I'm not a car expert but I remember hearing somewhere that it depends on how the engine is manufactured. Here in Brazil the car engines are engineered to withstand high alcohol contents and there are even cars with "flex-fuel" technology that can handle any mixture from 100% gasoline to 100% ethanol.
"there are even cars with 'flex-fuel'" is an understatement.
They were 90% of small car sales and 23% of total circulating vehicles as of 2008, probably more now.
For some odd reason the manufacturer of my lawn mower warns me not to use more than 10% Ethanol content fuel, or else my warranty is void. I'll assume it was to save about a dollar or two on gaskets and o-rings.
My lawnmower sat unused for about 4 years in a shed. Last year I tried to use it and gas leaked all around it. The ethanol left in the tank had eaten out all the little plastic pieces and seals in the ignition system.
Flex Fuel Vehicles are a thing in the United States too; but only up to 85% ethanol. One of my vehicles will run on E85, but since it would cost more and is not as available as regular gasoline, there is no real reason to use it.
It's cheap race gas at about 105 octane. I had my previous car tuned for it. The only problem is that it is very inconsistent at the pump. You don't always get e85. Some times it's e80 other times it's e75. The blend is also dependent on the weather. In cold weather states you only get about 3 months of true e85, in the winter the pump has a blend of e60. For a regular commuter car it's not a big deal and is necessary to ensure it starts properly in cold weather but when talking about cars that need a specific stoich ratio it's critical. Best way around it is to buy a barrel of it lol.
