The Bad News
Our testing was done on a stable platform that wasn't subject to bow rise or internal turbulence caused by typical operating conditions. Even under ideal conditions, we confirmed our original assumption: Fuel gauges and senders in marine applications are unreliable. Put them on a moving boat, and you have more trouble. One bright note: The SSI ultrasonic sender, when properly matched to the tank, gave the best results.
The Good News
All is not lost, however. The old, reliable, low-tech dipstick will never let you down. To accommodate the stick, remove the existing sender and use Moeller's standard five-hole blank plate to cover the sender hole. It should be drilled and tapped to accept a 1½" OD nipple. Next, drill a hole in the deck directly above the old sender hole and install a standard gas-fill deck fitting. Connect this to the new tank fitting with 1½" fuel hose. For accuracy, sounding the tank with a stick is best done while the boat isn't underway. The stick itself can be divided into eighths or quarters and shouldn't be painted or coated because the wet reading is easier to see on dry, unfinished wood. If you're stuck with a gauge, bulletproof the electrical connections. Float senders take their measurement by creating resistance. Check yours with a meter on the two connectors. Senders generally operate between about 30 ohms (full) and 240 ohms (empty). All connectors should be protected by heat-shrinking and coated with a dielectric silicone grease (available at Radio Shack). Every second season take the sender out and see if it moves smoothly and isn't gummed up.