Doc Octane plots against us

And he leaves behind a dilemma:

It took a while to burn up what low-octane, ethanol-containing fuel was still in the system, but once it did, the tractor’s engine suddenly ran smoother, and the sputters all but all but disappeared. So now I know that either the ethanol or the low octane in the other gas is what was causing the trouble. I just don’t know which.

Premium runs for well over $3 a gallon around here, which isn’t great, but still better than $4 a gallon. If the octane is the determining factor, less expensive, slightly-higher-octane premium gas would be better. It took running a lot of the regular through this tractor to make the trouble appear, so if I were to experiment I’d need more than a gallon, but preferably less than a full can.

The manual might tell me ethanol is the culprit, but I’ve read that about all lawn-mower engines — and this is the only one — walk-behind or riding — that’s ever had trouble with the grade of fuel I put in it.

The deleterious effects of ethanol, as I understand them, are cumulative over long periods of time: seals and such deteriorate. I would not want to extrapolate from automotive experience, since almost all modern-day cars and/or trucks are able to fiddle with ignition timing to compensate for octane rating, something I suspect is not true of lawn tractors. But this sentence may give it away: “It took running a lot of the regular through this tractor to make the trouble appear.” Which implies an almost-empty fuel can, which in turn implies some sort of heavier-than-gas gunk that sank to the bottom of the can.

An experiment suggests itself: get some 87-octane E-zero, if it’s anywhere nearby to be had. (Locally, it’s about $2.90 a gallon, 35 cents or so higher than 87 E-10.) Interestingly, 91-octane E-10 runs about $3.10, but I’ve been paying $3.219 for 91-octane E-zero, and using 5 percent less of it.


  1. fillyjonk »

    7 October 2018 · 2:10 pm

    FWIW, the small-motor repair place my parents take their lawnmower to (not lawn tractor, lawnmower) strongly advise for 100% gas (no ethanol). I think that’s true of a lot of smaller motors…

    I wonder if also leaving gas sitting in a tank (few people run their lawn tractor daily, though one of my neighbors seems to mow every other day) has some effect you don’t see with a car that’s used regularly. (So: if a car is going to sit for some days to weeks, maybe no-ethanol gas along with any other precautions?)

    I can get allegedly E-zero gas at the Love’s (they do warn, as it’s a shared hose, the first few gallons may have residual ethanol). I don’t, because I’m kind of skint right now and the 40-to-50 cent difference is kind of a lot. I just hope I don’t pay for it bigger later on.

  2. McGehee »

    7 October 2018 · 5:36 pm

    The canful on which the trouble arose was not the first, and the one I finally emptied wasn’t the same canful.

    I’ll use stabilizer solution over the winter (though again, no other mower ever complained about the gas).

    I don’t know why E0 is so expensive here, unless there’s an EPA thumb on the scale due to air-quality rules.

  3. CGHill »

    7 October 2018 · 6:37 pm

    That would not surprise me. EPA largely leaves us alone, since we manage to squeak by the air-quality standards each year.

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