The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge Adjustment?

In my 59 GMC 100, when the tank is topped off, the needle reads about 2/3. When on E, the tank takes about 12 gallons. I think the tank is 17 gal so there must be a 5 gallon adjustment needed. Is there a way to up the needle to read FULL when it IS full? (I put in a brand new sending unit in the tank, but that didn't fix it.)
Thanks,
-Michael

Disconnect the sender wire and see what it reads. If it doesn't read full, the problem is not the sender.

I had to bend the arm on my sending unit when I installed a new one. It was about the same as you're saying. I bent it down a little at a time and checked it until I was happy with where it read. Now when it's on E I have about 4 gallons left in the tank.

Don't tinker with it. Now you have a 4 gallon reserve.

I had to bend my aftermarket sender float wire to keep it from hitting the side of the tank. I wish I had bent it to read full and empty while I had it out.

Best way to calibrate sender and Ga is on the bench. This will also insure each is working. Power supply pos to ga pos terminal, wire from sender terminal to sender terminal on ga, ground wire from power supply ground to gauge flange and sender flange. Operate float and adjust Ga and/or sender. Be sure Ga needle is not dragging on face. Delicate indeed. When you reinstall be sure guage body is well grounded to dash and add a ground wire from sender flange mounting screw to Body or frame, provided your truck has all the necessary good grounds. No. 1 cause for bad gauge reading is insufficient grounding. Gas gauges on old trucks are always a challenge. You can't trust a new sender or gauge. You must get them working on the bench first unless you are real good or real lucky and a grounding freak.

I have the same problem with the fuel gauge on my 52 GMC. It reads 1/3 full with an empty tank and 2/3s full when the tank is full. I have disconnected with wire from the gauge to the sender and the gauge reads full and with it grounded directly to the battery it reads 1/3 full. I put a temporary jumper from the cluster case to ground and it still reads 1/3 full. The sender checks good on the ohms resistance through its travel. The electrical system has been converted to 12 volts and I am not using a voltage drop resister to the gauge. I tried a "Runtz" type resister and the gauge would only go to the 1/2 full position with a full tank and still not go to empty.

I really would like to get the gauge to read empty when its empty. Does anyone have any other thoughts other than I just have a defective gauge?

You want us to tell you what's wrong? but don't tell you it's the gauge? OK boys, let me say what I already said, but in a different way. A gas gauge (and the fuel sensing system in general), of all the gauges, is the most troublesome, long distance, ground dependent, tricky, delicate, difficult to diagnose gauge.... and then 12V conversion and adding voltage reducers. The gas gauge is old, the sender is old or Chinese new, the wiring is old and spliced a hundred times, the grounds are corroded or loose. If you really want to fix it, get the gauge and the sender away from the truck at least 50 feet and put them on a bench, a table or in an electrical laboratory. Get them working with new short test wires and a power supply, or see that they don't work and find out what is wrong. Calibrate them together to read empty and full and 1/2 empty or 1/2 full. Then put them back in with new wire and fabulous grounds and keep your fingers crossed. If the sender really does read 0-30 ohms, that does not tell you much except it has continuity. Does it read (register proper ohms to gauge) 1/3 when the tank is 1/3 full of gas? Does float go to or near bottom of tank? Does float go to or near top of tank? Does float leak? Are all grounds proper throughout the entire truck? How much gas is in your tank? exactly. There are many variables and the gauge never read exact anyway. Not much gauge needle or float vibration/slosh dampening used. Keep it full and drive on. Fill up every 100 miles, in my case that would be every year.(put Sta-Bil in it). Probably your Gauge is bad! oops!