E10 Petrol    The Issues & Storage   

  All modern engines are warranted by the engine manufacturer to run on petrol with UP TO 10% ethanol content.

 In fact the UK is behind many countries in switching to e10. The US & many European countries have been running e10 for a number of years now.

 The simple advise in essence is the exact same as before.

 1 - If possible, use your fuel within 30 days of purchase.

 2 - if you can’t use your fuel within 30 days, you need to use a fuel stabiliser. The fuel stabiliser must be added within the 30 day window. It will not fix bad fuel.

 3 - MAKE SURE you use fuel stabiliser before any storage longer than 30 days especially over winter. Either leave the fuel system completely dry or full to the brim. Not half full. But the key is fuel stabiliser.

Or Simply Use 


              Stihl Motomix                 or                Aspen 4

 Now for the in depth explanation 

Stop reading now if you just wanted a simple answer!

 The biggest issue surrounding e10 we are likely to see more issues with is, water in fuel systems. Ethanol is HYGROSCOPIC meaning that it will absorb water molecules from its immediate environment. 

 E10 has the ability to hold 0.5% water in suspension without separating. That means that if we take 1000ml of e10 (900ml petrol, 100 ml ethanol) and we add 5ml of water, then the ethanol will hold the water molecules in suspension and carry the whole mixture through the carb and combustion process as 1. This is not going to cause an issue.

 The problem comes when the fuel is contaminated with more than 0.5% water. When this happens “phase separation” occurs and you get a water-ethanol cocktail at the bottom of the fuel tank/carb and straight petrol floating on top. Note that ethanol is partially used as an octane booster. So, the straight petrol that is left will have a reduced octane rating and could lead to severe engine damage through premature ignition. Commonly referred to as “knock” or “pinking”.

 It is a common misconception that ethanol sucks the moisture from the air. It doesn’t. It does however have the ability to absorb water molecules when it comes into contact with them. So where does the water contamination come from in the first place?? 

 Well it could be something as simple as pressure washing a machine off. But by far, the most common way that water contaminates a fuel system in storage is through condensation. When a half full vented fuel tank is stored it goes up and down in pressure with temperature changes. That’s 1 reason they are vented, to regulate pressure safely. However, to regulate the pressure the tank breathes. It basically breathes out cool dry air as the temperature rises and breathes in moist warm air usually in the evening as the temperature drops. Overnight the warm moist air in the fuel tank cools more and condenses, leaving water droplets on the inside walls of the fuel tank. These droplets are absorbed by the ethanol in the fuel and in the morning the cool dry air is pushed out again as the pressure builds again.

Having a half full, vented fuel tank in storage in a damp, cold shed over winter is the perfect storm for this to happen.

 If the tank is empty the tank doesn’t breath as much and there is no ethanol to absorb the water molecules. If the tank is full, there is less physical space for moist air to enter and condense so it makes it easier to keep the water contamination below that all important 0.5%. 

 Just to note, the fuel stabiliser will not stop the water contamination, it just means you can store a full tank of fuel without it going stale as quickly.

 Shire Garden Machines Ltd

01380 721575


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