Re: 7.5 merc how to change lower unit gear lube
Ok, in the very lowest part of the lower unit there's a big ol' flat-headed, slotted screw. This is the gearcase drain. Higher up, and sticking out the side (on the same side as the drain), is the vent screw. It's usually a more rounder-headed screw but is also slotted.
First off, if you have difficulty loosening these screws, don't strip them out or there'll be trouble!
In that case, go to Sears, your local auto parts store, or a motorcycle shop and pick up a "hand impact" tool.
This tool comes with a variety of bits and what you'll do is place it firmly on the reluctant screw and, while putting CCW pressure with your hand/wrist on the impact tool, whack the end of the tool with a hammer. This not only shocks the screw but drives it to turn, usually without stripping anything out at all.
When servicing the lower unit gear lube, have the motor in the normal (operating) position, not raised up.
Place an appropriate container underneath the lower unit and first remove the drain screw. Then remove the vent screw and more oil should come 'gushing' out.
While it's draining, take a look at the drain & vent screws. There should be a sealing washer that came out with the screw. If it's not on the screw, make sure it's still in the lower unit and in good shape. If it looks shredded or in poor shape, replace.
Once the old lube has finished draining, fill from the bottom (drain) until oil comes out of the (upper) vent in a solid stream. Reinstall the vent screw first, then remove the oil source from the drain hole and quickly reinstall the drain screw. This will minimize the spillage of oil.
A few notes:
1) Your motor uses "Hi-Vis" "Marine Grade" oil. Don't use plain old automotive 90W gear oil except in an absolute emergency. Marine Grade gear oil has the proper additives to operate in an environment where there's always the possibility you may get water into the lower unit.
2) You can pick up a quart bottle of Marine Grade gear oil at most Wal-Mart stores, a marine shop, or sometimes auto parts stores. Alongside the oil they will usually sell a little hand pump that screws into the bottle. Pick up one of those, you will really appreciate using a pump to get oil in the bottom of the lower unit, rather than trying to squeeze in a tube of oil. Much easier and way less messy! A quart will be enough for a number of oil changes.
3) Check the oil periodically during the boating season by pulling the drain plug while the motor's tilted up. Not much oil will come out but have a paper towel or shop rag ready just in case. The oil should look just about like it was when you pumped it in; if it's very dark, milky looking, or full of shiny metal filings, time to change the oil and maybe take a closer look for leaking seals or damaged innards. Change the oil before you lay up the motor for the season, and she'll be ready to go next year.
HTH & Enjoy.........ed
