What Is the Gas Ratio for Outboard Motors?

Outboard motors are common on pleasure boats of all types.

Outboard motors need to be well lubricated because of the power-to-weight ratio in their design. If the motor does not have a oil reserve function, then the outboard motor uses a 50-to-1 gas/oil mixture.

Certified Motor Oils

Two-stroke outboard motorboat owners should only use motor oil that is certified by the National Marine Manufacturer's Association with a qualified rating of TC-W3. The NMMA certification is a specification used in United States but other countries do use this certification as well.

Gas-to-Oil Ratio for Pre-1980 Motors

Outboard motors use gasoline and oil at the same time. Most two-stroke outboard motors made before 1980 use a 50-to-1 ratio of gas to oil. It is much simpler to use a larger tank to mix appropriate amounts of oil and gas. For a typical, 6-gallon gas tank, you would add about 16 oz. of oil.

Newer Outboard Motor Mixture

Two-stroke outboard motors made after 1980 generally rely on an oil reservoir located on the motor. The reservoir mixes the oil and gas automatically when the motor is running. The oil reservoir should always be checked and filled and when starting the motor. Four-stroke outboard motors also mix oil and gas with the reservoir system.

References

• Tohatsu Outboard Motors: Tohatsu Marine Oil/Gas Mixture Chart
• "Lubrication Fundamentals"; D. M. Pirro, A. A. Wessol, J. George Wills; 2001
• Tohatsu Outboards: Oil/Gas Mixture Chart
• "Power Boating for Dummies"; Randy Vance; 2009
• National Marine Manufacturers Association: TC-W3 Two-Stroke Oil Certification Program