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Fuel Gauge Accuracy and Safety

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sproat3
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Fuel Gauge Accuracy and Safety

Post by sproat3 » Tue Sep 16, 2014 11:56 pm

I want to share a lesson learned regarding fuel gauge accuracy that has safety implications.
We ran out of fuel on our 1960 CC Capri when the gauge showed 3/8 fuel tank level. I learned several lessons about checking fuel level before going all the way to Emerald Bay on Tahoe, but being an engineer, I was more interested in getting the gauge to read accurately. First step was to check out the level sender. Upon removal, I found the sender (probably the original) to have broken insulation on the wire to the potentiometer with a bare conductor that was inside the gas tank. NOT a good situation. I'm surprised we hadn't been blown out of the water. I replaced it with a Moeller reed switch sending unit that has no exposed electrical wires in the tank. All electrical circuitry is in a welded stainless steel tube- much higher quality and much safer.
That did not fix the accuracy problem however. The sender and the gauge need to be matched to each other if the impedance ranges are different. To fix that, I found the Fuel Gauge Wizard on E-Bay. After calibrating and installing it, the fuel gauge now reads accurately full scale.
Recommendation: Have the fuel sending unit in your boat checked over the winter. If you have an old sending unit that has an open potentiometer or frayed wire, replace it with one of the newer, safer units now on the market.
1960 Chris Craft Capri (Tahoe Heidi)

kleiner
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Re: Fuel Gauge Accuracy and Safety

Post by kleiner » Wed Sep 17, 2014 7:00 pm

Sounds worrisome. As an aside, if you have a cylindrical fuel tank, it is only possible to get accurate readings at full, half, and empty using a sender and gauge. On the other hand, you can conduct some volume calculations and make a fuel dip stick that provides accurate readings at any level.

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