Last Updated on February 28, 2022 by Grow with Bovees
Most hand-held outdoor power tools these days use a 2-cycle, 2-stroke engine and that means using gasoline combined with oil mix in the tank rather than just fuel on its own.
There are so many mixing ratio numbers though, and it can be difficult to keep track of what to use in your own machinery.
The 50 to 1 ratio vs 40 to 1 doesn’t sound like much of a difference but you will need to know how to mix the correct quantities if you need to make up different batches.
If you don’t get the mixture right you could cause engine damage on your leaf blower or string trimmer, or at the very least cause it to run too lean or too rich, so here at Bovees we decided to create a simple guide to tell you all you need to know.
What is a 2-Cycle Air Cooled Engine?
First of all, we thought it would be a good idea just to run through what a 2-stroke, 2-cycle engine is and why it needs to run on a gasoline/oil mix rather than just petrol alone.
Developed in the late 1800s, a two-stroke (or two-cycle) engine is a type of air-cooled internal combustion engine that completes its cycle with two strokes or up/down movements of the piston and one revolution of the crankshaft.
In contrast, a 4-cycle engine uses four strokes of the piston to complete the same power cycle and takes 2 crankshaft revolutions.
2-stroke power engines benefit from a much higher power-to-weight ratio plus have fewer moving parts than a 4-stroke engine.
This makes them very lightweight, powerful, and robust, and ideal for use in many popular yard tools such as chainsaws, gas powered weed eaters, backpack blowers, pole saws and brushcutters, plus lots of other equipment.
As we know, 2-cycle air-cooled small engines run on a petroil mixture which is a blend of gasoline and oil that provides both fuel to burn and lubrication at the same time.
This means they have no separate oil sump and makes them a very flexible power source as they can be mounted and run in any position, even upside down!
Working Out What Mixing Ratio to Use For Your 2-Cycle Engine
The easiest way is to check the manufacturers’ instructions, owner’s manual or any labels on the engine/tool for a clue on what mixture to use.
If you can’t find anything then try to identify when your equipment was likely to have been made. Usually, the year of manufacture is stamped on the engine label somewhere near the model number.
This gives us an indication of what mixture to use:
For 2-stroke handheld machines manufactured before 2003:
Use a 32:1 gas to oil ratio. That equates to one gallon of gasoline mixed with 4 oz of 2-cycle engine oil which is too much oil for more modern machines.
Note: If you live in California, because of emission laws, just use a gas to 2-cycle oil mix ratio of 40:1 whatever the age of the engine.
For 2-cycle handheld tools manufactured from 2003 onwards:
Use a 40:1 gasoline to two-cycle oil mix ratio. That means your mixture of gasoline will be one gallon of petrol with 3.2 oz of 2-stroke engine oil.
What about if you just don’t know the age of your engine?
The safest option is to use the 40:1 two-cycle oil mix ratio. Pretty much all two-cycle leaf blowers and string trimmers in use today will run on that without too much of an issue.
However, many modern engines run on a 50:1 ratio, so if you have a newer machine, check the manufacturers website or ask their customer service department what fuel mixture to use.
Preparing to Mix the 2-Cycle/2-Stroke Engine Oil and Gas Mixture
You will need a gasoline can or other suitable container and a measuring jug.
First of all, make sure your gasoline can is empty so that you don’t mess up the mixing ratio with the wrong proportions.
Measure out and add your two-cycle engine oil to the empty can before adding a gallon of fresh gasoline. There’s no need to agitate the mixture, it will merge by itself doing it this way.
Bear in mind that many machines only have a one-gallon gas tank, so only prepare as much as you need for that day.
If the mixture needs to be stored for longer than 30 days, it would be an idea to add a fuel stabilizer additive, such as Seafoam or Stabil to the gallon of gasoline combined with oil mix to help increase its shelf life. Don’t use too much stabilizer though, you only need a small amount.
