New fuel sending unit still shows 1/2 tank on empty tank

Unplug the wires from sending unit, gauge goes below empty. Plugged in, gauge only reads full. Short out the two sending unit wires, gauge reads full.

Order new sending unit

Ran tank out to the point where engine was sputtering and I had to change tanks.

Install new sending unit and gauge reads 1/2 tank.

Bad sending unit? Bad gauge?

Also when I pulled the old sending unit out, the brass filter on the end was no longer there, it was just an open line. Did any come with out a filter of sorts, or is it rolling around in the tank.....

Help.

Not the gauge, or it would have been reading oddly before you changed the sending unit.
Did you check the unit on the wiring before you installed it in the tank? You may not be aware of it, but it's always highly recommended (for this reason in fact) that you check your sending units before installing.
Even if they tested it before shipping, it could have gotten banged around a bit. Or a sender might not be perfectly aligned with an old tired gauge and wiring.
But at a half a tank, it sounds like you just need to adjust it.
Or at least test it out of the tank to make sure it's not simply hung up on something.

As for the filter, we call them the "sock" filter and it's not brass in this case. It's a nylon (or similar) mesh material that's very cleverly designed to wick up liquid fuel even at a pretty low level.
It's a slip-fit over the end, but I believe they had some glue holding them on as well. It's not uncommon for them to literally disintegrate over 40 to 50 years. Depends a lot on the quality of gas too I would think.
Probably still bits and pieces of the old one bobbing and weaving around inside the tank.

Definitely pull it out and check it by connecting it to the plug outside of the tank and check the gauge. Bend and tweak not only the arm, but also the stops as needed.

Oh, and yes it's totally possible to get a bad sending unit. As you may have read here, or experienced yourself, these days it's a horrible state of the quality of parts we have available to us. One of the more common phrases you hear around here these days is "just because it's new, doesn't mean it's good" and that holds true especially for things like starter relays/solenoids, alternators, voltage regulators, and a few other common things that we used to take for granted. Oh yeah, starters too.

Good luck.

Paul

Attached is your problem, which is common, and many of us have been caught by it. It is a case of knowing the answer so that you know what question to ask. Until the vendors include a little caveat statement in the box with the snder this will continue to be a problem. I mean, who would think a replacement sender was fundamentally incorrect?
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Mars, Im showing 1/2 full (optimist) with the tank empty so the chart doesn't line up but it does make sense. However, my only question is whats the solution to this issue you have on the chart??
Great stuff, thanks

Im curious as well. I have a brand new tank from wild horses and an in tank pump. Bought it as a complete unit. when full, it reads 3/4 tank. whn it gets to empty I have 1o gallons left.

Got no answer to that one other than to note that in order to read half full the gauge has to be seeing 25 ohms, if the gauge is in order. Even the bad sender will read lower (higher ohms on the sender) when the float is bottomed out. Time to start digging, but assuming the gauge is good, the sender is not seeing 70-80 ohms or so like it should when bottomed out. Take it out and see if you can get ohm readings across the sweep and confirm that the sender itself is correct.

MonsterBIlly said:

Im curious as well. I have a brand new tank from wild horses and an in tank pump. Bought it as a complete unit. when full, it reads 3/4 tank. whn it gets to empty I have 1o gallons left.

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Stainless tank with one of the new sending units or one of their Sherman tanks?

Todd Z.

O have the sherman 23 gal tanks. Not SS. It was purchased right before the SS tanks came out

Made in China.

Yes, similar answer about the 23 gallon tanks. I have one from another vendor and exactly the same issue: Empty on the gauge equals 10 gallons in the tank. Never reads full, only 3/4, and drops to empty right very quickly. This is one of my great unhappinesses with our vendors. You would think after all these years that they would post in the instructions something like, 'For God's sake, calibrate the sender before you spend all day fighting the tank into position, hooking up all the hoses, and filling it with gas." Such a simple thing to include and yet no one appears to do it. Looking back, there are lots of post about that. But who would think to look for those comments. And until you have one on the garage floor ready to go in, you have to need to read those posts. Again, if you know the answer, you know to ask the question. Very frustrating.