Lower Unit Gear Lube Change in a Mercury Outboard
Maintaining your Mercury outboard lower unit provides a peace of mind knowing that your boat’s motor will function efficiently when out for a day on the water. Mercury lower unit lube changes are an important part of maintaining an outboard motor. Changing the lower unit oil (gear lube) of a Mercury outboard provides the proper lubrication for the internal components of the motor, while removing normal shavings from the oil. Also having a look at the oil during a Mercury outboard lower unit oil change will give you details on the state of the motor’s internal components.
Read on for instructions on performing a gear lube change or watch the video for you motor…
1. Prepare to Drain: First, you need to ensure that your outboard is in a vertical and upright position. Then you will need to locate and identify both the upper and lower Fill and Drain Plugs. Place an oil drainage pan beneath the outboard where you will remove the bottom drain plug. Some oil will begin to trickle out so you need to make sure that the oil drain pan is positioned correctly to catch the draining oil.
2. Drain the Gear Lube Oil: Now remove the top drain plug; this will release the vacuum that exists and allow the oil to drain freely from the Mercury lower unit. Allow all of the oil to drain completely from the lower unit. This process can easily take between 5-10 minutes.
Once all the oil has been completely drained, the lower unit will have to be re-filled. There are various tools available in order to re-fill the oil, such as squeeze bottles and tubes. It seems that the easiest way for most people is to use the Mercury pump & fill tube.
3. Add Gear Lube Oil: To refill the lower unit, insert the bottle or tube into the bottom drain hole and slowly squeeze the bottle or push the pump down to force the oil into the lower unit. We recommend original manufacturer marine oil for best performance and longivity. Read more about brand name vs generic oils here.
Continue to add oil until the lubricant is flowing freely from the top hole and is free from any air bubbles. Keep the bottle or tube in the bottom pug and reinstall the top plug. Quickly remove the bottle from the bottom hole and install the drain plug. It is important to do this as quickly as you can to minimize the total amount of oil loss. Even though there is a slight vacuum there will be some loss of oil.
Tighten both the lower and upper drain plugs and wipe off any oil that may have fallen on to your lower unit.
A marine specific lower unit gear lubricant should only be utilized in a Mercury outboard. The additive in such oil is normally of a higher water demulsability and has corrosion protection. Failure to use your manufacturer’s gear lube and oil can have devastating, costly results.
Always ensure your lower unit oil has the following properties in order to function correctly:
- Excellent seal compatibility
- Excellent resistance to water and moisture
- Great protection of components from rust and corrosion in dry conditions and in moist conditions
- Enhanced gear, bearing and seal cleanliness
Also, be sure to consult your outboard motor’s owner manual to verify the steps above are in agreement with the manufacturer’s recommendation for changing lower unit oil.
Gear Lube Change 20-40 Hp
Gear Lube Change 40- 300 HP
Lower Unit Oil Change for 15- 20 HP
FourStroke: I-2 333cc 15hp and 20hp
ProKicker: I-2 333cc 15hp
Lower Unit Oil Change 40 - 300 HP
Verado: V-8 4.6L 250hp AMS and 300hp AMS
FourStroke: I-3 747cc 40hp; I-4 995cc 40hp CT, 50hp, 50hp CT, 60hp, 60hp CT; I-4 2.1L 75hp, 90hp, 90hp CT, 115hp and 115hp CT; I-4 3.0L 150hp; V-8 4.6L 250hp and 300hp; V-6 3.4L 175hp, 200hp and 225hp
Pro XS: I-4 2.1L 115hp and 115hp CT; I-4 3.0L 150hp; V-8 4.6L 200hp, 225hp, 250hp and 300hp; V-6 3.4L 175hp