20HP Model 200 Lower Unit Fill problem

[BlackMax-ThunderToad]

1979 Mercury 20 HP has the normal upper and lower plugs. Drained and began fill from bottom with top screw also out. Can not get lube to come out top hole. There is a 3rd, very small, vent screw aft of top plug at about same level. I opened it and lube came rushing out when squeezing bottle from below. What is the procedure here? Lube never came out top plug hole?

 

[racerone]

The top plug hole may be related to the water pump.--------The small screw is the vent hole for filling the oil.

 

[BlackMax-ThunderToad]

I see what you mean. The exploded view/parts list here on ME says big top plug is "Flushing", small top screw is "grease vent" and bottom plug is "grease filler". Will now check to see I didn't overfill/underfill. What a screwy deal. THANK YOU very much racerone !

 

[BlackMax-ThunderToad]

Filled the L/U and all is well. So now the question is: How is a flush using that hole done? and for what purpose? and do I need to do it?