Two vent holes on Mariner lower????

[LaveyT]

Just got done winterizing the ol Houseboat for the first time.The 1989 mariner lower has two vent screws in the lower,one inline with the driveshaft (aproxx) and the other by the shift rod?What is this front screw for?

[Greg Moss]

Some of the older Mercs and mariners had a vent screw under the water pump base. It is actually a flush port. Most do not work anymore because if the water pump base was changed the new ones don't have the pport cut into the base.

[LaveyT]

Its a 1989 75h.p. 3cyl.Both screws were on the same plane in "Z" axis.The one in towards the front of the unit is the one that has me puzzled?

[Greg Moss]

Got a serial number?

[sosmerc]

The "forward" upper screw is a gearcase oil vent. To drain gearoil, remove the lower screw and both of the upper screws.
Fill from the bottom until you get oil to run out of the forward vent screw. Re-install the forward vent screw and continue filling until oil runs out the vent screw that is in the upper middle area. By the way, whenever changing gear oil is it a good idea to replace the gaskets. When done, I give them a pretty good "tap" with an impact screw driver to sort of compress the gasket. (a manual impact hammer....NOT an air driven tool!). Also, Merc now uses a gasket that appears to be made out of a better material...it is sort of orange in color and feels almost like rubber....I still plan on replacing whenever checking or filling gearcases.

[Greg Moss]

Omc has the best gasket. It is made out of nylon the number is 311598 they are a lot better than the Mercury gasket.

[LaveyT]

Thank you guys.Thats not the way I did it,Gotta get some more lube.I thought they both looked like vents!That little Mariner has been real good to me so far,a little lube is the least I can do!