How to maintain your fuel system


Whilst there are many aspects that need to be considered when maintaining your garden machinery, fuel is one of the most important, but at the same time is often over looked.

Changes to government regulations mean that the petrol we buy from the pump today is different to the petrol we have been used to in the past. The result of these new regulations is a compound of over 100 chemicals that work well in your car, but without proper understanding can cause various issues with the smaller engines used in garden machinery. The main concern is the increased use of Ethanol in petrol.

In this example of phase separation you can see the clear layer of Ethanol/Water sitting below the petrol.

Ethanol is added to petrol as mandated by the EPA to lower carbon emissions. As a result, over time, the Ethanol blended fuels suffer with phase separation. Ethanol is hydroscopic, so it absorbs moisture from the air then separates from the petrol by dropping to the bottom of the tank. This is because when the Ethanol reaches saturation point it becomes heavier than petrol. Once separated, there is no turning back and the petrol will need to be thrown away.

The problems that can occur

There are several issues that can be caused by running your machine on stale/separated fuel. If the engine is running and suddenly draws water you can have damage from thermal shock or hydro-lock. If the engine draws the Ethanol/water mixture or just Ethanol you can have problems where it will operate in an extremely lean condition, which can cause significant damage or even complete engine failure. If the engine draws the remaining petrol, it will operate very poorly due to the lower octane that is a result of no longer having Ethanol in the fuel.

Another issue caused by the absorption of water by Ethanol is the exposure of the parts inside your engine and carburettor to moisture resulting in a build up of corrosion within these components. Over time this build up of corrosion will gradually reduce the size of the fuel lines/pipes and reduce the amount of fuel that can get to your engine, resulting in a lack of power. This is especially true with small engines as many still use aluminium parts that corrode more quickly resulting in oxides that look like white powder.

Finally, Ethanol is very good at loosening debris that normally builds up in the fuel tank, which may seem to be a benefit but these lumps can cause blockages at various points throughout the fuel system.

What you need to do

What most people don’t know is that the “shelf life” of petrol from your local filling station is approximately 4 weeks, as that is when the fuel begins to degrade to a point that it can cause issues with your garden machinery. When petrol is mixed with 2-Stroke oil this degrading can appear to be accelerated because of the separation that occurs between petrol and 2-Stroke oils regardless of the Ethanol content. 2-Stroke oil will separate from the fuel over time and sit at the bottom of the fuel tank. The 2-Stroke oil can be re-mixed, assuming you have checked for phase separation first.

Some people drain their fuel tank and run the engine until it runs out of fuel. This can cause varnishing issues in your carburettor where the remaining fuel residue dries onto the internal components. An example of this can been seen above.

If your garden machinery is left for any period of time then you will need to do something to prolong the life of your fuel. There are various fuel stabilisers available to help with this and even some 2-Stroke oils that include stabilisers. For the occasional user, a good option is to switch to an Alkylate petrol like Aspen Fuel.

Your Options:

  • 1. Switch to Aspen Alkylate Petrol (lasts up to 5 years)
  • 2. Use Fuel Stabilisers (lasts up to 2 years)
  • 3. Use 2-Stroke oil with built in stabiliser (2-Stroke only, lasts up to 3 months)
  • 4. Refresh your petrol monthly regardless of use

Aspen fuel has a shelf life of 5 years and is available as a pre-mixed 50:1 2-Stroke as well as a 4-Stroke fuel. It eliminates any concerns that are caused by modern fuels; it is cleaner for your engines, for the environment and for yourself.

Aspen Fuel will work out to be a more expensive option if you’re using your machinery regularly but you will find that the engine requires less maintenance as a result. Alternatively, fuel stabilisers can be purchased to prolong the life of Ethanol blended fuels. It is important to follow the instructions specific to the fuel stabiliser that you buy. Fuel stabilisers typically make the petrol last between 1 and 2 years.

To compliment this option, and a handy tip for 2-Stroke machines; Stihl’s range of two stroke oils, HP, HP Super and HP Ultra, all have fuel stabilisers built in, and will help your 2-Stroke mixed fuel last up to 3 months.

Finally, the other option is to replace the fuel that you store on a monthly basis. The old fuel will be good enough to use in the equivalent car and as we tend to fill our cars up quite regularly this can be quite an effective way to maintain the fuel you use. It is recommended that by using this method you mix the 2-Stroke oil with the amount of fuel you require for the job at the time.


Petrol issues have become more of a problem since the increased use of Ethanol in fuel. Small engines that are used occasionally are the most likely to suffer due to the nature of the problems that can occur. It is important that maintenance of the fuel system is not overlooked and the correct solution for you will depend on how you use your garden machinery.

The majority of starting issues that we see in our workshop have been caused by lack of maintenance with the fuel system and we often find that our customers are unaware how the changes in our fuels require a change in the way we use them. Maintaining your fuel and fuel system will likely save you money in the long term.