For the 80 hp Mercury, you may use any brand of gear oil that has been blended for use as an outboard motor gear lube. There are many brands available other than oem, and are specially formulated for outboard use.
The 1973 model, 7.5 hp Mercury outboard, requires 6.8 oz. of gear oil.
The speed of a 12hp engine in mph depends on various factors such as the weight of the vehicle, the gear ratio, and the aerodynamics. Generally, a 12hp engine can propel a small vehicle like a go-kart or a lawnmower to speeds ranging from 20-40 mph. However, for a more accurate estimation, a specific vehicle and its characteristics would need to be considered.
The 5 hp Mercury outboard requires no special type gear oil. General recommendation is for a GL-5 class lubricant, i.e. hypoid 90w. Most any of the oem, or aftermarket gear lubes, manufactured for outboard use, will work just fine.
outboard motor will start and idle, but dies out under load
22.5 fluid ounces (or 666 ml's) per our 1994 Mercury 125 outboard manual.
If the horsepower of your Mercury outboard lower unit is 75 and below, SAE 80W90 Gear Lube is recommended.
what causes a boat motor 40 hp to stall when it is put in gear
Mercury® Marine High-Performance Gear Lube from Basspro
398lbs +prop and oil,gear lube 446lbs
The gearcase assembly on an outboard engine is sealed, and draining is not needed. If however, the gear lube has not been changed in a while, during the water pump replacement is generally a good time to do so.
I had used a high performance gear lube quick silver marine lubricant it is not expensive and works very well