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Fuel System Checkup


The health of your boat’s fuel system is the difference between a good day on the water and a tow home.

Check your primer bulbs. If they feel squishy to the touch and the engine can “suck” the bulb flat, it’s time to replace them.

Marine fuel systems are a hot topic. Continued pressure from the federal government to increase the amount of alcohol in fuels has brought serious concerns and changes to the marine industry and the way fuel systems are manufactured, rigged, and maintained. E10 fuel (gas blended with 10-percent ethanol) has been difficult to adapt to, but the marine industry has made the necessary changes to parts such as gaskets, carburetor repair kits, fuel lines, pumps, filters, and injectors to combat the ravaging effects of alcohol in the fuel. Here’s how to maintain your fuel system to ward off unwanted effects of alcohol-laced fuels.

Fuel Lines

The engine can’t run if it can’t get fuel. The innards of older fuel hoses are highly susceptible to alcohol deterioration, and if left unchecked can disintegrate and cause clogging, poor running, and even engine failure. The problem is even more insidious because the effects can be highly inconsistent. I replaced the fuel lines in two very similar outboard boats in 2008 using the same fuel line from the same roll. The two boats also used the same fuel. Three years later, I checked the fuel by disconnecting the line and pumping some gas into a clear glass jar using the primer bulb. One boat was fine; the other showed globs of soft rubber from the inner wall of the fuel hose floating in the fuel. Manufacturers generally use 10 years as the lifespan for gasoline hoses, but it’s important to inspect the fuel lines every year, and if there’s any doubt, replace them with new EPA-compliant hose and new clamps.

The EPA markings on this new fuel line show it has an inner liner impervious to alcohol-extended fuel.
Newer fuel hoses have an inner liner to prevent deterioration from alcohol-extended fuels.
Using E15 (15% ethanol fuel) may void your engine’s warranty. 

The new EPA-mandated fuel line (A1-15) uses a very tough inner liner; it’s visible by looking into the end of the open fuel hose. It does make the hose somewhat less flexible; it’s tougher, for example, to push the hose onto a fitting. The new hose is about twice the cost of the older hose. Take care when routing the lines; tight curves will generate kinks and flow stoppages, so make sure each bend radius is at least six inches to prevent problems. Don’t forget to replace fuel fill hoses if you’re doing the others.


Now is the time to replace the fuel filter as well. If your rig doesn’t have a water-separating fuel filter, I strongly recommend you add one. Quality brands like Racor are head-and-shoulders above the rest because they use better components, and finer-micron filters. However, the typical marina brands are fine, too, and work well to filter out water, dirt, and other contaminants. Placement in the fuel line should be between the tank outlet and engine inlet.

Replacing an older fuel filter with a new canister-style, water-separating unit will help keep your boat’s system clean.
Removing and replacing the separating filter can sometimes require an oil filter wrench.

Primer Bulb

Many outboards use primer bulbs; these are damaged by alcohol-blended fuels, too. Inside the bulb is a check valve that can fail and leave you stranded out on the water. If it feels squishy and the engine can “suck” the bulb flat, it’s toast — replace it.

Hose Clamps

The clamps that keep the fuel lines tight are critical and warrant checking. They prevent fuel leaks and, just as important, prevent air leaks. Air leaks can ruin an engine in no time because the fuel/air mixture will become lean (too much air) and the engine will starve for fuel and burn up as a result. Use new quality all-stainless clamps if the old ones won’t hold, are corroded, or are falling apart. Hose clamps are cheap compared to a damaged engine. Be careful about using cheap hose clamps. They’ll rust and fall apart quickly.

Using the correct hose clamps on each joint fitting will reduce the chance of engine failure due to air ingestion.

Fuel Tank

Finally, check the tank carefully for leaks, cracks, and loose mountings. Look for white powder on aluminum tanks, a sure sign of corrosion. Vibration and wave pounding can do a number on your fuel tank, and unless it’s leaking fuel into the bilge, you might not even notice it. I’ve removed tanks that had all the mounting tabs broken or cracked; the only thing keeping the tank in place was the weight of the fuel and the tank/hose connections. If yours is cracked, broken, or corroded, replace it. While a new tank can be expensive, a boat fire is surely worse. When remounting your tank, be sure it’s not sitting directly on the boat floor; suspend it slightly above, or use a nonabsorbent-rubber mounting cushion pad underneath. If possible, create an access hole in the floor so that you can use thru-bolts, nuts, and large fender washers to mount the tank.

Fuel tanks should be held in place with brackets, preferably lined with a rubber cushion.
Fuel cap should be sealed with an O-ring and retained by a chain to keep from losing it overboard.
Note the clean routing of fuel vent, filler, and delivery lines on this installation.

One last word about anti-siphon valves: These reside in the outlet fitting from the tank to the engine, usually threaded right into the fitting, with a hose nipple on the other end where the fuel line is installed. The anti-siphon feature is to keep fuel from flowing into the bilge if a failure occurs in the fuel line. Some cheaper valves can cause fuel restrictions to the engine; if you experience this, don’t be tempted to simply remove the check valve from inside the anti-siphon fitting. Doing so could get you in a heap of trouble if you experience a fuel-related boat fire due to fuel in the bilge. Instead, replace it with a quality anti-siphon valve, available at local marine dealers. Hint: The high-quality ones cost three times as much as the cheap ones, and are usually made in the USA.

John Tiger

Contributor, BoatUS Magazine