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Mercruiser oil fill screw - upper gearcase part

Upper gear housing vent plug

  • GLM part 22420
  • OEM 10-79953Q2
  • Tech support Exploded view drawings
  • Includes 1 gasket separate 5 pack gaskets are also available

22420 Vent Screw Plug 10-79953Q2

22420 Vent Screw Plug 10-79953Q2

P/N 22420 Vent screw. Replaces 10-79953Q2 or Sierra 18-2244. $5.99

Oil Fill Instructions Lower Unit

Oil Fill Instructions Lower Unit


How to Instructions for Filling the Stern Drive with Oil

The gear housing oil circulates both through the upper and the lower unit. Make sure to only use the lower drain fill hole to pump the lubricant in.

After draining all the fluid, begin by removing the vent screw on the starboard side of the upper housing.

Note – if you notice an excessive amount of metal filings in the lube, or if the lube is milky in color this indicates some damage to the internal mechanical components or water leaking into the case.

These are both issues that must be addressed immediately as they could lead to partial or complete outdrive failure. Fill the lube through the lower drain hole until it begins to come out of the upper vent screw.

Never fill the case from the upper vent screw down as this will allow for air pockets to travel down, creating a false reading on the oil level.