We looked at ones with analog readouts by Faria, Isspro, Teleflex, and Wema. We tested these gauges against a simple swing arm sender made by Teleflex, the most common type and the one that probably came with your tank. We filled the tank with 4 gallons (effectively empty), 9 gallons (quarter tank), 18 gallons (half tank), and filled to the top. Here's what we found. At full, all gauges read full. At empty the readings ranged from empty to a little less than ¼. The ¼ readings were from ¼ to slightly over. The ½ readings were from ½ to less than a ¼. None of the gauges consistently measured the correct amounts.
We tested three different types of senders: column, float, and ultrasonic. We used the Wema, Faria, and Isspro column type, the Teleflex floating arm, and an ultrasonic unit from SSI that bounces sound waves off the top of the fuel. We tested them paired with the Wema gauge (on average the most accurate) and the Teleflex gauge (the most common). The three column senders and the SSI ultrasonic were matched by their manufacturers to correspond with the Moeller tank's dimensions. We cut and fit the Teleflex according to its installation instructions. Of all the senders, the SSI ultrasonic was the most accurate and consistent, regardless of the gauge, throughout the four levels. The column senders were about equal, with the Isspro having a slight edge. The floating arm Teleflex was the least accurate.