I should also say I've always run Monty on E10, and it's important to understand E10 has a lower calorific value by volume than E5, so there is potential scope to improve my 37.2 simply by switching to E5. However, we need to separate fuel consumption, which is how much fuel the engine consumes over a fixed distance, from fuel economy, which is how much it costs to cover that same fixed distance.
E5, or what is being marketed at the pump these days as 'Super Unleaded', is of course more expensive to buy, so the real question we should be asking ourselves is....
Is running E5 'Super Unleaded' really worth it
In terms of ethanol content the new 'Super Unleaded' (E5) is actually more or less identical to the old 'Regular' we used to get at the pumps before September 2021, however, it does retain the higher 98 Ron octane level of the old 'Super Unleaded'. Make no mistake, this means even the new 'Super Unleaded' has a lower calorific value than the 'Super Unleaded' we were buying just two years ago. So, even if you've always run 'Super Unleaded', your fuel consumption will have increased in the last two years, and you can do nothing about that!
When E10 became the standard grade of petrol in September 2021 the AA said that fuel consumption would rise by about 1.6%, the UK government agreed with the AA when they quoted a 1-2% increase. We must consider this before we get sucked into all the millions oil companies invest in trying to encourage us to pay the 2-3% premium they typically charge for their so-called 'Super Unleaded'.
Also keep in mind that you will only see an additional benefit from the slightly higher octane level of 'Super Unleaded' if you or your ECU can advance your ignition timing to make use of it's greater resistance to knock (detonation), and even then you'll only really see a tiny power benefit under acceleration/load. E10 is still 95 Ron whereas E5 is typically 98 Ron, but in terms of consumption you'll be lucky to achieve any more than a 0.5% reduction in how much fuel the engine consumes from the slightly higher octane element.
Clearly paying a 2.5% premium or more for 'Super Unleaded', that at the very best will actually only deliver a 2% improvement in fuel consumption is a false economy, so if your car can accept E10 there's seldom any logical reason (other than a feel good factor) why you should ever choose 'Super Unleaded' over the cheaper E10 fuel.
However, if you run an older car that can only accept E5, you must pay the premium and use 'Super Unleaded'!
In summary, just like ULEZ, the move to E10 is actually another Tax on the poor who can't afford to buy a newer E10 compatible vehicle, the environmental sales pitch from the Government is really just a classic smoke screen (no pun intended). Just like ULEZ and air quality, the evidence presented to try and persuade us that E10 helps to meaningfully reduce carbon emissions is very weak indeed. When you study the facts, it's far more likely what we are actually seeing here is a Government strategy to stimulate new car sales. This is good for the economy, Tax revenue and the rich who invest in car production to enjoy dividends from the industry, but bad for the environment because it takes a massive amount of carbon to build a new car, especially an EV.
What we should be doing is encouraging people to keep their older cars longer, because while the older car will have higher tailpipe emissions the additional carbon it produces is still massively lower than the carbon it takes to build a whole new car to replace it. Instead of spending tens of millions on ULEZ cameras and pushing low energy ethanol on us, the money should go towards grants that pay for retro-fit modern engine management systems and high efficiency catalytic converters on older vehicles.
Such a strategy would support current thinking that says to repair and improve what you already have is a way more environmentally sound approach than making something new to replace it, only to throw what you already had that was actually perfectly serviceable into landfill.
