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I live in a country where unleaded 95 octane fuel is disappearing in favour of its 10% ethanol-blended counterpart: 95 octane E10. The only non-ethanol unleaded alternative is unleaded 98 octanes. Now, I've read up a bit on ethanol and its pros and cons, and am still trying to understand whether or not it is harmful for motorbikes.

Can I use E10 95 octane unleaded in a motorbike? My objective here would be to draft a general purpose comprehensive answer on the topic hence why I am not narrowing this down to one specific make or model.

  • start here : mechanics.stackexchange.com/questions/2295/… – Solar Mike Aug 14 '17 at 6:50
  • Some bikes (Ducati and others) used an ABS type plastic tank for a while and high ethanol content fuels can cause it to warp a little... – Mauro Aug 14 '17 at 7:14
  • additionally, never let a bike sit with ethylated fuel in it, it'll turn into this greenish sludge in your petcock, fuel pump, lines, and carburetors if present that is very difficult to fully clean out. – Ceshion Aug 15 '17 at 16:44
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Ultimately it depends on upon the motorcycle. Here's a couple of things to consider though:

  • Ethanol requires a lower air / fuel ratio to burn, as stated on https://en.wikipedia.org/wiki/Stoichiometry#Stoichiometric_air-to-fuel_ratios_of_common_fuels. Using E10 will effectively lean out the mixture compared to 100% gasoline, which has a higher ideal af ratio. Lean mixtures can lead to overheating, since part of the cooling of the cylinder and valves comes from the fuel itself.

  • Ethanol can cause swelling and softening of some plastics and rubber seals, particularly in older motorcycles that were not designed when E10 gasoline was common.

  • Ethanol absorbs water from air, unlike gasoline. This can lead to separation of the gasoline and ethanol in the tank, with the ethanol/water mix sitting at the bottom. Running solely on the ethanol/water mix will be harmful to your engine. See http://www.boatus.com/seaworthy/SeaApr10Ethanol.pdf.
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Probably yes, but it depends on the make and the manufacturer's specs.

Living in California, I run (state average) E10 91 octane in my 2014 Kawasaki. Runs great. That said, I imagine some bikes (as noted in the comments) may have issue with that. 10% isn't too high, but it really depends.

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Apart from the possible damage to your fuel intake plumbing... realistically you want the highest octane you can get that's approved by the manufacturer. Lower rating means you need more fuel to get the same amount of power.

  • This doesn't really answer the question - the OP is asking if it's safe to use fuel with ethanol in it. – Nick C Aug 15 '17 at 10:26
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It's safe to a degree, apparantly ethanol doesn't agree with fuel pumps and it mixes with any water in the fuel/tank.

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