To keep your boat in good condition and out on the water, you occasionally need to change the oil. Most manufacturers recommend a gearcase lower unit oil change annually or after 100 hours for frequent boaters who reach that number first. You can do this yourself in minutes by following our step-by-step outboard motor oil change guide.

The Importance of Regular Maintenance for Marine Engines

Changing your gearcase oil is crucial for boat performance. It keeps internal components lubricated, preventing parts like gears, bearings and other gearcase components from wearing out and failing. Proper boat gearcase maintenance, including oil changes, can help prevent costly damages and keep your boat running to its destination and back.

With reliable outboard motor components and regular maintenance, your boat can last for many adventures on the water.

Preparing for Your Gearcase Oil Change

Your DIY oil change will go more smoothly if you're prepared. Be sure you have the right type and amount of oil and all the necessary tools.

Choosing the Right Oil

Before you begin your gearcase oil change, you'll need to find the right oil for your boat. A quality lubricant protects components from metal-on-metal, heat and water damage.

Remember that being on the water and the road are very different situations. While there is some overlap between the functions of marine and automotive gear oil, there are significant differences. You should always use genuine marine gear oil rather than automotive oil for your outboard motor.

Choose a four-stroke outboard engine oil with NMMA® FC-W® approval. This guarantees a standard of viscosity, wear prevention and corrosion protection that can handle your outboard engine's revs and the stresses of the marine environment around it.

Check the manual provided by your boat's manufacturer for further specifications on the type and weight of oil you should be using.

How Much Lower Unit Gear Oil Do I Need?

When refilling the gearcase in your lower unit, using the right amount of oil is essential. This will protect your outboard components and keep your boat running safely.

The right amount of oil depends on the capacity of your specific outboard motor model. The manufacturer should specify this in the manual. You'll know you've filled the lower unit with enough gear oil when the new oil begins flowing out of the top drain plug hole.

Tools and Equipment Needed

In addition to your lubricant, you'll need some basic equipment and tools to complete a successful oil change. Make sure you have:

• Drain bolt gaskets
• A screwdriver
• An oil collection pan
• A dipstick
• A clean rag
• A gearcase oil change pump or squeeze bottle

An oil change pump is the most efficient tool to speed up your oil change, but a squeeze bottle can get the DIY job done if you're not ready to invest in a pump yet.

Some boat manufacturers offer oil change kits as a convenient solution. These kits generally include certified engine oil, a filter and the appropriate gaskets or seals for your boat.

If you have all these parts and tools plus quality marine gear oil, you can start changing your gearcase oil.

The Step-By-Step Guide to Changing Your Gearcase Oil

The following steps will guide you through the process of doing your own gearcase lower unit oil change in two main phases — draining the old oil and refilling the gearcase with new oil.

Draining the Old Oil

Follow these 10 steps to drain the old oil from the lower unit:

1. Position the boat on a flat surface, ensuring the outboard engine is vertical and upright.
2. Warm the engine to operating temperature, as warming oil helps speed drainage along.
3. Find the bottom and top drain plugs.
4. Place an oil collection pan under the bottom drain plug.
5. Using a screwdriver, unscrew the drain and vent screws to remove the bottom plug.
6. Oil will drain slowly. Ensure your container is in place to catch it.
7. Remove the top drain plug.
8. Oil will now drain more quickly from the lower unit.
9. Wait five to 10 minutes for the oil to drain.
10. Check that the oil has drained completely from the lower unit.

Once you've removed the old oil from the lower unit, you can refill your gearcase with new oil.

Refilling the Gearcase With New Oil

Once you've drained the old oil from the lower unit, it's time to refill the gearcase. You can do so by following 10 more simple steps:

1. Insert the bottle or tube into the bottom drain hole. 
2. Slowly squeeze or pump to fill the lower unit with lubricant.
3. Continue until the oil is flowing from the top hole without air bubbles.
4. Keep the bottom hole plugged with the bottle or tube, and re-install the top plug. 
5. Remove the bottle or tube from the bottom hole and insert the drain plug quickly. 
6. Some oil loss will occur. A small amount isn't concerning.
7. If excessive oil loss has occurred, add additional oil. Check the oil level with a dipstick to decide if this is necessary. 
8. Wipe off spilled oil from your lower unit.
9. Tighten both drain plugs and any screws you removed during the oil change.
10. Discard old oil at a recycling center or supply store with a collection point.

After following all the steps to drain and refill your outboard, you'll have successfully completed your DIY outboard motor oil change.

How Fawcett Boat Supplies Can Help

Fawcett Boat Supplies is your one-stop supplier for completing an outboard motor oil change and any other DIY boat maintenance tasks.

Our online store and physical outlet in Annapolis, Maryland, carry a broad inventory of boat supplies from top brands like Honda, Suzuki, Yamaha and Tohatsu. Our experienced staff also service outboard motors by many manufacturers.

If you have any questions about the best products or services for your boat, contact our helpful sales team.