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Fuel Filters

Fuel Filters

Q: Your engine has been running poorly, and you suspect it might be due to water in the fuel. How does water get into the fuel, and how do you keep it from getting into your engine?

A: One of the more common ways water gets into fuel is through condensation, especially when tanks are left only partially full. Water also can be introduced during refueling, as well as through faulty fill lines, vents or hoses.

The best way to stop water in fuel from getting into your engine is to install a fuel/water separator filter in the fuel flow between the tank and the engine. (Installing a separator filter isn’t that involved, requiring a couple of fittings and a bracket.) To understand how the separator works, it helps to know a little about the fuel system.

Water and debris settle to the bottom of the fuel tank. Unfortunately, the fuel system draws fuel from the bottom of the tank, so any contaminants can be drawn into the engine as well. As the fuel passes through the separator filter, the water and debris fall to the bottom of its canister, and the clean fuel is skimmed off and sent on to the engine.

The basic canister-type separator filter looks like an oil filter, and the only way to service it is to replace it, though some have a drain in the bottom for removing contaminants. The separator I prefer and recommend is a canister type with a bowl (with drain) attached to the bottom. (Filters for gas inboards will have a metal bowl, outboards and diesels a see-through bowl.) These allow you to maintain the filter by draining water or debris that has collected, and the see-through bowl additionally allows visual monitoring of the fuel system.

Filters are rated by flow requirements and in microns, which refers to the size of the particles it will trap (the smaller the number, the smaller the particle). When choosing a separator filter, its application is most important — that is, diesel or gas, inboard or outboard. If you have any concerns about which filter to choose contact your engine dealer or manufacturer and ask what they recommend for your application.

Fuel/water separator filters should be changed once a year where boating is seasonal, twice annually where the season is yearlong. Of course, you might need to change them more often depending on the condition of the fuel you regularly put in your tank. If you don’t maintain or replace the filter often enough the buildup of water eventually will make its way to the engine. It’s unlikely you’ll have a problem with debris completely clogging this type of filter, especially with a gas engine.

Even the best filters will remove only about a quart of water. If you get more than a quart, or if you get water in your fuel on a regular basis, check your fuel fills, vents, tank and hoses to see where water might be getting in.

Remember, regardless of which separator filter you choose, don’t install it and forget it. Even a small amount of water or debris can make the engines run poorly and ruin a day on the water.

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