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Why You Should Change Your Lower Unit Oil Every Year Changing your engine oil is a maintenance item most boat owners remember. Lower unit oil, however, is often overlooked. The lower unit, also called the gearcase, contains a set of precision gears and bearings that transfer power from the engine to the propeller. Unlike the powerhead, these components are completely dependent on clean gear lube for lubrication and protection. Replacing lower unit oil every year is one of the easiest and most af …

A lower unit problem doesn't always start with a dramatic failure. Sometimes the first clue is a new noise, difficulty shifting, unusual vibration, or something you notice while changing the gear lube. The important part is figuring out whether the problem is actually inside the Mercury lower unit, something that can be repaired individually, or damage significant enough to consider replacing the complete gearcase. If you're looking for the basics of how a lower unit works, gear ratios, fitment, …

Draining your lower unit oil is one of the simplest ways to check the health of your gearcase. If the gear lube comes out looking creamy, gray, or milky instead of its normal color, it's a sign that water has entered the lower unit. While finding milky oil isn't something to ignore, it also doesn't automatically mean you need a new lower unit. The important thing is understanding why it happened and addressing the problem before more serious damage occurs. Why Does Lower Unit Oil Turn Milky? Ge …