E20 Fuel – What It Means for Your Car, and Why We’re Concerned

Over the past few years, most UK drivers have become familiar with E10 petrol. Introduced as the new standard unleaded, E10 contains up to 10% ethanol, compared to the old E5 blend (5% ethanol). On paper, it’s meant to reduce carbon emissions and cut reliance on fossil fuels.

But here in the workshop, we’ve seen the other side of the story.

The Reality of E10 in the Workshop

Since E10 became the norm, we’ve had countless issues with cars that simply don’t run properly on it. Some of the problems we’ve seen include:

• Rough running and hesitation under load

• Check engine lights triggered by lean mixture faults

• Premature fuel pump and injector wear

• Corrosion or perishing of fuel system components in older cars

One example close to home was our own VW Polo. A customer had topped it up with a small amount of E10 before returning it. Immediately, it developed multiple running issues - misfiring, hesitant acceleration, and poor idle. Once we drained it down and filled it with Shell V-Power (premium E5), the car ran perfectly again.

This isn’t an isolated case. Many of our customers have reported smoother running, better MPG, and fewer problems since switching back to premium fuels like Shell V-Power or BP Ultimate.

What Happens When We Move to E20?

Now, talk is growing about E20 petrol - a fuel with 20% ethanol content. Other countries such as Brazil already use high-ethanol fuels, but their cars are designed as flex-fuel vehicles, built to cope with the differences in combustion and chemical properties.

Most cars in the UK simply aren’t designed for this. If E10 has already caused:

• 2–3% lower MPG,

• engine hesitation, and

• fuel system wear,

then E20 could realistically double those issues. We could be looking at 4–6% worse MPG, more frequent fuel-related breakdowns, and accelerated wear on injectors, pumps, and seals.

Why Ethanol Causes Problems

• Ethanol absorbs water - leading to corrosion inside fuel systems.

• Lower energy content - less mileage per litre compared to petrol.

• Different combustion properties – some cars run leaner and hotter, which stresses valves, injectors, and catalytic converters.

• Not kind to rubber or aluminium – seals and components wear faster.

Unless your car is specifically designed as an ethanol “flex-fuel” model, it will never be truly happy on high ethanol blends.

Can Remapping Help?

One of the ways to optimise a car’s performance and efficiency when fuel quality changes is through engine remapping. While remapping won’t change the chemical properties of ethanol, it can adjust how your engine delivers fuel and power to better cope with different blends.

At Hurn Performance, we’ve seen excellent results remapping cars to get:

• Smoother power delivery

• Better throttle response

• Improved MPG (especially when using premium fuels)

So while E20 may cause more widespread issues, remapping could help certain vehicles adapt better and run more efficiently - provided the base fuel is still of good quality.

Our Advice

For now, our experience is simple:

• If you’re running E10 and notice poor performance or economy, try a tank of premium (E5) petrol like Shell V-Power. Many customers see an immediate improvement.

• For older vehicles, premium fuel isn’t just a luxury - it’s a way to protect your engine and fuel system.

• Keep an eye on future announcements about E20. If it does become the new standard, we expect the problems we’ve seen with E10 to get significantly worse.

• Consider remapping as a long-term solution to get the very best out of your engine – especially if you’re committed to using premium fuel.

Final Thoughts

We’re all for cleaner fuels and reduced emissions - but the reality is, not all cars are ready for E10, let alone E20. Until the vehicle fleet is designed to handle higher ethanol blends, the best way to protect your engine is to stick with premium petrol where possible and explore remapping options to optimise performance.

We’ll continue to monitor how fuel changes affect the cars coming through our doors, and we’ll share what we learn so our customers can keep their vehicles running at their best.