Systems and Engines

Fill 'er Up

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Charles Chapin of Chicago, Illinois, asks:

"I bought my 35-footer 16 years ago and plan to keep it for another 16. Recently I overheard two engine mechanics in my yard talking about problems they’ve had with the new bio diesel fuel. What problems have there been and, more importantly, what should I do to make sure my fuel tank and delivery system remain trouble free?"

Larry Berlin replies:

I’m pretty sure the discussion you overheard concerned problems that might affect some engines if they run on the bio diesel now available for marine use. You always know when you are getting bio diesel, because the pump will be marked with B-2, B-5, B-10; the number signifies the percentage of bio fuel being pumped. Engine manufacturers have anticipated the advent of bio diesel since 2000 and most have designed their engines to run on at least B-10 (10 percent bio fuel); some can even run on a 20 percent mixture. But engines built before 2000 could have problems running on bio fuel. Most of these involve seals, O-rings, gaskets and other parts that are not compatible with the new fuel mixtures. O-rings and seals can shrink and that could produce either a fuel leak or let air enter the fuel system. Unfortunately, you won’t have any warning before these sorts of parts fail.

If there is a chance you will be using bio fuel in the future, you definitely should replace all seals, O-rings and gaskets in the fuel system. Also check the fuel tank, fuel hoses and filters; here again a boat built before 2000 may have a tank, hoses or fuel-filter housings that are not compatible with bio fuel. Older fuel hoses, for example, can delaminate from the inside out and if that happens fuel could be dumped into the bilge. You may be able to spot such problems ahead of time; a failing fuel hose tends to become soft, or may even start to crack. If you see this, change the hose immediately. A good rule of thumb is that you should replace all fuel hoses every 10 years with new Coast Guard-approved hoses.

Bio fuel will also clean out old deposits of sediment inside a fuel tank and this often results in a plugged fuel filter. This problem could continue until either the tank is cleaned or is replaced. You should also replace the fuel pick-up tube in your fuel tank with a stainless steel tube. If the fuel line has pipe joints be sure to take them apart, clean them and then put them back together with a fresh Teflon-based dope. This is also a good time to replace the vent hose for the fuel tank. While you are at it, install an overflow whistle in the vent hose: when the tank is full the whistle will stop blowing and that will keep you from having to pay a big cleanup bill. You should also replace the fuel tank cap’s seal or O-ring. Although I haven’t seen it myself, I have also heard a number of stories about bio fuel softening the inside of older fiberglass tanks, just like the fuel lines. If this happens to your tank and the tank material gets into the fuel system, it could cause problems with the injector, injection pump and even the engine.

Because your engine was built before 2000, you should get in touch with the manufacturer and learn from them what parts, if any, you need to change; have the engine model and serial number ready before you call. If your fuel tanks are fiberglass check with the boat’s manufacturer if possible to learn whether they are compatible with bio fuels. Finally, do your homework on any fuel additive you might use, because some are not compatible with either bio fuels or fuel system components. Don’t use a fuel additive containing alcohol or ethanol until you check with the engine manufacturer. Whatever you do, don’t think luck will get you through this transition period. It could turn out to be a very costly mistake.

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