Chainsaw fuel mix: What is the right chainsaw fuel ratio for my chainsaw?

The importance of using the right chainsaw fuel mix

Given that the chainsaw fuel mix powers the engine, it’s no surprise that getting it right is crucial: unsuitable fuels and the wrong chainsaw fuel mix ratios can cause serious damage, leading to piston seizure, excessive wear, and ultimately a shorter lifespan. 

The right chainsaw fuel mix ration - What you need to know if you are mixing the fuel for your chainsaw yourself

We recommend the following mix ratio for STIHL chainsaws with STIHL 2-MIX and STIHL 4-MIX engines:

1:50 = 1 part oil + 50 parts petrol

For example, you can achieve a fuel mix ratio of 1:50 with 5 l of petrol and 0.1 l (100 ml) of oil.

Petrol

The petrol you put in your chainsaw fuel mix needs a minimum octane rating of 90 RON; the petrol that is widely available at UK petrol stations is unleaded and rated at 95/97/98 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 chainsaw fuel mix 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.

Chainsaw fuel mix DIY: 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 petrol; seal the canister and give it a good shake to combine the fuel mixture. Now you’re ready to use the chainsaw fuel mixture in your chainsaw. Take care as you open the canister, in case pressure has built up inside. 

The right fuel – no mixing required

The easy way to give your tools the best treatment is by opting for STIHL MotoMix fuel, a premixed chainsaw fuel mixture that is specially formulated for our tools and guarantees high performance and a long service life.

What is E10?

E10 designates petrol that contains up to 10% ethanol. Premium-grade petrol has a maximum ethanol concentration of 5%.

2-stroke chainsaw fuel mix 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 petrol 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.

Video: how to fill a chainsaw with fuel mix

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 chainsaw 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 chainsaw 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 chainsaw fuel 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