The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel gauge accuracy issues.

Hi bolters, I have a '53 3100 with original fuel tank. Last winter I put in a new 12 v fuel gauge and sending unit. I mocked up the wiring not installed, and when I moved the float up and down the gauge read as I assumed it should, from E to F depending on float position. But all last summer when I filled the tank, it only read about 5/8 full. I never ran it out of gas, so I don't know where an empty tank would have read on gauge. So this winter, I removed the sending unit and bent the float rod downward so the gauge should show more fuel than it did previously, in an attempt to get a full tank reading with a full tank of gas. Once again I manipulated the float with the sending unit out of the tank, and I got the gauge to go from E to F. But now when I finally had a chance to go for a ride and fill the tank, to my disgust, the gauge reads only 1/2 to 5/8 full. It seems as if the gauge is slightly more off than it was before I tweaked the float rod, by reading an even lesser amount of fuel. I am puzzled. Could there be something in the tank holding the float from going to the top when full? Is it possible that my tank isn't getting full even tho the pump clicks off and fuel sometimes can spill out of the filler neck after I fill it and I believe it is full? Anyone have any idea what could be my issue here? Thanks

you may have the sender "clocked" wrong, allowing the float to catch against the side of the tank

Bill

I believe that due to the bolt pattern, there is only one way it can fit. The float rod is positioned straight across the truck from left to right, so that shouldn't be the issue.

how did you test it when it sender was out of the tank?

was the sender grounded for the test?

I had the power wire running to its terminal and a temporary ground wire from the chassis to the mounting flange of the sending unit, and the gauge read fine according to how I moved the float arm.

Put ithe sender back in place on the tank, and run a ground wire from a mounting screw to a good clean ground.

The sender is back in, and I have a ground wire running from it to a good clean ground. That's why I am so baffled as to why it isn't reading correctly. Tomorrow I think I'm going to take the sender back out and visually look at the fuel level, which should be almost full even tho the gauge reads a little over 1/2, and make sure that nothing is inside the tank that could be stopping the float from rising to the top.

When I put a new universal sending unit in my '38 I had an issue with the rheostat having so much friction that the float wouldn't raise the arm. It also was so light it wouldn't fall all the way to the bottom. I made my own float arm out of a clothes hanger with a longer float leg and put two floats on it. It rose to the top OK but wouldn't fall. I then put a small lead fishing weight on the arm and it worked normally. Several months later I found a good used OEM sender. When I pulled the universal sender out it had raised & lowered enough to loosen it up to the point it would work normally. You may be having the same issue. Pull the sender and immerse it in a container of gas & watch the float to see if it raises all the way to the top.

Tiny, now that is exactly the kind of past experience that I'm looking for. A plausible explanation for what I'm dealing with, that I would have never thought of. Thanks for that insight.

Are you leaving the gauge in place in the dash? I had one in a 1950 that when the needle moved in the dash it would move so far then get stuck on the back side of the divider that has the lettering on it.

Once I spaced it away just a little the needle moved freely from F - E

If you are leaving the gauge in place while testing then this isn't the issue if ti will go to F - E while moving the arm.

The float might be hitting the side of the tank as it raises. It may be clocked right for the mounting screws, but may have to tweak it just a little to keep the float from hitting the side.

Yes Roy, the gauge is mounted in dash, and works fine when I move the float by hand while testing it outside of the tank.

Problem solved! This morning I removed the sending unit and the tank was indeed full, but I noticed that the float rod was angling slightly forward, which was causing the float to hit the "rib" in the front of the fuel tank that's about six inches to the left of the mounting flange. I bent the rod towards the back a bit, installed the sending unit, and now the tank reads full. Thanks for guys for all the input.

That's great news. Always nice when it works. Thanks for the update.

Now to keep my brake pedal from not fully returning and causing the brake lights to sometimes stay on.