Water In Your Marine Fuel Tank: How to Tell

Ethanol problems combined with normal condensation -- and sometimes a bad load of fuel -- mean that your boat needs good water separators in place.

29th April 2013.
By Ed Sherman

Question: I’ve been told that besides issues related to ethanol in my fuel, excess water accumulation is probably one of the most common problems with marine engines today. Is there any easy way to check for water in my outboard engine’s fuel system?

fuel-water separator

This engine-side water separator is your last line of defense before water gets into your engine. Keep an eye on it, and empty out any water that accumulates in the bottom.

Answer: Besides your engine not running or running poorly, a periodic visual check of the fuel water separator on you engine is the best way to see if water is beginning to accumulate in your fuel system. Most modern engines have them installed, and some of the more sophisticated units even have wired electrodes that will sound an alarm when water gets to a certain level in the canister. In the photo above, anything you see below the red line shown is water, which will always settle to the bottom of the canister. Keep in mind that this small fuel strainer is the last line of defense in your fuel system. You really need a paper element fuel-water separator further upstream (closer to your fuel tank) in your system. I also recommend keeping a spare filter canister on board in case you accidentally pick up a mega-dose of water when refueling somewhere.

racor fuel filter

Replaceable filter canisters are effective, but it’s impossible to see inside them.

The trouble with the paper element fuel water separators (see inset photo) is that although they do a great job of filtering out debris and separating water, they are opaque for the most part so you can’t see what’s happening inside them.  (OEM units are typically opaque; after-market units often have a clear fuel bowl at the base so you can see any water contamination.)

The bottom line here is that you need to get any excess water that builds up in your fuel system out of the system ASAP.

Also keep in mind that the occasional small amount of water that settles to the bottom of the canister on your engine is no cause for alarm. All fuel has some small amount of water in it that’s caused by condensation settling in the fuel storage tanks that are part of the fuel distribution chain. With the separator shown in the top photo, simply unscrew the canister and dump the water out. If there is any sediment in the filter screen, clean it with some fresh gasoline and reassemble the unit.

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About the author:

Ed Sherman

Ed Sherman is a regular contributor to boats.com, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.

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