Best Oils For Boat Lower Units: A Comprehensive Guide

Choosing the right oil for your boat's lower unit is essential for keeping your vessel in good shape. While you can always consult a boat mechanic, changing the oil yourself is a simple process that only requires a few tools and the right type of oil. It is important to note that the oil should match the engine manufacturer's recommendation to ensure the best fit and avoid potential complications. For marine use, any brand of oil with a grade designation of API GL5 SAE 80 or 90 weight is suitable. Additionally, it is crucial to change your lower unit oil regularly, at least once a year, to prevent damage to the gears from heavy loads.

What type of oil is needed for a boat lower unit?

The type of oil you need for your boat's lower unit depends on the manufacturer's recommendation and the power of your outboard motor.

Manufacturer Recommendations

Firstly, it is important to check the engine manufacturer's recommendation for the type of oil to use in your boat's lower unit. This is the best way to ensure the best fit without potential future complications.

Outboard Motor Power

The power of your outboard motor will also determine the type of oil you need. For outboards below 75 horsepower, SAE 80W90 Gear Lube is recommended. For higher-powered outboards, an oil with a grade designation of API GL5 SAE 80 or 90 weight is suitable.

Marine-Grade Oil

It is essential to use oil that is suitable for marine use. Using a lubricant meant for an automobile could potentially damage your engine or void your warranty. Marine-grade oils have special anti-foaming agents that are not present in regular automotive gear oil.

Popular Brands

There are several popular brands of lower unit oil available, including Mercury, Quicksilver, Johnson, and Yamaha. Prices for these brands range from around $15 to $30.

How much oil is needed for a boat lower unit?

The amount of oil needed for a boat lower unit varies depending on the model of the boat. For instance, the amount of oil required for a Tohatsu outboard motor differs based on the model. The amount of oil needed ranges from approximately 2.5 fluid ounces for the 2.5 & 3.5 (4-stroke) model to 250 fluid ounces for the BFT200 & BFT225 & BFT250 (4-str.) model.

It is crucial to refer to the owner's manual to determine the precise amount of oil required for your specific boat model. The owner's manual will also specify the grade of oil recommended for the lower unit, such as 90W or 80W-90.

When changing the oil in your boat's lower unit, it is essential to follow the manufacturer's instructions and safety guidelines. This typically involves draining the old oil, ensuring the oil is completely drained, and refilling the unit with the appropriate type and amount of oil.

It is worth noting that the frequency of oil changes depends on how often you use your boat. As a general guideline, it is recommended to change the oil at least once a year, but if you use your boat more frequently, you may need to change the oil every 100 hours of operation or every six months, whichever comes first.

Additionally, it is important to use oil that is specifically designed for marine use and to avoid mixing different brands or types of oil.

How often should the oil be changed?

Regular maintenance is essential if you want your boat to last. One task that should not be ignored is changing the oil in your boat's lower unit. The oil in your boat's lower unit should be changed at least once a year, though this will vary depending on how often the boat is used.

Oil Change Frequency

Changing your boat's lower unit oil is a form of preventative maintenance that will keep your boat in good condition. At a minimum, the oil should be changed once a year. However, this is based on the assumption that the boat is only used occasionally. If the boat is used more frequently, the oil will need to be changed more often. As a rule of thumb, the oil should be changed every 100 hours of operation. This is similar to how cars should receive an oil change every 30,000 miles.

Benefits of Regular Oil Changes

Regular oil changes are important because they help to keep the engine clean and prevent damage. Used oil contains contaminants and moisture that can corrode the engine, especially if the boat is stored away for long periods. Fresh oil extends the life and service of boat engines, improves engine performance, and prolongs the engine's lifespan.

When to Change the Oil

In addition to regular oil changes, it is recommended to change the oil before storing the boat for the winter. Research suggests that a boat's engine lasts 50% longer when stored with clean oil. If the boat is used frequently or for towing, the oil may need to be changed twice in one season. For new engines, the oil should be changed after the first 20 hours of use, then every 100 hours or yearly.

What is the process for changing the oil?

Servicing the lower unit of your boat's engine is a simple job that can be done at home. It is important to change the oil regularly to protect the gears from damage and to prevent the need for costly repairs. The process is relatively straightforward and can be completed in a few easy steps.

Firstly, ensure your outboard is in a vertical and upright position. Locate the upper and lower Fill & Drain Plugs. Place an oil drain pan beneath the outboard to catch the oil. Remove the bottom drain plug first, followed by the top drain plug. This will release the vacuum and allow the oil to drain freely.

Let the oil drain completely. This may take up to an hour. Once drained, it is time to refill the lower unit. You can use any brand of lubricant with a grade designation of API GL5 SAE 80 or 90 weight, ensuring you do not mix different oil brands or weights. Insert the bottle/tube into the bottom drain hole and slowly squeeze the bottle to force the oil into the lower unit. Continue adding oil until it flows freely from the top hole without air bubbles.

Keep the bottle/tube in the bottom plug and reinstall the top plug to create a vacuum and minimise oil loss. Then, quickly remove the bottle/tube and reinstall the bottom drain plug. Tighten both drain plugs and wipe away any excess oil.

Finally, dispose of the old oil at an oil recycling centre.

What are some good oil brand options?

When choosing an oil brand for your boat's lower unit, it's important to select one that's suitable for marine use. Using a lubricant meant for automobiles can potentially damage your engine or void its warranty. The oil should also have a grade designation of API GL5 SAE 80 or 90 weight. Here are some good oil brand options that meet these criteria:

• Quicksilver by Mercury Marine offers both 80W-90 Premium Gear Lube and 90 High-Performance Gear Lube.
• Mercury Marine also provides High-Performance Gear Lube with a Hand Pump.
• Yamaha offers a Lower Unit Gearcase Lube Quart, as well as Marine Gear Lube HD.
• Lucas Oil provides Synthetic SAW 75W-90 M8 Marine Gear Oil.
• Valvoline offers High-Performance SAE 80W-90 Gear Oil and FlexFill Full Synthetic SAE 75W-90 Gear Oil.
• Mobil 1 offers 75W-90 Synthetic Gear Lube.
• LubriMatic offers High Viscosity Lower Unit Gear Lube.
• Sierra offers Synthetic Gear Lube Oil.
• TRIAX offers Marine Gear Oil SAE 90, which is full synthetic and compatible with all stern drives, bow thrusters, and lower gear units in boats and jet skis.

The prices for these brands on Amazon range from around $12 to $30. It's worth noting that prices may vary depending on the retailer and that you should always follow the engine manufacturer's recommendations for oil type to ensure the best fit for your boat's lower unit.

Frequently asked questions