Mixing Fuel and Oil – Older 2 Stroke Outboards

Mixing Fuel 1

If you have an older 2 stroke outboard, it’s a fair bet you have to mix your fuel and oil yourself. After bad experiences with first generation premix systems, many anglers also disable them on newer motors, preferring to mix their own fuel.

Calculating the amount of oil to add can be a bit of a headache, especially if, it’s been a long time since you were in a maths lesson. The amount of fuel you need to add to top up a tank also complicates the equation because it is never a nice round number like 10, 20 or 50 litres that allows you to calculate the amount of oil to add easily.

Getting the maths wrong can be disastrous; too much oil and your motor will smoke and probably splutter and cough as the plugs oil up. Too little oil and you run the risk of the motor overheating and doing expensive internal damage.

Mixing Fuel 2

Here is a small equation even the most mathematically challenged can do in their head.

It calculates the amount of oil required for a ratio of 50:1 which is the ratio used by the majority of older motors.

Before using this equation, make sure your motor uses an oil mix of 50:1.

When you have finished filling your tank, look at the amount of litres you have added.

To calculate the amount of oil required, double the litres, add a naught and call it millilitres.

Let me give an example: You added 13 litres of fuel to your boat tank. The equation is 13 x 2 = 26. Next you add a naught = 260 and you call that millilitres.

So the amount of oil required for a 50:1 mix in 13 litres of fuel is 260 millilitres.

A simple system that removes the guesswork and calculator when refuelling older 50:1 2-stroke motors.


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