E10 Petrol Problems: Is Your Car Struggling?

E10 is a genuine mechanical risk for older fuel systems, and the only pump fix is premium "super" petrol, which still uses the E5 blend. That protection costs a measured 17.3p a litre more than standard. For a classic doing low miles it is cheaper than it sounds - £8.65 extra on a 50-litre tank, and a 2,000-mile-a-year car only uses three or four of those.

• E10's ethanol degrades older rubber, plastic and fibreglass fuel components.
• Standing E10 absorbs water and separates - a storage problem, not a driving one.
• Super petrol (97+) is the widely available E5; the premium costs 17.3p a litre.
• Low annual mileage keeps the E5 bill in tens of pounds a year, not hundreds.

The ethanol shift

In September 2021, the UK switched standard 95-octane petrol from an E5 blend to E10, meaning standard petrol now contains up to 10% renewable ethanol. The change reduced fleet-wide CO2, but it introduced real mechanical questions for drivers of older vehicles - and quietly moved E5 behind the premium price label.

Why ethanol is bad for old cars

Ethanol has two properties that make it hostile to older engines:

• It is a solvent. Ethanol aggressively attacks older rubber fuel lines, plastic seals and fibreglass fuel tanks. Over time these components become brittle and crack, leading to fuel leaks you do not want anywhere near a hot engine bay.
• It is hygroscopic. Ethanol absorbs moisture from the air. If E10 sits in a tank for weeks without use, the water and ethanol separate from the petrol and sink, causing internal rusting and misfires.

Is my car safe?

If your car was built after 2011, it is compatible with E10. If it was built between 2001 and 2011, it is very likely to be safe, but you should check the government's official E10 compatibility checker before assuming. Anything older needs to be treated as incompatible until proven otherwise - and "runs fine on E10" is not proof, because the damage is cumulative.

What the E5 premium actually costs a classic

Most advice stops at "premium fuel is expensive". We measure the gap: at every forecourt publishing both standard and super petrol, the premium averages 17.3p a litre. What that means annually depends entirely on how far you actually drive the car:

For the low-mileage cars that actually need E5, the protection costs tens of pounds a year - cheaper than one replaced fuel line. The economics only turn against E5 for high-mileage daily drivers, and those cars are mostly newer and E10-compatible anyway. The octane question for modern cars is separate; our E10 versus E5 guide covers it.

Storage matters as much as the pump

The hygroscopic problem is about standing fuel, not driving. For a car that sits over winter: fill the tank full to leave less air space for condensation, use a fuel stabiliser designed for ethanol blends, and start it up every few weeks for a proper run rather than a few minutes of idling. A tank of fresh E5 plus a stabiliser and a full tank will overwinter far better than a half-tank of E10. Our fuel additives guide looks at what the bottles do and do not do.

Finding E5 near you

Super petrol is stocked at most oil-major forecourts and many supermarkets, but not everywhere, and prices vary widely - the gap between the cheapest and dearest super petrol in one town is often wider than the E10 spread. If you must avoid E10, use FindPetrol to find the stations near you selling the cheapest E5 before you set off, rather than paying whatever the nearest forecourt asks. Availability differs by area; see our hyper-local pricing guide for how widely prices diverge within a single town.

Comparing petrol prices before you fill up

Whichever grade you choose, the forecourt matters more than the badge. Standard petrol currently runs from well under to well over the 161.2p national average depending on where you stop. Check petrol prices near me by postcode, or see the full picture on our UK fuel prices page before you commit to a tank.

Frequently asked questions

Will one tank of E10 damage my classic?

A single accidental tank is very unlikely to cause harm. The damage mechanisms - seal degradation and water absorption - act over months and years of exposure. Drain it if you want peace of mind, but do not panic.

Can I mix E5 and E10?

Physically, yes - the blends mix and the result is somewhere between the two. But for a car that must avoid ethanol, mixing defeats the point of buying E5. For compatible cars, mixing is completely fine.

Is super petrol always E5?

At most UK forecourts, yes - 97+ octane super petrol is the E5 blend. A small number of premium products are now E10-based, so check the label on the pump if your car is strictly ethanol-sensitive.

Figures updated 27 September 2026. The E5 price premium is the average difference between each station's own standard and super petrol price, across the 6,229 UK forecourts publishing both via the CMA-mandated fuel price scheme. Annual costs assume 30mpg, typical for older petrol engines. Compatibility guidance follows the government E10 checker. Averages move daily; live prices are on our UK fuel prices page.