Most gasoline is formulated for an automobile, which typically consumes a tankful every week or two. With the exception of boat owners and maybe lawnmower owners, nobody worries too much about gasoline going stale. But, as some boat owner will discover this spring, it does go stale.
Dan Margosian, a Senior Research Scientist at Amoco, said gasoline oxidizes, which creates a sludge that jams injectors and fuel lines. How long the gasoline resists oxidation depends on temperature stability (wide temperature swings are not good) and the quality of the gasoline. The cheaper off-brand stuff, he says, should be OK for three months, and the better-quality gasoline, from a major supplier (Exxon, Amoco, Shell, Mobil, etc.), should last six months.
Whatever the case, once gasoline starts to go bad, it goes quickly, and nothing will bring it back. Fortunately, there are several things you can do to help healthy gasoline stay healthy whenever the boat is laid up. First Margosian recommends using a stabilizer, which adds antioxidants to the gasoline. The sooner it’s added, the more likely it will be effective. Always run the engine to get the stabilizer in the pumps, lines and carb or injectors. Margosian also recommends using a premium pump grade (higher octane) because the higher detergent level increases the gasoline’s stability.
Emptying the tank at the end of the season would appear to solve the stale gas problem, but it also increases the chances that you’ll have water in the tank next spring, since an empty tank attracts condensation. Fumes also make an empty tank more vulnerable to explosion in a fire. Leaving the tank half-full invites both moisture and stale gas problems and is also not recommended. Filling the tank is a better alternative, but it should be topped off to only 95% full, since gasoline needs room to expand.
What to Do If Your Gasoline Goes Bad
Even though you can’t make stale gasoline fresh, adding fresh gasoline to bad gas might make it usable. But, then again, it might not, and you could be stuck with an even larger quantity of bad gasoline. It’s also possible that the bad gasoline could be pumped from your boat’s tank and used in a less sophisticated engine. The same gasoline that wouldn’t burn in a zippy 225-hp outboard will work OK in an old pickup truck.
If no one is willing to take the gasoline, you’ll have to pay someone to pump it out of the tank and haul it away. If you only have a small quantity of fuel, you could try calling your county’s hazardous substances disposal unit. There are companies that specialize in disposing of larger quantities. Depending on where you live, the cost to dispose of gasoline can range from $90 to $200 per 55-gallon drum, plus shipping.
Kit Tests for Bad Gasoline and Diesel Fuel
There are two ways to test for bad fuel next spring: You can run your engine until it sputters and dies or you can buy a “Liqui-Cult” test kit. The latter includes 10 syringes and 10 vials of sterile growth cultures that can be used with either diesel fuel or gasoline. There is also a data sheet that helps you interpret the results. The cost is $80, which works out to $8 per test. Contact Metalworking Chemicals and Equipment, 34 Main Street, PO Box 990, Lake Placid, NY 12946. Telephone: 518-523-2355