Changing Your Lower Unit Lubricant
Submitted by Mark ("MOFish") Hofman
Regular maintenance on your outboard is critical to its longevity and performance. But admittedly, most outboards today are as sophisticated as the engine under your car or truck's hood. Computers, sensors, wiring and some unique components (Stator?...What the %$*@ is a stator?) can pose some challenges to the shade tree or house garage mechanic.
Before I go on, understand one thing. I'm a white-collar, paper-pencil pushing GEEK who just happens to enjoy fishing. And I most enjoy fishing out of a boat. I also love squeezing every nickel 'til the buffalo poops (hey...I'm not uncivilized). In other words, I look for ways to save money and I've learned one way to save some money that I can share with you here.
There is one annual maintenance item that even guys like ME can perform: changing the lower unit lubricant (oil) on my outboard motor.
The Project Boat
2001 Tracker Tournament V-18SE
2002 Mercury 150XR6
Tools and Supplies
As you can see from the photo to the left, you'll need a few things to get the job done.
New Lower Unit Lubricant (bottle or tubes)
Oil Drain pan
Replacement fiber washers
* Optional, but necessary if
you're using lubricant from a new bottle.
The Procedure HINT: Give yourself some room to work. You'll be down on your knees for a lot of this.
The first step is to place the drain pan under the lower unit. Tilt the outboard as vertical as it can go. My outboard won't go all the way vertical, so I positioned it in such a way that the drain hole would be as low as possible. My skeg ended up resting on the edge of the drain pan, so I had to stop there.
With the drain pan in place, unscrew
the drain/fill (lower) plug. I call this the drain/fill plug
because it is the plug for the hole through which you'll drain the old lubricant and use
to fill the lower unit with new lubricant. Mine needed a flat-head
screwdriver. It takes a good seven or eight turns to get the plug out.
As long as you take the bottom (drain/fill) plug out first, you shouldn't have lubricant all over your hands. The top (vent) plug should still be in place. If it is, the vacuum formed will keep the lubricant from draining out around the plug before you can get it out. A small bit will leak, but that can't be avoided.
Before you set the drain/fill plug aside, take a look at it. Do you see any metal chips or shavings stuck to it? Some plugs have a magnet which will attract larger pieces of metal. If you see anything bigger than a speck, you should probably have a mechanic check your lower unit for excessive wear.
Nothing? Okay, now look to see if a fiber washer came out attached to the plug. If it didn't, you'll need to fish that washer out of the drain hole because we're going to be replacing it.
Set the plug and old washer aside, onto a paper towel or rag that can absorb the oil.
Now, remove the vent plug from the top hole. As you get it loose, the gear lube will begin to drain at a steady pace out of the drain hole into your collection container. Some outboards will have two vent screws. (Why? I have no idea. Maybe to help the old lubricant drain out easier. If that's the case, remove both vent plugs.) You may need to leave them out when you go to fill the unit as well. Ask a mechanic who knows your brand of outboard.
Be sure to also inspect that top plug for metal
shavings - and the make sure you've removed the old washer as well. Set
both off to the side with the first plug. In the photo at left, you see
the two plugs, one of the old washers (the other is still attached to a plug)
and the two new washers I'll be using to replace the old ones..
Here's a word of warning: lower unit lubricant is like molasses. It is thick, and it is sticky. One thing to watch for as the lubricant drains is it's color. If you see any milky-colored water or oil drain out, that means you probably have a bad seal and water is getting into the lower unit. Just like metal shavings or chips on the plug screws, this is a sign that a qualified mechanic should inspect the lower unit and make any needed repairs.
You may also see some "glitter" in the oil. As long as it has the appearance of dust or very fine particles, you're okay. This is just a sign of normal gear wear. Below is a picture I took showing the dust. I ran my finger through the lubricant to see if I could feel any chips or slivers of metal. When you click on the picture, another window will open with a magnified view. You should be able to spot the "glitter"
It's going to take longer to completely drain your lower unit than it does for 10-W30 to drain out of your car. So go take a break. Watch some football. Rake the leaves, or run some errands. We'll go on with the next part after the oil has completely drained out of your lower unit.
