1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 21Get this manual
MAINTENANCE
Oil Filling
IMPORTANT: Do not overfillBe sure that the outboard is upright (not tilted) when checking oilRemove the oil fill cap and refill with one US Quart (1 Liter) of oilReinstall the oil fill capIdle engine for five minutes and check for leaksStop engine and check oil level on dipstickAdd oil if necessary
Gear Case Lubrication
When adding or changing gear case lubricant, visually check for the presence of water in the lubricantIf water is present, it may have settled to the bottom and will drain out prior to the lubricant, or it may be mixed with the lubricant, giving it milky colored appearanceIf water is noticed, have the gear case checked by your dealer.Water in the lubricant may result in premature bearing failure or, in freezing temperatures, will turn to ice and damage the gear caseWhenever you remove the filldrain plug, examine the magnetic end for metal particlesA small amount of metal filings or fine metal particles indicates normal gear wearAn excessive amount of metal filings or larger particles (chips) may indicate abnormal gear wear and should be checked by an authorized dealer