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Posted by on Apr 18, 2011 in Boat Maintenance, Engines, Fuel, Outboard Engines, UK, US |

Ethanol and Water In Fuel

Now that we're all using ethanol-based fuel, how can we tell if there's water in it?

Question: I’ve read in a number of places that ethanol increases the risk of water settling into my fuel. How can I tell if this has happened?


Most outboard engines have a small inline filter that will show if water is in the fuel.

Answer: Aside from very erratic engine performance (and maybe even a no start condition in the extreme), one of the best ways to tell if you have water in your fuel is with a visual check. This of course dictates that you have a clear fuel bowl on your fuel/water separating filter. Incidentally, if you do not have such a filter installed on your gasoline-fueled engine, whether inboard or outboard, you are just asking for trouble! Standard issue metal spin-on fuel/water separating filters don’t help here. Not that they don’t work—it’s just that you can’t see what’s going on inside them.moeller-filter

I’m using Moeller clear bowl units on my boats right now and they really work well. Most outboard engines today will have a small inline separating filter under the cowl that can provide a visual clue as well. In any case water will always settle to the bottom of the filter bowl and it will be relatively clear compared to the fuel so it’s really easy to spot. And most fuel/water separating filter set-ups will have a valve at the bottom of the bowl to facilitate draining of the water from the filter.

—Ed Sherman