Fuel guages always seem to
malfunction. And some engine hour meters will keep clocking hours if the ignition is on the the engine is off. What has been infallable for me is simply keeping track of the hours my engine is running by looking at my watch and knowing the engine's fuel consumption rate. In my case, my Yanmar 2GM20F burns about .2 gph at 2,000 rpm in nearly flat water, .3 gph at 2500 rpm, and .4 gph at 3,000 rpm. If you start out with a full fuel tank and keep doing the simple math, you'll always know just about the exact amount of fuel you've got left -- and never be disappointed when a guage or meter breaks down.