and that means varying the

A dipstick showing an excessive oil level might be an indication of improper break-in.

engine speeds and loads during break-in. If you take it too easy and don’t vary the rpm under load, the proper heating cycles do not occur that are necessary to wear in critical surfaces.

This is especially important for the piston rings and cylinder walls. These mating surfaces need to wear in together in order to properly seal the combustion chamber. If this does not occur, the engine might suffer from blowby.

This is due to the cylinder walls and rings glazing over, which prevents them from sealing. When this occurs, it allows a minute amount of vaporized fuel to blow by the rings and into the crankcase when the motor is running, where it mixes with engine oil.

A dipstick indicating an excessive oil level and a whiff of gasoline in the oil serve as clues that this is occurring. Too much fluid can result in excessive crankcase pressure that can damage components such as the lower driveshaft seal. Plus the diluted oil can impede the lubrication of the engine’s moving parts. If you find yourself in this situation, change the oil and oil filter immediately.

Unfortunately, once an engine reaches this stage, about the only cure is an overhaul to replace the rings and hone the cylinder walls—a job best left to a qualified marine mechanic. It is an expensive lesson but one not soon forgotten, especially while breaking in that newly rebuilt motor.