What is the right fuel mix for my chainsaw?
Your gas chainsaw runs on a fuel mix made up of gas and engine oil. Using high-quality ingredients makes all the difference.
12.11.2024
The importance of using the right fuel mix for your chainsaw
Given that the chainsaw fuel mix powers the engine, it’s no surprise that getting it right is crucial: unsuitable fuels and the wrong mix ratios can cause serious damage, leading to piston seizure, excessive wear, and ultimately a shorter lifespan. We recommend the following mix ratio for STIHL chainsaws with 2-MIX and 4-MIX engines:
If you are mixing the fuel for your chainsaw yourself
1:50 = 1 part oil + 50 parts gas
For example, you can achieve a fuel mix ratio of 1:50 with 5 l of gas and 0.1 l (100 ml) of oil.
Gas
The gas you put in your chainsaw fuel mix needs a minimum octane rating of 90 RON; the gas that is widely available at gas stations is unleaded and rated at 91 RON, which is better for users’ health and the environment too. Use high-quality fuel for best performance.
Engine oil
You should only use high-quality oil for 2-stroke engines, and it should meet the requirements for TC classification. We recommend STIHL 2-stroke engine oil, which is specially formulated for STIHL tools and will prolong the life of your chainsaw. Inferior products can damage the engine, sealing rings and fuel tank of your tool.
How to mix your own fuel
Make up your chainsaw fuel mix in a vessel that is approved for use with fuels – STIHL sells combination canisters that are ideal. Pour in the oil first, followed by the gas; seal the canister and give it a good shake to combine the fuel mixture. Now you’re ready to use the fuel mixture in your chainsaw. Take care as you open the canister, in case pressure has built up inside.
Checklist: mix your own chainsaw fuel
- Use STIHL 2-stroke engine oil or good-quality TC-classified 2-stroke engine oil.
- Mix the oil and gas at a ratio of 1:50.
- Pour both substances into an approved fuel canister and shake the canister to mix.
- Open the canister carefully and fill your chainsaw up with the fuel mix.
- You will find some advice on filling up the tank below.
Checklist: refuelling your chainsaw
- Caution: petrol is extremely flammable, so when handling fuel mix and refilling your chainsaw you should maintain a safe distance from any naked flame, avoid spilling fuel and refrain from smoking. Refuelling should be done at least 3 metres from the working area in which you will start your chainsaw.
- Before you fill the fuel tank, switch the engine off completely; you should not fill it while the motor is hot, as there is a risk of fire if the fuel mix overflows.
- pen the fuel cap carefully so any overpressure dissipates gradually, and ensure that no fuel sprays out of the tank.
- You should only ever fill the chainsaw tank in well-ventilated spaces.
- When filling the fuel tank, take care not to spill fuel mix or get any on your clothes. If you do spill some, you must clean the power tool immediately and change your clothes.
Why it’s best to use chainsaw fuel mix quickly
While a tank of fuel is quickly used up when you’re busy, you may find that fuel mix is left in an idle chainsaw for long periods during the colder months. During these periods, any fuel mix in a canister, fuel tank or carburettor is likely to be infiltrated by oxygen and moisture in the air. This can be detrimental to the fuel mix as it may affect the composition of commercial combustion fuels, potentially attacking and even eliminating manufacturer admixtures such as antioxidants or corrosion protection. These additive components help improve the properties of the fuel.
Resinous deposits
Long storage can also lead to the formation of a resinous “gum”, which is residue left behind when fuel evaporates. Gum in the fuel can give rise to deposits in the chainsaw engine’s combustion chamber, as well as adhesions and blockages in fuel nozzles and filters.
Avoid storing 2-stroke chainsaw fuel mix for more than 30 days
In 2-stroke fuel mix that includes ethanol-containing fuels, the oil and petrol are liable to separate relatively quickly, as ambient moisture binds to the ethanol and sinks to the bottom of the mix. As such, STIHL recommends that you avoid storing 2-stroke chainsaw fuel that you mix yourself for more than 30 days, in order to minimise separation.
Watch out for separation in your fuel mix
Once it separates, your fuel mix no longer has an even distribution of 2-stroke engine oil throughout it, so you cannot be certain that the engine is properly lubricated. Insufficient lubrication and cooling could cause problems in the functioning of your chainsaw, or even piston seizure. A separated fuel mix is no longer a correctly mixed product, even if you shake it vigorously.
I used the wrong fuel in my chainsaw, what shall I do?
If your fuel tank contains an incorrect fuel mix, you must not use the chainsaw at all – even for a short time. Use a funnel to empty the tank and pour the incorrect fuel into a safe canister, then fill the tank with the correct fuel mix. Though this is generally enough to remedy the issue, if you find the chainsaw doesn’t start you may need to also clean the spark plug.
Operating manuals for STIHL chainsaws
You can download the operating manual for your STIHL chainsaw here at your convenience.
Summary: chainsaw fuel mix
- Always ensure that the components of your petrol-oil mix are good quality.
Make sure you use the right mix ratio: in 2-stroke engines, 1 part engine oil to 50 parts petrol.
E10 petrol can be used in STIHL and VIKING tools.
Storage periods vary depending on the mix. A mix you have made yourself may no longer be fit for use after 30 days of storage.
The safe and easy choice is to use ready-mixed STIHL MotoMix in your chainsaw
