When you’re buying a used boat, you may decide to do the full inspection yourself, or hire a marine surveyor to confirm the boat’s condition. Either way, one of the more difficult tasks is to judge the condition of the boat’s fuel system. Water in gas, particularly ethanol-boosted gas, is quite common in pleasure boats that go unused for prolonged periods. The ethanol actually attracts moisture, which is why tanks should be topped off during storage periods, leaving less room for condensation. Water can also intrude into any boat through poorly sealed fuel caps and vents.
Microbes that feed on hydrocarbons and cause sludge can only flourish if water is present. These same algae emit sulphuric acid as a waste product, which corrodes tanks, pumps, and injectors. In diesel engines, too, given that 90 percent of all problems are fuel-related, fuel system inspection should be an area that gets close attention.
Water or debris in the fuel can be an indicator of deeper problems, namely lack of maintenance, or fuel tanks that are contaminated. So, when a surveyor gets onboard for an inspection he will typically check the condition of engine hoses and fuel filters prior to running an engine. However, some boats that are serviced at layup may show new hoses, clean bowls and filters, yet still have problems in the fuel tanks. When running the engine, look for black smoke, lack of power, or hesitation in acceleration as further indicators of fuel problems
A surveyor should check for water in tanks by using a water-indicating paste, and whenever possible visually inspect the inside of tanks. After running an engine, he should also recheck the filters.
Simply adding products like Biobor to a fouled system will only bring the problem past the filters and into the engine. Biobor and similar products should be used as preventatives, not cures. The only real cures for fuel contamination are to completely replace the fuel and dispose of the old fuel properly, or hire a company to do fuel polishing (filtration) along with a thorough tank cleaning. The presence of algae, discoloration, or sediment should not necessarily kill a sale, but you would be prudent to request that the owner pay for fuel polishing or tank cleaning from a reputable professional.
The worst case scenario is finding that you’ve bought a boat with corroded tanks that need replacing. This will be an expensive problem, particularly if they’re baffled custom tanks, or, as is the case in many pleasure boats due to the manner of construction, require that the decks be cut away.
So when you’re thinking of buying a used boat, any extra time you or your surveyor take to make sure of the quality of fuel will be time very well spent. Good hunting.
An earlier version of this post was published on Boat Trader in 2011.