I am curious, is that a surprising result to you? Genuine question. I know the “E10 ruined my fuel economy” crowd is reasonably strong around here.
Just as a general PSA: if you compare three petrol types (“pure”, E5 and E10), you’ll notice rather quickly that there’s no noticeable difference between them. If we take pure petrol as the yardstick at 100% energy density, then E5 is 98.3%, and E10 is 96.7%. In other words, if you run a 100% accurate test between “pure” petrol and E10 (the worse of the two ethanol fuels), you’ll notice a 3.3% difference. Meaning that if pure petrol does exactly 50mpg, E10 will do 49.3mpg, E5 will do 49.64mpg.
And that’s all there is to it. People argue back and forth, you just need to look at the energy density. Yes, E10 carries marginally less energy per litre, but people here were suggesting they lost 10, 15, sometimes even 20% of their economy by switching fuels (usually more than they’d lose switching to even E85).
Now. As for using E5 vs E10, honestly.. The differences are so marginal, just go with whatever makes the car go broom. The vast majority of people will not notice a difference of any kind, be it the tiniest increase in fuel consumption on E10, the tiniest amount of fossil fuels avoided with E10, the tiniest amount of better lubrication on E5, etc.
The one thing that can (but won’t) make a difference is the knock resistance. For the vast majority of people here 95RON (E10) will do just fine – in higher performing engines, E5 (97RON) or higher (“premium fuels” like V-Power, Momentum etc – all the 99RON stuff) might lead to a small increase in power/efficiency. I don’t think there’s any high compression engines on the scheme though, hence won’t make a difference.
That all said, we only refuel once every 8-12 weeks, so we splurge on the “good stuff” (Momentum, usually) – despite almost certainly just being a “feel-good” choice. Makes me feel better, and we love the car so might as well. Kezo certainly is correct though, assuming you don’t need high octane fuel, the premium for E5 completely negates the theoretical “range advantage” (swings way the other way in fact) over E10. As a general rule of thumb, if your car can run 400 miles per refuel, then switching from E10 to E5 grants you around an extra 7ish miles of range. Now consider that E5 is what, 5-10p dearer than E10, over an entire fuel tank – lets say 35l – you pay £2-£4 extra for E5/7 miles extra. You’ll always get way more by getting £2-£4 extra of E10 (numbers not accurate, but ballparks).
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.