Ethanol fuel treatment: everything you need to know

Why ethanol needs managing

Ethanol is hydrophilic: it draws water out of the air. When enough water gets into the tank the ethanol and water can separate from the petrol (phase separation), leaving a layer that will not burn properly and promotes rust. Ethanol can also degrade rubber and plastic fuel system parts over time. Engines that sit for long periods, such as mowers, generators, boats and seasonal vehicles, are the most exposed because the fuel has time to absorb moisture and go off.

The benefits of an ethanol fuel treatment

A good treatment does three things:

• Prevents fuel system corrosion by forming a protective barrier on metal surfaces such as injectors and carburettors
• Keeps the engine running cleanly by helping remove the carbon and varnish that build up over time
• Extends fuel life, so petrol that sits in the tank for weeks or months still starts and burns properly

How it works

A typical ethanol treatment combines detergents, stabilisers and corrosion inhibitors. The stabilisers slow the oxidation that makes fuel go stale; the detergents clean the injectors and valves; and the corrosion inhibitors coat the metal parts of the fuel system. Some products also bind small amounts of water so it passes through and burns during combustion rather than pooling in the tank.

Choosing the right treatment

Consider these before you buy:

• Engine type: small engines in lawn equipment have different needs from a car, and marine engines need a product rated for marine use
• Ethanol content: higher blends need a more robust treatment
• The label: look for a product that states compatibility with ethanol-blended fuel and check the dosage; more is not better and overdosing can cause problems of its own

How to use it

Dose, timing and handling:

• Always use the dose on the label; concentrations vary between products
• Add it right before filling up so it mixes with fresh fuel
• For equipment going into storage, treat the last tank of fuel and run the engine for a few minutes so treated fuel is in the whole system
• Use it in a well-ventilated area, wear gloves, keep it away from flames and heat, and store it sealed in its original container

Common myths

The first myth is that a treatment is unnecessary because ethanol blends are already formulated for engines. The fuel is fine to run, but it still absorbs moisture and still goes stale faster than straight petrol. The second is that only old vehicles are affected. Modern engines also suffer from phase separation and moisture when the fuel sits, and small engines of any age are the worst affected. The third is that treatments are a marketing gimmick: many mechanics recommend one as routine for anything that is not used every week.

Frequently asked questions

The questions the counter hears most:

• What happens if I skip it? Moisture in the fuel can cause separation and corrosion, and the resulting sludge clogs fuel lines and injectors, which means poor running and costly repairs.
• Can I use it in any engine? It is generally safe for most petrol engines, including cars, motorcycles and small engines such as mowers and generators. Check the owner's manual or ask if you are unsure.
• How often? Every fill if you regularly use ethanol-blended fuel, and always before putting equipment into storage.