Mixing Oil & Gasoline for Two Stroke Outboards

Last Updated on June 4, 2025

Mixing oil and gasoline for two-stroke outboard motors can be tricky, but it's a must for keeping your engine running right. This guide will walk you through the steps, from picking the right gas and oil to using a measuring device, so you can confidently fuel your two-stroke engine.

Getting Started: Fuel and Additives

When you're dealing with two-stroke outboards, especially older models or if you're using gas with ethanol, a few things are important. First, always use fresh gasoline. This helps a lot, especially with ethanol blends. Second, add a fuel stabilizer. This is a big help for fighting the problems that ethanol can cause in your fuel system. There are different brands out there, but something like Sta-Bil 360 Marine works well.

Understanding Oil-to-Gas Ratios

One of the most important parts of fueling a two-stroke engine is getting the oil-to-gas ratio right. This ratio tells you how much two-stroke oil to mix with your gasoline. Different engines need different ratios. For example, a newer two-stroke might need a 100:1 or 50:1 ratio, while an older engine, like a 1958 Johnson Sea Horse, might need a 24:1 ratio. Always check your engine's manual to find the correct ratio.

Using an Oil Measuring Container

These containers can look a bit confusing at first, but they're really helpful. Here's how to read them:

Top Row: This usually shows the different oil-to-gas ratios (e.g., 100:1, 50:1, 24:1).
Table: Below the ratios, you'll find a table that helps you figure out how much oil to add based on the amount of gas you're mixing.

Let's say your motor needs a 50:1 mixture, and you have 5 gallons of gasoline. You'd find the 50:1 column, then go down to the row for 5 gallons. The container will have a mark indicating how high to fill it with oil for that specific amount of gas and ratio. If you're mixing a larger amount of gas than the container can measure at once (like 10 gallons for a 24:1 ratio), you might need to fill the oil measuring container twice.

Mixing the Fuel

Once you have your fresh gas, stabilizer, and two-stroke oil, it's time to mix. For a 1958 Johnson Sea Horse 3 horsepower outboard, which uses a 24:1 mixture, you'll need to be precise. If you're unsure of the internal tank size, it's a good idea to measure out your gas first. For example, if you're mixing one gallon of gas:

Measure your gas: Pour one gallon of gas into a separate container.
Add stabilizer: Put the recommended amount of fuel stabilizer into the gas. The bottle will usually have instructions for how much to add per gallon.
Measure oil: Using your oil measuring container, fill it with TCW3 two-stroke oil up to the mark for a 24:1 ratio and one gallon of gas.
Combine: Pour the measured oil into your gallon of gas.
Mix well: Give the mixture a good shake or stir to make sure the oil and gas are fully combined.

Fueling and Starting Your Outboard

Now that your fuel is mixed, you can add it to your outboard motor. For an engine with an internal fuel tank, like the 1958 Johnson Sea Horse 3, the tank is usually on top. Make sure to open the air vent on the tank to allow air in as the fuel goes in. Also, open the gas valve.

Before starting, check your engine's instructions. For the Johnson Sea Horse 3, you might need to:

Set the Magneto lever to the start position.
Pull the choke out.
Adjust the high-speed lever as needed once the motor is warm.

With the right fuel mix and proper starting procedure, your two-stroke outboard should be ready to go. Getting the mix right is key for engine longevity and performance, so taking the time to do it correctly is always worth it.