September 2021: while most of the population was concerned with breaking their way out of a global pandemic, the UK quietly switched to E10 petrol as its default garage forecourt blend. Most motorists, or at least most of those with cars built after the turn of the millennium didn’t notice the change, but sporadic users of small engines – be they lawnmowers, chainsaws or outboard motors – started to encounter some issues straight away.
E10 petrol contains 10% ethanol, and you guessed it, E5 contains 5% ethanol. Ethanol is a form of alcohol, which like other forms of alcohol can be produced from crops and added to fossil fuels to reduce their carbon footprint. This is why governments worldwide have legislated for adding successively larger quantities of ethanol to forecourt gasoline to help meet climate targets. Fierce debates about the huge swathes of land this practice takes out of food production are not within the remit of a boating magazine.
Ethanol issues
What is within our remit is the reality that ethanol-blended petrol in small outboard motors presents or exacerbates several medium-and long-term reliability issues that were all much more manageable in older ethanol-free petrol.
Ethanol is hygroscopic.
As anyone who has enjoyed a ginlayers, one containing the (highly corrosive) water and ethanol mix, and floating on top of it a layer of reduced octane petrol, now depleted of its ethanol. Outboard engines will flatly refuse to run on either of these unpalatable fluids.
