An Accurate Alternative
Rather than rely on senders and gauges, you can use a flow meter to measure real-time and cumulative fuel consumption. We installed a FloScan Model 9000 and, after a bit of calibration, found that the digital reading of the gallons consumed over a measured 30-mile course was accurate to within 1 percent of actual usage. In addition, with the 9000 communicating with our GPS, we received critical gph and mpg information that allowed us to find the best rpm and trim tab positions for the most efficiency. The cumulative (and resettable) gallons consumed reading does away with the need for senders and gauges, although it's good to keep them as backup. The FloScan gives direct readings, using a turbine to measure the actual passage of fuel. This is the most accurate method. Not far off is what you'll find if you have a Mercury SmartCraft or similar system. Most of these take their readings from the engine's computer, with the consumption calculations based on theoretical flow through the injectors. If an injector is fouled, or there are other issues, the calculations continue as if nothing is wrong and can give false data. Both direct and indirect reading monitoring systems are more accurate than a conventional sender/gauge system. Either way, use the old 1⁄3 tank out, 1⁄3 back, 1⁄3 just-in-case rule, and be aware of intermediate ports along the way that sell fuel. Most of all, keep your towing insurance paid up-no system is perfect.