1977 Mercury 7.5 Horse Lower Unit Oil amount

[boat-novice]

As my login name says, I am a boat novice and not very mechanical, so pardon me if my simple questions insult anyone. First, I am attempting to change the lower unit oil. I don't have the manual for my 1977 7.5 horse mercury outboard and I am unsure how much oil should go in it. I know I am supposed to put oil into it until it oozes out the vent hole, but any rough idea of how many ounces that is?

Also, while draining the old oil, it came out a milky color (which I know means water) and it is coming out thick, almost like molasses--the screw gaskets were rotted, so I am hoping new gaskets will solve the water issue. How do I know if I have drained all the old gunk out? I am leaving it drain overnight. Can I pump air through the vent or will that cause problems?

What does the screw hole titled "flush" do?--it is just below the cowl on the shaft.



Thanks for all the help!

 

[86RajunCajun]

Re: 1977 Mercury 7.5 Horse Lower Unit Oil amount

All you will need is one bottle of gear lube most likely. Fill from the bottom hole till the gear lube flows out the top hole and seal it up.

As far as draining the old gear lube water mix out, i would let gravity take its tole over night with the plugs out, then i would fill the lower unit with fresh gear lube, run it once on the water, and then flush the gear lube again.

Running it with fresh oil in it will scrub out the inside and get more of the old water oil mix off the walls of the unit, then you drain it and it all comes out with the oil. Fill again with fresh gear oil and you should be good to go.

The plug titled "flush" is just that, a flush plug hehe. I think it is for the cooling system to flush it out.

GL

RC