Mercury Complete Outboard Lower Units
While it's easy to work on the top end of an outboard engine, sometimes you need to replace the complete outboard lower unit. You can always replace the individual components such as the propeller and gearing, but sometimes it simply isn't worth the trouble. If you replace the whole thing at once, you can rest assured that all the wear is consistent so your new Mercury lower unit will last just like the previous one.Understanding Lower Units
The lower unit is where the rotary motion changes direction from vertical to horizontal and also the location of the cooling intake. The drive shaft comes down from the engine into a gearbox, which drives the propeller shaft. The hub then holds onto the propeller. Don't forget to change the lower unit oil before every season, so that you can keep the gearbox working smoothly and check for any signs of wear.Lower Unit Cooling
The lower unit of an outboard motor contains the cooling intake for an open loop cooling system. Water comes in through the lower unit, goes up the leg and then through the engine itself. Always flush the cooling system with fresh water after running your motor in saltwater. The issue with saltwater is that if it's left inside the engine it can lead to internal corrosion, and they you could find yourself looking for a complete Mercury outboard boat engine, rather than just the lower unit.Choosing a Lower Unit
Just like with other boat accessories, there are a number of decisions you must make when you are choosing a replacement lower unit for your outboard motor. The biggest factor is whether it's compatible with your existing outboard motor. Always double check to make sure of both the model and year of the lower unit are compatible with your existing motor.Mercury Outboards
There are two main types of Mercury outboard motors, two-stroke and four-stroke. Two-strokes are very powerful, but they are extremely noisy and have a narrower powerband. Four-stroke motors are smoother and more flexible, but tend not to have as much raw power.