To change the oil on a 3 HP Mercury outboard, first ensure the engine is turned off and cool. Remove the oil drain plug, typically located at the bottom of the gear case, and allow the old oil to fully drain into a suitable container. Replace the drain plug, then use a pump to add new oil through the fill hole until it reaches the appropriate level, checking with the dipstick if available. Finally, securely replace the fill cap and dispose of the old oil properly.
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The 1977 model, 20 hp Mercury outboard, requires a 50:1 fuel to oil ratio.
What is the fuel to oil ratio for a mercury 9.9 hp 2 stroke engine?
If manufactured after 1965, an 80 hp Mercury outboard requires a 50:1 fuel, to 2 cycle oil ratio.
The 1973 model, 7.5 hp Mercury outboard, requires 6.8 oz. of gear oil.
50:1
In the fuel tank
A 25 hp Mercury outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
The 20 hp Mercury outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
The 4 hp Mercury requires a 50:1 ratio, roughly one pint of 2 cycle oil, to six gallons of fuel.
The 2.5 hp Mercury outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.