A while back I tried using E85 in an old chainsaw, I blew the rod almost instantly, I assumed this was due to the alcohol needing more lube oil mixed in the fuel - well - Sorta, but not the root of the problem.

I got tired of arguing with a stubborn chainsaw today and took a break and did a simple E85 fuel experiment. On my other attempt to run E85 in a chainsaw I mixed the fuel/oil in a normal red opaque plastic 1 gallon fuel jug, today I used a clear 2-liter soda bottle, much to my horror the oil started to settle out of the E85 almost instantly, within 5 minutes almost all the oil had settled out.

This test uses 4 oz of new Walmart blue 2-cycle oil, the 4 ounces equates to a 16-to-1 fuel/oil blend, this is a lot more oil than newer saws require but my old saws run fine on it and it adds some margin of safety for lubrication, but only if the oil stays blended.

I repeated this test using 4 oz of clean used veg and the oil has not settled out at all but it has only been a few hours. Model airplane fuel is basically methanol and veg oil (caster oil, lubes rather than burns due to it's high ignition temp) so I don't expect this eth/veg blend to separate, I will give it a try in the saw and see if it survives. Using soy oil in the blend may cause a bit more spark plug fowling but maybe not?

I had done some blend tests with E85 and used engine oil, the oil settled out of those too, I should have realized it would also happen with petro-based 2-cycle oil.

That's not the only problem with ethanol blends, if the fuel gets moisture in it which is more likely because of the ethanol, the ethanol water mix separates from the hydrocarbons.

Most model airplane fuels use synthetic oil. Castor oil hasn't been popular since the 1960's or so. The synthetics don't leave the deposits that Castor oil did. Note also that the Castor oil used in fuel isn't the same as the castor oil sold in drugstores. Some motorcycle shops still sell castor oil, preferred by some old 2-stroke customers.

The oils that ARE used in model fuel may not be the same as Walmart Blue 2-stroke oil. It might be worth researching it more.

I've read in other threads that E85 (and even straight ethanol mixed with gasoline) will drop it's lubricant load when the ethanol absorbs enough water. If true, then the trick is to keep the fuel "dry" in storage and use. Alternatively, a lubricant is needed that stays in solution even if "wet". Perhaps that's what model airplane fuel uses?

Cheers,
JohnO

Does biodiesel provide enough lubricity for a 2-stroke? It may not separate out as readily.