Ok..been told that in a 1976 65hp mercury outboard the drain screw in the lower unit is also the fill hole..how does the oil drain?wont there be a vacuum that will hold it in?

https://www.mercurymarine.com/en/us/land/owners-manuals/ https://www.downloadboatmanuals.com/motors/mercury/

I suppose you mean the oil in the Trim system...

Lift the engine all the way up,
Place the jackstand to keep the engine fully up.
You'll see a plastic plug in the center cylinder.
Unscrew that plug. ( There can be some pressure, take care of your eyes!)
Fill with ATF-oil till the level is at the bottom of the plug hole.
Screw the plug back in.
Lower the engine.
Done!

Take out oil drain screw at bottom of gearbox and vent srew above cavitation plate,drain oil,squeeze in oil from bottom till it comes out vent hole,while still holding oil bottle in position screw in vent screw then screw in drain screw

Hi. on the lower unit you will see two screw heads, one above the other. these are the top and bottom openings to the oil reservoir. Since you are probably winterizing I would get a bucket and a flat blade screw driver and drain all of tha old out. Chances are there will be some water mixed in with it. Then get a new bottle of lower unit oil and squeeze it all into the bottom hole while using some force to prevent it from leaking out. Once it is all in, replace the top screw and then the bottom screw. That's it. Happy boating.

4 thumbs up please. Joe

On the lower side of the gearbox,below the line of the prop shaft,you will see a screw that is about10-15mm across.This is the drain for the g/box oil.If you look above that screw about 150mm(6 inches),you will see another screw the same.It may even be marked 'oil level'.Remove them both.
Checked the drained oil is not milky.It's a sign of water and the propshaft seal would need to be replaced.
The oil bottle you buy will have a tapered nozzle.You must fill the g/box from the LOWER hole by sqeezing the bottle.When it comes out of the UPPER hole,the g/box is filled.Quickly put the lower screw back in first,and then the upper screw.Done.
Before you refill the g/box,check the washer/seal on the screws and make sure they are still good. Hope this helps

remove the bottom drain screw first then place a tube of the proper lower unit oil in it. then remove the top screw and gently squeeze the tube of oil and when full it will slowly come out the top drain hole. when it does replace the lower plug first then the top plug second. make sure the seals are in good shape and plan on changing the oil in the lower unit yearly for proper maintainence. make sure you buy oil designed for your particular type of motor. good luck.

There should be 2 drian plug screws on the right side of the lower unit. Remove both of them and let the old oil runout. After it is drained then get some new lower unit grease in a plastic tube and fill the lower unit from the bottom drain hole until it comes out of the top hole. Then you have to QUICLKY replace the bottom screw and then replace the top screw. If the old oil is milky looking then you had water in it. Hope this helps you, Jeepfxr

The bottle that the g/box oil comes in should hve a tapered nozzle.You fill the g/box through the bottom drain hole untill it overflows out the top hole.With both screw plugs removed,squeeze the oil into the lower hole untill it flows out the top hole then reinsert the lower plug first.They dont take a lot of oil but this removes all the air bubbles in the g/box.Hope this helps

to change fluid,take out the bottom plug;should be a flat head screwdriver fitting place something to catch old fluid under the lower unit,then take out top plug,it should drain right out... then from the bottom... fill the lower unit till fluid starts to come out of the top hole then put bottom plug back in, then top plug back in and your good to go..when you have the plugs out check the seals on the plugs and replace if needed...that will insure no water can get in..as far as the fuel mixture you can google that info

The drain/fill hole are the same. Put a coffee can or something like that to measure the amont of oil that comes out. Check with a boat parts, or marine or sporting goods section of biggy store. They (at least to) make a pump assembly with hose and threaded end that fits into the hole for the lower unit screw. the other part of the pump fits in a gear oil quart bottle. 80 or 90 is no matter, but needs to say marine grade or suitable for marine use. Nothing special, Penzoil for sure and I think a company Lubrite plus many others make an OK oil. Anyway, put the pump in the bottle and put back in as much as drained out. The level may be marked on the side of the lower unit. If you don't get almost as much out as you put in, check for leaky seal too.