Reader Question: To Ethanol or not Ethanol?

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Here’s the latest reader question, along with my reply!

Bill asks: Hi again Eric! I own cars until they go no longer. I suppose I am asking for answers specifically for people like me. If buying gasoline with ethanol up to 10 percent of it, in general, you wouldn’t recommend filling up with a higher octane gas, would you? Additionally, again in general, is ethanol-free gas worth a 30 percent premium over ethanol-infused? Thank you in advance for your experience and wisdom.

My reply: I wouldn’t spend money on higher octane gas – whether E10 or E0 (no ethanol) if the engine doesn’t need the higher octane. The ethanol content is irrelevant as regards this question as octane is a separate matter.

Go with the manufacturer’s octane recommendations (see the owner’s manual or the sticker on the inside of the gas door). Using higher than necessary octane fuel (whether E10 or E0) won’t improve either performance or fuel efficiency if the engine isn’t designed for high octane fuel. In fact, you may experience a reduction in mileage and power/performance – and you will certainly be paying more for the higher-octane gas!

The reverse is also true – and potentially worse – if your vehicle is older and doesn’t have computer-controlled engine management and so the ability to automatically adjust for lower-than-specified octane, which could otherwise pre-ignite from heat and pressure rather than spark in the cylinders; this places great stress on the pistons/rods/bearings and so on. But it is largely not a problem anymore as pretty much all cars made since the early ’90s will self-adjust of fed lower-than-specified octane fuel.

As far as the rest: The extra cost of the ethanol-free gas is worth it, in my opinion, for older vehicles that were not designed for ethanol-laced gas – this is mostly vehicles made before the mid-1990s – and also for power equipment, especially power equipment that may sit for months at a time. Ethanol does not store as well as “pure” gasoline. Regardless, I recommend shutting off the fuel valve (install one if the machine in question didn’t come with one) and running the engine until it dies; this will reduce the odds of fuel congealing into goo over the period of time the machine is in storage.

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  1. I used to keep a gallon or two of octane booster on hand. Often the gas stations at lakes have high octane fuel since so many boats require it. It would be slightly higher but not 30% for sure.


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