I think making it use alcohols is a bad solution in that it trivializes fuel sourcing and makes bio-diesel essentially obsolete, as bio-diesel is the further processed form of alcohol specifically for fuel usage. In this case, I'd say we eschew realism and make gasoline engines also run off bio-diesel, to prevent gasoline from becoming the new best option by a landslide because you can loot alcohol everywhere, and process the base materials into the above options without much work.

Diesel engines will still be better than gasoline engines by dint of being more efficient, but this way it both solves the issue of gasoline engines not having alternatives the player can source while also not turning gasoline engines into a no-brainer "best" option, especially considering that most engines in the game are gasoline engines.

Not sure I like the idea of using biodiesel. Burning ethanol in stock unmodified gas engines may be an acceptable stretch, but this is downright unrealistic.

And as for using spirits being unbalanced: sure you can find them everywhere, but in what quantities? If we're talking about regular alcohol, it still needs to be distilled to make usable, greatly reducing the initial volume. Biodiesel, on the other hand, is 100% processed fat. Alcohol is used in its production as a reagent, not as a burnable substance, and in relatively small quantities. Personally I'd still prefer using biodiesel even with ethanol as readily available fuel because of how much easier it is to source large amounts of oils/fats.

EDIT: while I endorse the initial idea of enabling use of distilled spirits as fuel, methanol should not be included as it is corrosive and should not be used in combustion engines. So, only ethanol should really be usable, making the whole thing even less of a balancing concern.

Worth noting that while plain alcohol is in abundanance, ethanol takes additional time, resources, and tools to set up.

It also has like half the fuel value of biodiesel: https://github.com/cataclysmbnteam/Cataclysm-BN/blob/upload/data/json/items/fuel.json#L21

I would say that should've been a reasonable tradeoff for the method to make it being overall simpler (but not really dead simple) than biodiesel.

Makes this mods obsolete, no? https://github.com/Valikdu/Valik_Vehicle_Expansion , at least the ethanol engines.