When my local petrol station has run out of E10 / 95 octane I’ve I used E5 / 97/98 octane but I can’t say I’ve noticed much difference in the running of my day to day cars. Never checked the MPG though as normally my trips are too varied to get a meaningful result.
Ethanol contains less energy than straight petrol therefore it follows that E5 contains more energy than E10 so in theory at least it’s likely to give you slightly better MPG because of that. Probably better than the government figures suggest because their figures could be slanted to encourage you to use E10
You will also have a higher octane fuel with E5 but that bit will be wasted unless you have a high performance engine, however I cannot see any harm would be done other than to your pocket.
Ethanol eats fuel lines on older cars, absorbs water and can cause problems if a car is left unused for long periods so E5 or E0
is a must for any classic car pre 2000 ish
