If your sender is like mine, it works as a variable resistor (aka potentiometer) from 33 to 240 ohms. The higher the resistance, the lower the fuel level. You can disconnect the wires from the sender that is atop the fuel tank and hook up a multimeter set to the 200 or 2k ohm range to take a reading. If you get a reading of, say, 120 ohms, the tank is approximately half full, and you should check the wiring to the gauge to make sure there is not an open circuit (broken wire).
I would expect the gauge to drop to empty when power is removed from the gauge by turning off / removing the key. Your description seems to me to indicate there's an open circuit somewhere. With the key turned on, if you take the top wire off the sender and ground it to something, the fuel gauge should swing to "empty". If not, that would confirm the wire to the gauge is broken somewhere, or there's a busted connector. Note that if the sender is bad, or flaking out, it may be more useful to use an analog multimeter. On my boat, Persephone, the fuel gauge needle jumps all over town; when I used my digital multimeter, the readings were all over the place and it was difficult to get an idea of what was going on. I bought an analog multimeter and the needle on the meter acted just like my fuel gauge, which allowed me to narrow the problem down specifically to the sender. Note that analog multimeters can provide notoriously inaccurate measurements unless a quality (thus relatively expensive) meter is purchased, but for a simple test like I needed, a cheap one served the purpose. On that note, can anyone give advice on replacing the sender? I picked up a replacement Teleflex sender, and it comes with a gasket, but I'd appreciate advice even though it looks simple. Is it true that diesel fumes are not as explosive as gasoline fumes? The Teleflex instructions don't call for any special sealant or "liquid gasket" but is that a decent idea? Finally, can anyone recommend a cutting wheel for a Dremel to cut a bit of the fiberglass above the tank so I have room to remove and install the senders? (The sender was clearly pre-installed to the tank before the tank was fiberglassed into place...) David Persephone, 1988 hull #6480 (Now at home in our slip at Montrose Harbor, Chicago!) PS -- our transit from Racine, Wisconsin to "home" happened this past Wednesday, with winds from 10 to 25 knots the whole ride. We stuck with just our main and the motor to assist, and we cleared 6+ knots the entire ride and had a blast! On Fri, May 7, 2010 at 9:57 PM, Michael <[email protected]> wrote: > > > I've run the engine for approximately 20 hours and my gauge still reads > close to full. The gauge goes down to "empty" when the key is disengaged and > to almost "full" when I turn the key. Is it possible that I would be > anywhere near full after approx 20 hours of use? Is there another way to > tell how much fuel is in the tank without filling it to the top? Any > thoughts or suggestions would be appreciated. Thanks > > >
