Yesterday was 'Fuel Off-loading Day 1' . . . I pumped out 40 gallons of gasoline from the boat (so far). At 5 gallons intervals, I checked the fuel gauge to see what its reading was. Each year I pump out until I get air, then I add back enough for fogging of the engines. The next year I start with fresh fuel. anyway, I digress. . .
When I started off-loading fuel, the gauge read 43% (150 gallon tank), so guessing about 65 gallons in the tank (maybe). I recorded the gauge readings as I went.
Pumping out in increments . . .
-5 gallons ( 5 total) / 40%
-5 more gallons (10 total) / 28%
-5 more gallons (15 total) / 29%
-5 more gallons (20 total) / 29%
-5 more gallons (25 total) / 21%
-5 more gallons (30 total) / 6% (low fuel warning)
-5 more gallons (35 total) / 6% (low fuel warning)
-5 more gallons (40 total) / 0% (low fuel warning)
I would expect 3-4% drop with each 5 gallons of fuel removed, so the sender is probably having issues. Since the gauge is now at 0%, I suspect that there is not much fuel left (maybe 10 gallons)
The sender is the WEMA 1306 style, which I believe is a reed-switch sender.
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My plan is to take it out for inspection and resistance testing. I'll also be able to get a look at the tank internals.
When I bought the boat, the fuel gauge readings were a bit strange . . . That has remained so in the conversion from SmartCraft to NMEA2K instrumentation.