What Petrol Should You Use for a Lawn Mower in the UK?

What Petrol for a Lawn Mower UK

Using the correct petrol in your lawn mower is essential for keeping the engine running smoothly and preventing long-term damage. Since fuel standards changed in the UK, many gardeners have been unsure about which type of petrol is safe, especially with the introduction of E10 at petrol stations. Choosing the wrong fuel can lead to performance problems, engine wear and costly repairs. This guide covers exactly what petrol to use in your lawn mower and how to store it correctly.

Use Unleaded Petrol with No More Than 10% Ethanol

Most modern petrol lawn mowers in the UK are designed to run on regular unleaded petrol, typically labelled as E10 at the pump. E10 contains up to 10% ethanol, which is acceptable for many mowers with four-stroke engines. However, ethanol can attract moisture and degrade over time, which may affect mower performance if the fuel is stored in the tank for too long.

If your mower's manufacturer recommends a lower ethanol content, you may be better using E5 petrol (premium unleaded), which contains a maximum of 5% ethanol. This fuel is often labelled as super unleaded and is more stable for engines that are sensitive to ethanol or used less frequently.

Check Your Lawn Mower’s Engine Type

Before filling up, it’s important to know whether your mower has a two-stroke or four-stroke engine. Most petrol lawn mowers in the UK today use four-stroke engines, which take straight unleaded petrol and have a separate oil reservoir. Two-stroke engines, which are less common, require you to mix oil with the petrol before filling the tank. Using straight petrol in a two-stroke mower will cause immediate damage.

Always refer to your mower’s manual to confirm the engine type and recommended fuel specification. If the manual calls for a specific ratio of petrol to oil for a two-stroke model, follow it carefully.

Avoid Old or Stale Petrol

Petrol degrades over time, especially when exposed to air and temperature changes. If petrol is left in your mower’s tank or fuel can for more than 30 days, it can start to go stale. This leads to hard starting, poor performance and a risk of clogging the carburettor. For the best results, only buy as much fuel as you need for a few weeks at a time, and store it in a properly sealed, labelled container.

At the end of the mowing season, it’s a good idea to drain the tank or run the mower dry to prevent stale fuel sitting in the engine over winter.

Consider Using Fuel Stabiliser

If you need to store petrol for longer periods, particularly over winter, adding a fuel stabiliser can help preserve the petrol and reduce the risk of engine issues. These additives slow the breakdown of the fuel and help protect internal components from corrosion, especially if ethanol content is a concern.

Stabilisers are available from most garden machinery suppliers and are a good investment for petrol mowers that are used infrequently or stored for months between uses.

Final Word

In the UK, most petrol lawn mowers are compatible with regular E10 unleaded petrolbut only if it’s fresh and used within a few weeks. For older machines, two-stroke engines or mowers used less often, using E5 premium fuel may offer better reliability and protection. Always check your mower’s manual before filling up, and never leave old petrol in the tank between seasons. With the right fuel and a bit of care, your mower will run cleaner, start easier and last longer.