How to Change Your Gearcase Lube

Your lower unit gear lube is often the victim of out-of-sight-out-of-mind disregard.

It’s under the water whenever you’re using your boat, of course, and even when the boat is on the trailer it’s easy to walk right past it without a second thought. It’s sealed up, and there’s no dipstick to check it, so if you don’t see oil dripping in your driveway, it’s not something you need to be concerned about, right? Wrong. Your outboard gearcase is a vital link between your powerhead and the water, and its gear lube gets absolutely punished as it protects your gears, shafts and bearings from heat and friction. Neglecting your lower unit gear lube is simply a chance you don’t want to take.

Hopefully you’re already following your owner’s manual’s recommendation for checking your gear lube level at regular intervals. But every season or every 100 hours – whichever is sooner – you’ll still need to drain the lower unit and refill it with new gear lube, using a premium product that is formulated for your model of engine, such as Quicksilver® Marine Lubricants Premium Gear Lube.

Some boaters elect to have a dealership change their gear lube during an annual service visit, but it can also easily be done by just about anyone with a few basic tools. In fact, it’s a perfect chore for someone who wants to get more hands-on with their boat maintenance but is not quite ready to tackle more complicated service items.

Whether it’s your first lower unit gear lube change or your hundredth, the procedure is fast and easy. In this Quicksilver Blog video, we’ll demonstrate on a 115hp Yamaha four-stroke, but the procedure is almost identical for many other outboard brands and models.

1. Gather your supplies. You’ll need:
   1. A flathead screwdriver
   2. Quicksilver Gear Lube Pump Kit
   3. Oil catch pan
   4. 1 quart of Quicksilver Premium Gear Lube; for other brands and models, check your owner’s manual to see how much gear lube will be needed
   5. Paper towels or a couple of rags
   6. Nitrile gloves
      Note: The Quicksilver Gear Lube Pump Kit is reusable, so you’ll only need to buy it once.
2. Trim the outboard to the vertical position. Vertical doesn’t mean it should be tucked all the way under; it means that the crankshaft of the powerhead should be as close to vertical as possible and the propshaft should be parallel to the ground. You’ll also want to adjust the steering wheel or tiller to get engine in the straight-ahead position.
3. Turn off the main battery switch to negate the chance of an accidental start.
4. Position your catch pan under the gearcase drain plug, which is typically on the right side of the lower unit at the junction between the torpedo and the skeg. A piece of cardboard placed under the pan will help catch any stray drips or small spills.
5. Using your screwdriver, remove the drain plug and inspect it to ensure that its gasket is in good shape. If the gasket is damaged, you’ll need to get a new one from a marine retailer before you proceed.
   1. Important: The drain plug is magnetic, so check it for metal shavings. A fleck or two of metal is normal, but if you see more than a tiny bit of metal clinging to the plug, STOP THERE and get your lower unit inspected by a qualified marine technician. It might be nothing, but it might be a sign of an impending failure.
6. The lube will start to drip out, but to get the gearcase to drain properly you’ll need to remove the upper oil level/vent screw. It looks similar to the drain screw and is located near the top of the gearcase. Inspect its gasket for damage as well.
7. The oil should start draining quickly, so make sure your pan is properly positioned. Most of it will be evacuated in a couple of minutes, but let it drain until the flow subsides to a slow drip (usually 10-15 minutes) before proceeding.
8. Check the drained oil for metal and signs of contamination. If the spent lube is milky, it likely means you’ve got a failing seal and need to have it looked at by a professional.
9. If the used gear lube looks good, you’re ready to refill the gearcase. Assemble your pump kit, then insert the pump into the new bottle of gear lube and tighten the cap. Then screw the end of the pump hose fitting to the drain hole by hand until snug. (Do not use upper vent hole for filling. Outboard lower units are designed to be filled from the bottom.)
   1. Tip: The pump kit comes with an adapter fitting so it will fit a wide variety of outboard brands, so make sure you use the adapter if that’s what fits your engine. Also, it’s sometimes easier to attach the hose to the gearcase before putting the pump in the bottle. This is fine, but make sure you don’t get any dirt or debris on the pump in the process.
10. Pump in the new gear lube. Keep pumping until oil starts to come out of the upper vent hole. A 115hp Yamaha four-stroke gearcase takes just under a quart of lube, but this will vary by engine model and brand.
11. Make sure the upper oil level/vent screw is clean, dab a bit of new gear lube on the threads, then replace it and tighten it down. This must be done before removing the hose from the drain hole to keep the new gear lube from draining out while replacing the drain plug.
12. Clean and pre-lube the treads of the drain plug and set it close by. Unscrew the pump hose and quickly put the drain plug back in place, taking care that you don’t cross thread it. A few drops of gear lube might escape before you can get the plug in, but this is normal. Tighten the drain plug firmly with your screwdriver, then double check it and the upper screw as well.
13. Clean up your lower unit with paper towels or a rag, then properly dispose of them and the used gear lube.

For more tips and instructional videos, checkout the Marine section of the Quicksilver Blog.