If the can has been stored for more than 30 days, give it a bit of careful shake to stir it up again before use.
Finally, make sure you label the can so that you know it contains your fuel/oil mix and avoid engine damage by putting it in your 4-cycle lawn mower for example.
Important note: Gasoline with an ethanol content of greater than 10% can damage your carburetor and cause engine failure if not stored properly, so we recommend you avoid that type of product. This is because Ethanol will attract moisture when exposed to the air and that could cause the mixture to separate.
How do you prepare a 32 to 1 ratio?
It’s not too hard to achieve the correct oil with fuel mix when aiming for a 32:1 ratio.
Just take care when measuring to get the right quantities.
First of all of course, purchase the desired amount of gasoline and some good quality 2 cycle oil.
Choose a well ventilated area away from open flames to do your mixing.
To achieve a 32:1 mixture, use 4.0 ounces of oil per 1 gallon of gas.
For two gallons of gasoline use 8 ounces of oil and so on.
For metric measurements, this equates to 156 ml of oil to 5 liters of unleaded gas.
Making a 40 1 Fuel Mix
With a 40 to 1 mixture you will be using less oil per gallon of gas.
Once you have your fuel and oil and are ready to go use the following quantities:
If you have 1 gallon of gas, use 3.2 ounces of engine oil.
If you want to make up 2 gallons worth then it’s 6.4 oz of oil to your 2 gals of gas.
For metric users, this works out at 125 ml of oil to every 5 liters of gas.
10 liters of gas would need 250 ml of oil for your 40 to 1 mix.
How to Make a 50 1 Fuel Mix
With a 50 to 1 mix ratio vs 40 to 1 oil mixture, we’re using a little less oil (more parts gas to oil).
For a 1 gallon mixture use 2.6 fluid ounces of oil for one gallon of gas.
That means two gallons will need 5.1 oz of engine oil.
On the metric scale you will need 100ml of oil for 5 litres of gas.
10 litres of petrol will need a maximum amount of 200ml of oil for a 50:1 ratio.
2-Stroke Oil Mix Quick Reference Calculator
As a summary, here’s a quick ready reckoner for mixing the 3 main ratios:
U.S Measurements
For a 32:1 ratio, use 4 fluid ounces of 2-stroke oil mixture per gallon of gas.
40 to 1 Ratio per Gallon
For a 40:1 fuel mixture, use 3.2 fluid oz of oil per gallon of gasoline.
50 to 1 Gas Mix For 1 Gallon
For a 50:1 mixture of gas to oil, use 2.6 oz of oil per one gallon of gas.
Metric Measurements
For a 32:1 ratio, use 156 ml of 2-stroke oil per 5 litres of petrol.
40 to 1 Fuel Mix For 5 Litres
For a 40:1 mixture, use 125 ml of oil per 5 litres of fuel.
50 to 1 Fuel Mix For 5 Litres
For a 50:1 mixture of gas to oil, use 100 ml of oil per 5 litres of gas.
Final Thoughts on 40:1 vs 50:1
Does 40 to 1 have more oil than 50 to 1?
As we mentioned earlier, many gasoline powered tools on the market today use a 50:1 ratio which contains slightly less oil than a 40 to 1 mix.
If you’re unsure what the mixture of fuel used is in your machine then it’s better to run rich (i.e. have more oil per ounces of gas) than to run lean (less oil in your fuel system) so we would go for the 40:1 ratio as the ideal fuel mix.
When it comes to choices of fuel for your two-cycle engine hand-held equipment it’s best to run your engine on gasoline that has a minimum octane rating of 89. Gas with a lower rating can decrease engine life due to running at higher temperatures.
If you’re unsure about the measurement of fuel or how to get the right mix to ensure the best engine protection, you can buy pre-blended fuels which although more expensive in the long run, are very convenient and easy to use.
References:
https://www.stihlusa.com/information/how-to-guides/mixing-oil-and-gasoline/
