Will my STIHL chainsaw work with E10 fuel?

You may have seen or heard that this new fuel will be replacing existing 95 ron fuels during the summer, we are increasingly being asked about E10 fuel and it’s compatibility with petrol driven equipment, particularly STIHL chainsaws we’ve supplied.

What is E10?

E10 is a mixture of conventional unleaded petrol and ethanol. E10 means it is 90 per cent petrol and 10 per cent ethanol.

What is ethanol?

Ethanol is an alcohol-based fuel produced from the fermentation of a range of plants including sugar cane, wheat, corn, sorghum and barley.

The simple answer is it won’t really change things very much. we’ll explain why, but first it’s necessary to have an understanding of the issues that ethanol causes in fuel.

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Ethanol is hydroscopic meaning that it attracts moisture. This creates a problem in petrol machines because if left for a couple of months (sometimes as little as a few weeks) the ethanol content attracts moisture into the fuel – this is why you see condensation on the inside of a fuel can that’s been left unopened for a while. This stale fuel then ends up being used in a machine. The same thing happens to fuel that’s left in a machine. Even if you drain the fuel out of the tank before storing it, there will still be fuel left in the carburettor which will attract that moisture.

So whether it’s from a can, or fuel left in a machine the moisture ends up in the engine one way or another unless you run the engine dry before storage.

Once inside the carburettor the moisture will block things up – if you’re lucky, a droplet if water will form and will block gauze filters, requiring the carb to be dismantled to clear this out. Usually though, in addition to water droplets/blockages it will cause oxidisation inside the carburettor which form more serious blockages in the microscopic jets and drillings inside the carburettor. These can sometimes be shifted with cleaning and an ultrasonic cleaner, but more often than not it just dislodges it to another place in the carburettor, the only solution being a replacement carb at significant cost.

STIHL Motomix FuelAll of the above is only an issue if the fuel is stored or left sat in the machine for longer than a few weeks and allowed to go stale. If it is regularly used up, replenished with fresh fuel and never allowed to sit for weeks on end then there should be no issue, whether it’s 5% or 10% ethanol content.

From an engine running perspective, there should also be no impact if the fresh fuel is mixed correctly. STIHL machines such as chainsaws are designed to be run on 2-stroke fuel in a 50:1 fuel to oil ratio if used with their own 2-stroke oil. The engine gets it’s lubrication from the oil that’s added, not from the neat fuel and the percentage ethanol content will not change this.

Check the operator’s manual for confirmation, but in summary, STIHL M-Tronic engines are ok with up to 25% ethanol and their non-M-Tronic engines (manual carb adjustment) can cope with up to 10%. It’s also worth noting that E10 fuel been used across Europe, the US and Australia for years now without problem, so long as the above precautions are adhered to.

To avoid any confusion, difficulties in mixing or storing fuel we’d simply recommend using STIHL’s own MotoMix pre-mixed 2-stroke fuel (available from Southern Power Tools).  It’s available in 1L, 5L, 55L or 200L quantities. Not only is it completely ethanol free so it won’t attract any moisture but it also has added fuel stabilisers giving it a 5yr shelf life. This means that it can be bought and left in the can or in the machine for long periods without the need to drain or run the machine dry. It also has STIHL’s highest quality of 2-stroke oil (HP Ultra) pre-mixed in and an extremely low ‘ash’ content, so the combustion is very clean, all of which is great for the longevity of the engine too.

We’d also recommend having a read of the latest STIHL blog which covers this topic quite nicely: https://blog.stihl.co.uk/how-will-e10-petrol-affect-your-stihl-chainsaw/

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