72 cutlass gas guage needle is off

[topstorey]

I have a 72 cutlass and the gas guage shows "E" as being at a quarter of a tank. If I fill it up then the needle is a quarter of a tank past "F". This mishap has slowly occured since last summer where the needle seems to have slowly moved to the right from empty over a long period of time where it will show the tank being empty. Today it's bordering on 3/8 of a tank at being empty like it's not going to stop working it's way to the right on the guage when the tank is empty. Yes I've run out of gas twice due to this. Does anyone have any idea what's going on here?

[Doug Rodrigues]

The first thing to check is your fuel tank sending unit. When the tank is near empty, it only takes a couple of bolts to unstrap the tank from the chassis. Careful to not pull the wires out of the unit itself. Check for quick connects (typical situation) at the wires near the tank prior to lowering the tank to the ground. The grounding wire to the sending unit will probably be attached near the fuel tank itself to the frame with a self-tapping metal screw (another typical situation). Remove that ground wire and any quick connects leading to the tank. Spray the strap attachment bolts with WD-40 or penetrating oil, and then clean the threads with a small metal brush first before attempting to unscrew the nuts from the bolts. Clean the threads well or the nuts can seize to the bolt threads. With clean threads, the nuts can be removed by hand once you loosen them with a wrench first.

The float in the sending unit has been bouncing around for how many years now? Maybe you'll luck-out and just have to adjust the float arm. Easy to do: With the float sitting on the bottom of the fuel tank, your gauge should read exactly empty, right? Bend the arm to adjust it. Automotive gauges are not very accurate, but you should at least know when empty truly means empty.

Another possibility is that there is a defective resistor at the fuel indicator. I have no idea if your vehicle has such a resistor but perhaps you can look behind the panel to see what is there. If there is a resistor in-line with the wiring to the indicator gauge, make note of the color code painted on that resistor. Go to Radio Shack and have them look-up the resistor value. Use an Ohm meter to check the resistance. If the resistance is too low, that resistor (if you have one) should be replaced. If this were the case, don't even bother with the fuel tank sending unit.

The above is generic advice for most Amercian cars in general. Someone who specializes working on your type vehicle only would obviously be able to give you more specific advice.