<< Cheesy bossa nova music plays in the background. In the meantime, the instructor has gone to the bathroom. Either that, or his wife has told him to get off the computer so she can check her e-mail. >>
Okay. First, clean up any oil that is still stuck to your bullet and skeg - as much as possible anyway. You may still get a dribble of lubricant as we go along, but it makes for a clean work area.
Lower unit lubricant comes in either bottles or tubes. I needed 24 ounces to fill my lower unit, so I bought one 32-ounce bottle rather than a two or three of the 10-ounce tubes. (Okay, so I don't really know how much comes in a tube; I bought the bottle because I could use the pump accessory which was pretty cool. )
A VERY IMPORTANT WORD OF CAUTION: A couple of folks also were kind enough to point out to me that you shouldn't mix two different types of lubricant. For example, if you're working on a Mercury outboard and you use Mercury Quicksilver Premium Plus lubricant, stick with that. If your outboard come with Quicksilver Premium, use that. This is most likely to occur if you use the tubes, since one tube alone won't fill the lower unit. If you can't get two tubes of the same type, don't "cheat" and buy a tube of a different type!! I made sure my lower unit was completely empty and then filled from ONE 32-ounce bottle; so I couldn't mix two different types.
Before we start filling the lower unit, put the new, replacement fiber washers onto both the vent and the drain plug screws, and set the screws close by where you can reach them easily.
Assemble the pump and attach it to the bottle - or cut the tip off of the tube if you're using tubes. Then attach the tube or the end of the fill hose to the drain/fill hole - not the top hole!
I can't stress this enough. Do not attempt to fill the lower unit from the top hole, and do not put the vent plug back into the top hole until I tell you to!
You're going to fill the lower unit from bottom to top. Why? You don't want new lower unit lube running out of the bottom hole (because you haven't put the drain plug back in, right?) and you don't want to fill the lower unit with the vent plug in because you'll trap air at the top of the unit - and trapped air is a very BAD thing!
The picture at left shows how the hose is hooked up to the bottom drain/fill hole. If you're using tubes, stick the neck of the tube up into the hole and begin squeezing lower unit lubricant into the outboard. If you're using a pump, like me, pump the lubricant in slowly. You'll get some air bubbles into the lower unit, but we'll deal with that later.
Keep pumping until you see new lubricant coming out of the vent (top) hole. If you're using tubes and need to switch to a second or third tube, have a friend hold their finger over the vent hole to keep the lubricant from draining back out.
Is lubricant coming out of the vent hole? Okay NOW you can re-install a plug and washer into the vent hole. Be sure to tighten it down with the screwdriver. But, for the moment, leave the pump/bottle or tube connected to the drain hole.
There is one final step, and how you do it depends on the what kind of container you're using - bottle/pump or the tubes.
Here's a trick that only works with the bottle and pump: Take another break and let any air bubbles work themselves up to the top of the lower unit chamber. They move about as fast as air bubbles through clear shampoo. When a sufficient amount of time has passed, put a couple of pumps of lubricant into the lower unit with the top plug still in place. This pressurizes the oil in the unit and compresses the trapped air. Now, take your screwdriver and slowly loosen the screw. If any trapped air exists, you'll hear a *puff* of air come out around the edge of the vent screw. Re-tighten the screw and repeat the process. When all the trapped air has been forced out, lower unit lubricant will come squirting out around the edge of the screw. Tighten that screw back up. Then remove the hose and adapter from the drain/fill hole and reinstall the that plug and its washer. Make sure both the lower and the upper screws are in good and tight. You don't want water leaking in past these screws.
If you're using tubes: as soon as the lubricant comes out of the vent hole, re-install the top plug, and then remove the tube. Reinstall the lower plug and wait overnight. The oil will settle to the bottom and the air will move to the top. In the morning re-attach the tube, remove the top vent plug and squeeze some more lubricant in until it comes out of the vent hole. That's probably the best you'll be able to do to get the air out. Reinstall the drain/fill plug and its washer. Make sure both the lower and the upper screws are tight.
Finally, wipe off any excess gear lubricant from the lower unit casing. Clean your pump (if you've use one) using hot water and a good amount of Dawn dishwashing detergent. Keep the pump disassembled so that it dries completely.
That's it! You've just completed a necessary - and fairly easy - annual maintenance item! Questions or comments about this article? Email me! And feel free to point others to this article as well.