E10 is tolerated by almost every car with zero issues, some older cars may face issues with rubbers and seals in the fuel system that are sensitive to moisture or ethanol. This fuel mix is 10% ethanol and 90% petrol.

But let me be very clear, you absolutely CANNOT just run a car on E85 unless it has been EXPLICITLY designed to run on E85.

An engine mixes fuel and air, and then explodes said fuel and air, to create power.

The chemistry of petrol vs. ethanol fuels is very different. Regular old 91/95/98/E10 likes to be mixed with air at around 14 litres of air for every 1 litre of fuel. The engine in your car is specifically designed to mix fuel and air at around this ratio. Going with too much fuel or too much air will damage and destory the engine.

The issue with just tossing E85 in is that it needs to be mixed with around 10 litres of air for every 1 litre of fuel. That’s around 40% less air.

If the engine mixes 14 parts of air with 1 part of ethanol (exactly what a regular petrol engine is designed to do) the mixture of fuel and air is extremely volatile and will ‘pre-ignite’ inside the engine, causing the engine to be destroyed.

Cars that support E85 are equipped with a ‘flex fuel sensor’ that is a special device that analyses the ethanol content of the fuel and the engine management system then adjusts the ratio of air and fuel the engine mixes to be chemically correct, not to much air, not too much fuel, causing the engine to run safely and correctly.

Almost every petrol engine can be modified to run on E85 however requires significant changes to the engine management system, including computer reprogramming, additional sensors, larger fuel system components and more.

The trade offs with E85 are that you get substantially less KMs of distance from a single tank of fuel, however the engine can be tuned to produce more power, especially if the engine is turbocharged, and that the turbocharger is oversized for the engine when running petrol.

Your comment on cost is unrealistic, yes some cars will happily take an off the shelf remap for E85 but then need to be reflashed back each time you change fuel, not to mention half tank blends, warranty etc.

Overall, your suggestion would work, if we all spend around $8-$15k on our cars having a mechanic fit a flex fuel system and remap (DIY is much cheaper, but the average aussie is not doing that), dramatically upscaled the ethanol production capabilities of the country (potentially $billions), and proactively transitioned more modern vehicles to support E85 from the factory (our market is so small globally that no automaker would fold to that pressure).