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Q&A November 2006

Q: Why does water get into your outboard’s external gas tank and how can you get it out?

Q: Why does water get into your outboard’s external gas tank and how can you get it out?

A: Through the years we’ve found that water sometimes gets into even new outboard engine tanks. It often gets in through such fittings as the fuel gauge or hose fitting, or through the vent screw that usually is on the top of the cap. Snugging your tank fittings and using a Teflon sealant on those that are threaded will help, although you usually can’t do much with the gauge. I’ve sealed some successfully, but this means you probably can’t use them (a small matter, since most of mine have only worked well for a short while anyway).

Heavy rain and heavy seas cause the most trouble, and we’ve had so much of this on Chez Nous that my wife, Mel, has made custom Sunbrella covers for each tank. A little cover snaps over the fuel hose fitting and the hose connection, covering both from water coming down. This has been a big help.

Sometimes water is in the fuel when you buy it, even supposedly “good” fuel. We’ve found this to be particularly so in the Bahamas, parts of the Caribbean, and poorly maintained marinas here in the United States with old underground tanks. I use a Racor inline filter/water separator (model 025-RAC-02, ) between the tank and the outboard. It’s small and easy to install, and the bowl lets you see what you’re collecting. Water is obvious; it’s a milky sludge on the bottom. I know this is a sign that I need to clean the tank.

Unless I’m having a serious problem, I keep emptying the filter bowl and wait until the tank is almost empty. Then I pour the remaining fuel through a Racor funnel filter (model RFF8C) and into another tank, sloshing it around to remove all the liquid. The filter has a fine-mesh Teflon-coated stainless steel screen that, according to Racor, filters out crud and water from gas and diesel. (If you’ve mixed the fuel with certain additives, such as water absorbers, this may impair operation of the filter, so read the instructions.) I’ve found that this does a good job of removing most of the water.

I’ve wondered whether the ethanol added to fuel would make these filters perform poorly. I asked Racor’s technical assistance department and was advised that ethanol (E10) in the gas won’t impair the functionality of either of these products, and that Racor has tested for this. I also was advised that if you have phase separation from a lot of water and the combination of MTBE gas and ethanol gas you should have your tank professionally pumped and cleaned.

To clean the tanks I make loose wads of paper towel and insert them through the fill hole into the thank using a steel grabber tool. You can buy them at Sears and most tool shops, and you should have one aboard. I sop up everything in there, tilting the tank back and forth so the liquid runs into a corner near the fill hole. When the wad is wet I replace it with another.

Remember that gasoline fumes are extremely toxic, and you should avoid breathing them or any other contact. Looking into a tank can result in a dangerous intake of fumes (and also damage to the eyes) unless you’re very careful. Don’t use a flashlight or any other artificial source of light — in other words, anything that can cause an explosion. There are certified ignition-protected lights, but I prefer to err on the side of caution. Remember that the fumes are highly explosive and that the gas-soaked paper towel swabs are both flammable and explosive. Exercise extreme caution and be aware that you’re assuming risks. Never do this on the boat. Do it ashore where fumes can harmlessly disperse and you can properly dispose of all waste. Properly ground the tank at all times, and take precautions to prevent sparks.

Built-in gas tanks likely will require professional cleaning. Not only is it usually quite difficult for a layman to reach the bottoms of the tanks safely, there is significantly increased risk of explosion and toxic fumes.

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