Use your large slotted screw driver and remove the lower plug see image below. If you see residue in the bottom of the bottle it should be removed and rinsed out with carb cleaner or Power Tune. Water will rust the bearings, races, gears and shafts and it will ruin the drive in just a short time. Re-tighten both screws with your large slotted screwdriver. Please take a moment to donate now.
Use a sharp pointy pick and make sure to remove the old drain plug gaskets from the drain and vent holes. Every boat owner should check the level and the condition of his lower unit gear case oil, as often as prescribed in the manufacturer's's service manual. No oil on your finger, or oil that sits below the vent hole opening, means you need to add lower gear case oil. Pressure in the system will make a mess when the hand pump fitting is removed from the bottom fill hole. My Alpha One Gen 1 doesn't have a reservoir wish it did though. This is made easy with the use of a Gear Lube Pump.
If you have found water in the lube, or if you suspect the drives seals are leaking, you should pressure test the drive while it is empty. Mercruiser owners should be aware of the recommended fuel for their engine. Mercury recommends that you change your sterndrive oil every year or 100 hours of use. Refer to your owner's service manual for its location, if you have trouble finding it. Some bottles have an alarm float which can sound your dash buzzer alarm should the fluid level drop too much. In theory this would make it think it's in the clear. If you see no overflow from the vent hole, stick your pinky finger down into the hole and pull it out.
Is there any difference between the Walmart brand Gentech and the Mercruiser brand? What oil do I buy? Water will show up as white streaks in the lube. Good luck but I agree would not mix with anything other than high performance Gear Lube + I'll just add one more vote on not mixing oils. Turn it off, wait a few minutes and remove the dipstick. Oil, Lube and Filters Mercruiser Oil for Sterndrive Engines Changing the oil on a Mercruiser sterndrive is not that difficult. Use your large slotted screwdriver and remove the side vent plug from the side of the upper driveshaft housing. Change the lube every year or sooner if you suspect a problem. Keep a little spare lube in the boat.
Any water at all is not acceptable and if you have water immediate action must be taken to save the drive. Remove the pumps fill hose and install the lower plug making sure the new gasket is in place. Lower gear case oil that resembles the color and consistency of a milkshake indicates water contamination. I can tell you that it's very inadvisable to mix oils. She got loose from the dock with no battery to run the bilge pump. Obviously, it's better to mix oils than run something dry. I have new words now.
If you have an internal Remote Gearlube Reservoir, remove it from it's bracket and pour it out. Look in the bottle and if you see muddy goo or an oily slime, remove the reservoir and clean it out in a parts washer making sure it's clean and dry when complete. In that case if I were you, three options, start driving, call dealer and have them overnight it to you, go to mercruiser website and have it overnighted to you. Wipe up the mess and discard the pan of old lube properly. You might want to try unplugging the sensor in the reservoir; usually they work by competing a circuit when a float drops to a specific level.
Make sure the gaskets aren't stuck on the drain plugs. Place a drain pan directly under the lower unit. Thread the end of the pumps tube into the lower gear housing drain hole and pump the lube into the drive. To create this article, 14 people, some anonymous, worked to edit and improve it over time. . I'm not dumb, as long as an oil is the same weight and viscosity it's interchangeable. Never pressure test a drive while it's full of oil.
Supposedly the Merc stuff can hold a substantial amount of water lots of detergents maybe? MerCruiser is a company that offers sterndrive and inboard engines for boats with horsepower ranging from 135 to 430. I'm out of town and the gear oil for my outdrive is dangerously low. Keep pumping until lube flows out the top vent hole in the upper driveshaft housing. My clear see-thru resevoir is almost empty. Wholesale Marine carries everything you need including Mercruiser oil for your sterndrive.