I bought a new aftermarket fuel tank sender for '57 Studebaker Hawk, it has the pick up tube built in. The ohms rating is supposed to be 240 to 30 but the new one reads 266 to 30. My gas gauge only reads 3/4 full with a full tank and I have tested it with 2 gauges. Is the low reading because of new sender?
^^^^^!!!!!^^^^ Float travel may have something to do with it. Did you lay the new unit on the bench beside the old unit and measure float travel both up and down to see how close the travel on the new one matched the old one? The float may be hitting the top of the tank before it reads full. Did you check the ohm reading through the travel of the float?
Ohms can play a big part no doubt, but the easiest way i've found is just hook it up fully wired and run the float up and down manually while watching the gage--a little bending here and there normally puts it right on. I make mine a little low just to be sure i have gas when it reads empty. You must ground the sender to the body/frame.
I doubt you can get it to work perfectly with the ohm range off. But all that really matters is on the low end of the gauge. If you test it on the bench hooked up to the gauge you can see where the error is and may be able to adjust the float so empty is really empty. Who cares if full is 3/4 or 7/8?
If the float ends up laying on the tank bottom before it gets to the end of it's down travel it will not show empty. Better to show empty than full if you have to make a choice.
See if you can bend or trim the length of the float arm. The longer the arm, the shorter the degrees of swing between 'the bottom and the top. So by slightly shortening the float arm, maybe with a touch of bending, you can get a full range of swing that doesn't prematurely bump the tank top and stop at a "3/4 full" reading.
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