Both E5 and E10 petrol refer to the ethanol content in the fuel. Ethanol is a renewable fuel derived from plants, which helps reduce greenhouse gas emissions. However, ethanol can be more corrosive than pure petrol, which is why the fuel type matters.

E5 Petrol: Contains up to 5% ethanol and is often labeled as “premium” or “super unleaded” in the UK.

E10 Petrol: Contains up to 10% ethanol, making it a slightly greener choice. E10 became the standard grade in the UK as of September 2021.

Today we are only going to be talking about petrol in the UK and this will likely differ between countries however it is worth noting if you are anywhere in Europe as this will also apply to most European countries.

While E10 may be better for the environment, its higher ethanol content can affect cars that aren’t designed to handle it.

Benefits and Drawbacks of E5 Petrol

Benefits:

• Compatible with Older Engines: E5 petrol is generally safer for older vehicles and classics, as these engines were designed long before ethanol became common.
• Better for Fuel Systems: Ethanol can corrode rubber seals, plastic components, and even metal parts over time, especially in cars built before 2002. E5’s lower ethanol content minimizes this risk.
• Improved Fuel Efficiency: E5 petrol tends to offer slightly better fuel economy, as ethanol has less energy than pure petrol.

Drawbacks:

• More Expensive: E5 is often priced higher at the pump, which can add up over time.
• Lower Availability: Since E10 is the new standard, E5 may be harder to find in some areas, particularly outside of premium brands.

Benefits and Drawbacks of E10 Petrol

Benefits:

• Eco-Friendly: With its higher ethanol content, E10 is more environmentally friendly, helping reduce CO2 emissions.
• Widely Available: E10 is now the standard across the UK, making it easy to find and generally cheaper than E5.

Drawbacks:

• Potential Engine Issues in Older Cars: For vehicles not designed to handle higher ethanol levels, E10 can cause engine damage or wear over time.
• Lower Fuel Efficiency: Ethanol has a lower energy density than petrol, so you might see a slight drop in miles per gallon.
• Increased Wear on Components: Rubber seals, plastic parts, and even metal in fuel systems are more likely to degrade with prolonged E10 use, especially in cars that aren’t E10-compliant.

Why Using the Right Fuel Matters: E5 for Non-E10-Ready Cars

If your car isn’t E10-compatible, using E10 could lead to various issues. Ethanol absorbs water, which can lead to condensation in the fuel tank, causing rust in metal components and corrosion in other parts. Over time, this can lead to misfires, engine hesitation, and reduced fuel system lifespan. That’s why it’s crucial for older vehicles, like classic cars or pre-2002 models, to stick with E5.

The Mazda 323F and E10 Compatibility

The Mazda 323F (1994), equipped with a 1.6L petrol engine, is a great example of why fuel choice matters for older vehicles. Like many cars from the early ‘90s, this Mazda was not designed with ethanol-rich fuels in mind. The rubber seals, hoses, and metal components in its fuel system can wear faster when exposed to E10. This leads to a higher risk of leaks, fuel pump failure, or clogged fuel lines, potentially causing serious engine issues if E10 is used regularly.

My Experience with E10 in My 1994 Mazda 323F

I learned this lesson firsthand with my own 1994 Mazda 323F. I filled up with a full tank of E10 petrol from ASDA. Initially, it ran fine, and I didn’t notice anything unusual. However, after about 50 miles, I started to feel a distinct hesitation in acceleration. The car felt sluggish, and it was clear it wasn’t happy with the E10 fuel.

To resolve the issue, I decided to empty the tank on a long motorway run and then refilled it with E5 from Shell. Within a few miles, the difference was obvious—the engine ran smoothly, and the hesitation disappeared. The experience highlighted just how sensitive older engines can be to fuel type.

Key Takeaways: Why You Should Choose the Right Fuel for Your Car

1. Check Compatibility: If you drive a car made before 2002, it’s best to use E5. Many cars built after 2011 are designed for E10, but it’s always good to confirm.
2. Consider Long-Term Effects: Even if your car seems to handle E10, it may still cause long-term damage to the fuel system, especially with repeated use.
3. Pay Attention to Performance: If you notice reduced performance, engine hesitation, or rough idling after switching to E10, it’s a sign your car may not handle it well. Switching back to E5 could improve performance and protect your engine.
4. Storage Matters: E10 is not ideal for cars that aren’t driven frequently, as ethanol can absorb moisture over time. If you store your car over winter, it’s best to keep E5 in the tank to reduce the risk of corrosion.

E5 or E10? The Choice is Clear for Older Cars

Choosing between E5 and E10 petrol might seem like a small decision, but it can have big implications for your car’s health, especially if it’s an older model like the Mazda 323F. For classic car owners and those with vehicles not designed for higher ethanol content, E5 offers peace of mind and better engine compatibility. For those driving newer, E10-compatible cars, E10 remains a more eco-friendly and cost-effective choice.

If you’re ever in doubt, remember my story—while the Mazda 323F survived its tank of E10, it was a clear reminder that some classics are best left with the fuel they were designed to run on.