What’s your Poison?

Is alcohol in petrol poisoning your car? Well, if your car was made before 2002 then from next year (2021) there is a good chance it will. 

Petrol, gasoline, dinosaur juice. Whatever you call it there’s no doubt it’s changed a lot over the last few decades.

Within the UK classic car enthusiasts have experienced the withdrawal of several fuels. First the lower octane 2-star petrol went, then 4-star. The final nail in the coffin for the old leaded fuels came with the withdrawal of LRP (lead replacement petrol, which contained a lead substitute).

Bio Fuels & Ethanol

Now there are creeping moves towards bio fuels. For unleaded petrol in the UK that means currently up to 5% of the fuel is ethanol. You’ll see an E5 label on the pump identifying it as such.

Unleaded fuel blended with ethanol produces less carbon dioxide when it’s burned. So it helps the government meet their carbon reduction targets. Sort of. It’s also less energy dense than the petrol it replaces, which means you need to burn more of it for the same power output. So, decreased miles per gallon. Try figuring that logic out.

What is Ethanol?

Ethanol is alcohol, the exact same stuff you find in your favourite pint or gin. It’s not good for you and it’s not good for your classic car. Your car won’t suddenly lose its inhibitions and become more sociable, but ethanol is highly volatile and corrosive.

Ethanol absorbs moisture from the air. One thing nobody wants is moisture in their fuel system.


When ESSO’s famous advert suggested putting a tiger in your tank I’m not sure they ever envisaged that petrol would have more in common with an Asian branded beer than an actual tiger.

Effects of Ethanol

Flexible fuel hoses are degraded (dissolved) by E10 unleaded. E10 is likely to cause for classic cars to suffer corroded carburettors, damaged fuel pumps and blocked fuel filters as well. Corrosion at the top of fuel tanks due to increased moisture levels in fuel is another possibility.

E5 premium unleaded is fine for most classic cars, though a lead replacement additive such as Classic (Castrol) Valvemaster may need to be added to protect against valve recession and engine knocking.

Products such as Castrol Valvemaster also contain chemicals to stabilise ethanol and mitigate its effects. It may not be suitable for your car if it’s a modern classic with a catalytic converter. Along with Millers they been endorsed by the Federation of British Historic Vehicle Clubs (FBHVC), so it’s definitely worth considering.

E10 Petrol by 2021

The UK government has committed to the introduction of unleaded containing 10% ethanol by 2021.

It’s already commonplace in continental Europe and the USA. So beware if filling up there. It’s also being introduced across China. So it is definitely coming.

This is likely to effect up to 600,000-700,000 vehicles registered prior to 2002, which are incompatible with E10 fuel. In fact some vehicles registered up to 2004 may be recommended by the manufacturer not to run on E10 without modification.

If you are unsure the RAC recommend checking with your vehicle manufacturer for compatibility with E10 fuel.

For a while anyway the government has pledged E5 fuel will remain on sale along side E10. However, this may only be in the form of super unleaded fuels, which are typically more expensive than their premium counterparts. And for how long, who knows?

How Do I Protect My Car?

It will be well worth paying the extra few pounds for a tank of E5 super unleaded fuel. At least until such time as it is no longer available. At that point an additive such as Castrol Valvemaster or Millers to help mitigate the effects of ethanol is surely very sensible indeed.

In the meantime it’s also worth considering replacing flexible fuel hoses with ones suitable for E10 fuel.

The only alternative would seem to be electrification of your classic, which for most of us would be like ripping the beating heart and soul out of our cherished vehicles.

Happy motoring.

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