Hello everyone, (Hope this is the right place to post this) I am wondering, and have for a while, if there is any "real" answers, as to why some people report much lower fuel economy running ethanol mixed gasoline fuel. Math says, that ethanol fuel is lower in BTU's than gasoline, so taking a fuel like "e10", where it is 10% ethanol, should never come close to netting a 10% reduction in fuel economy, but in the real world, myself, and others, have seen DRASTIC mileage improvements switching from e10 regular gasoline, to premium non ethanol gasoline. I realise that with real world driving, there are many variables when driving, like tire pressure, driving habits, etc. But, there seem to be some vehicles, where they seem to get 20-30% better fuel economy, sometimes claiming even higher, on non ethanol fuels. I have read that e10 blended fuels are made using a base gasoline 2.5 octane points lower before mixing, so if it's an 89 octane rating, it would be 86.5 octane rated gas blend, with 10% ethanol added on top, to bring it to an 89 octane rating. One could speculate that it is a low grade gasoline mix to begin with, but I'm not sure how accurate that would be. Gasoline is 115,000 btu/gal Ethanol is 76,100 btu/gal How does e10 end up causing such miserable fuel economy in some engines? Math says if ethanol had 0 btu, mileage could only be reduced by 10%, yet fuel mileage decreases of far worse seem common. Is there anyone that has experience with ethanol mixed fuels, that knows about potential problems, or circumstances that can provide foul burning mixtures, or unintended side effects from these fuel mixtures burning? I realize this isn't a really easy question to answer, as gasoline could be mixed with many different chemicals, detergents, etc depending on brand and location. I also know that most of you would be able to word this question better than myself, and provide better leg work. I calculated 3 of our vehicles miles per gallon, using the odometer, liters added, on the same trips, and premium (ethanol free, less BTU than regular) has netted massive improvements in mileage over the regular gasoline that is e10 mixed. When I say massive, I mean that the extra cost of the premium ethanol free gasoline has more than paid for itself.