I've talked with a few sailors who recommend waiting until spring to change the oil instead of just before you put the boat away for the winter. They maintain that if new oil is allowed to sit, it leaves a deposit. Is this true?
Mark Matthews responds:
Thanks for the question. We'll assume that you're either in the Southern Hemisphere where it's now winter, or somewhere where it's so hot that your thoughts can't help but turn to the chilly season. In any event, oil should be changed at the beginning of the winter, not at the end, for a happier engine come spring. Used oil contains harmful acids that can damage sensitive bearings, valve surfaces, rings, and more if allowed to sit all winter.
In addition to changing the oil, a number of other maintenance tasks should be completed at this time. If the engine is freshwater cooled, now is the time to change the antifreeze. If the engine is raw water-cooled, now is the time to take all the salt water out of the engine as well. You should also grease the impeller and run the remaining water out of the exhaust, which will only take a few seconds of engine running time. The fuel filters can be changed if need be, belts inspected, replaced, and loosened, and the engine intake closed. (It's a good idea to write yourself a note about not starting the engine until you've re-opened the intake, and tape that note to the ignition panel).
Any cracked or chafed hoses should be replaced at this time as well as any chaffed throttle or shifting cables or suspicious electrical wiring. Now is also a good time to check pencil zincs and replace them, make sure the batteries are fully charged, and the air filter is clean. And a light coating of WD40 or similar lubricant will also help keep rust at bay on the surface of the engine.