Your petrol chainsaw runs on a fuel mix made up of petrol and engine oil. Using high-quality ingredients makes all the difference.
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:
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.
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.
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.
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 fuel mixture in your chainsaw. Take care as you open the canister, in case pressure has built up inside.
Petrol that contains up to 5% or 10% ethanol is generally suitable for use in all STIHL chainsaws and power tools, as well as STIHL gardening tools that have Briggs & Stratton, Kawasaki and Kohler engines.
You may find you need to readjust the carburettor to compensate for the changed composition of the fuel. We recommend that you consult a STIHL dealer in this instance.
E10 designates petrol that contains up to 10% ethanol. Premium-grade petrol has a maximum ethanol concentration of 5%.
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.
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.
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.
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.
You can download the operating manual for your STIHL chainsaw here at your convenience.
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