Why my M5 drinks a lot

Although the ethanol content in fuel is diluted to 10%, I’d still be wary of using it long term in the engine of a classic car like the E30 M3’s S14, E9’s M30 and the E28 M5 and E24 M635 CSi’s M88/3

Ethanol has a lower energy density, it is bad for some plastics and rubbers and it absorbs water. The latter means it can corrode bare metal and eat away at fuel lines. However, at 10% dilution with petrol, the corrosive effects are only just noticeable, and this, perhaps, is why the 10% level was chosen.

There is a lot of scientific research behind this, which I reference and you can check it out online, see below. The key thing you should do is read the Owner’s Handbook that came with your car. I dug mine out (there have been a few other purchases since 1988) and it said no more than 3% methanol. The car was probably fine before, as petrol was “up to” 5% ethanol, but with the change to E10, I was concerned. So, I did my research and decided in October to switch some of my cars to Esso Supreme (at 147.9p/L) as it is 0% ethanol in my part of the UK. See www.esso.co.uk/en-gb/fuels/petrol for more information.

The other car on the road, my E66 760Li with BMW’s finest (when it left the factory, at least) N73 V12 can take E10 fuel. In fact, the manual says its sensors can cope with 91-100RON or higher. Great! It is getting supermarket regular from wherever is cheapest, because when I tanked up with Sainsbury’s regular yesterday it was 145.9p/L. As I type this, Esso Supreme shot from 168.9p/L to 178.9p/L and who knows where the price is going. The PetrolPrices website has been invaluable, but the app crashes occasionally from high demand.

Further research on ethanol in fuel to write this article unearthed from www.iopscience.iop.org/ article/10.1088/1748-9326/ac2e35/ meta and www.pnas.org/doi/10.1073/ pnas.2101084119, which basically lay bare the true environmental cost of bioethanol in the US. These investigations reveal that 10% ethanol in fuel does not produce the desired 20% reduction in CO2, it actually increases CO2 by 24%. Yes, yes, crops take CO2 from the air and when cars burn it, crops can use it over again. However, the change of land-use to corn means an increase in ploughing, more fertilisers and that releases vast quantities of CO2. It also increases crop prices by 20-30%. Funny that. So, this research shows that the original decision to go for bioethanol was not clearly thought through. A 20% reduction in CO2 sounded great, but at 10% dilution the reality is only a 2% reduction on paper after 28 years. As they got it wrong, the world suffered the land-use CO2 penalty and won’t benefit at all. The US Renewable Fuel Standard (RFS) is up for review and maybe this time they’ll get it right. Although, when you see the next great idea from politicians, ask how many of them have an engineering or science degree, or did a lobbyist make up their mind at a business meeting.

Meanwhile, the E61 M5 has also gone on the wagon. Its tank is full with Esso Supreme because it is 99RON and has a higher energy content. For many years I believed the much repeated hype surrounding Shell VPower, but now that has 5% ethanol while in much of the UK Esso 99 doesn’t. Your mileage, performance and belief systems may vary.

Words – Robert Walton Sharp Photos – Jeff Heywood/BMW Press

Following the introduction of E10 petrol in September 2021, plus a few articles and comments in Straight Six, it is possible that some readers, contributors and, sadly, politicians, are still confused about the pros and cons of ethanol in fuel.

Robert’s stunning Monaco Blue E61 M5 has also been switched over to Esso Supreme 99RON, which contains no ethanol in much of the UK

The Heywood’s M850i runs much smoother and is definitely more economical running on Esso’s Supreme 99RON petrol…

I must admit our G15 M850i has run much cleaner/smoother on Shell Synergy Supreme 99RON since I switched over last September and on a long run, the fuel economy savings have been quite noticeable. - Ed