fuel tank full, gauge says 3/8 tank

[69dodge383]

Got a full tank. Orig fuel gauge says like 3/8 to 1/2 full. Why the difference?? Is the gauge bad ?

Thanks

Doug

[Finn]

Do you have a reproduction sending unit in the tank?

[69dodge383]

New tank and sender...

[John_Kunkel]

Is there a ground strap between the fuel line and the sender?

Remove the wire from the sender and ground it to the frame, then turn on the ign switch....the gauge should climb to full. If it does the gauge is OK and the problem is in the sender/ground.

[Dino]

New tank and sender...

There's your problem then.  The new sending units use a linear resistor while the old one has a non linear one, as does the gauge.  The new unit and the old gauge do not match so you can't get it to read correctly.  You can get fairly close or pick full or empty to be correct but it cannot read correct over the entire sweep.  The best fix so far, courtesy of Charger-Bodie, is to take the sending part off an old one and weld it to the new unit. 

If you're thinking about aftermarket gauges then it's also solved by installing a linear gauge with resistance of 0 - 73 ohm to match the new sending unit.

[Finn]

^That's where I was going with my question.

[69dodge383]

I will get a new gauge. I don't want to pull my tank apart

[69rtse4spd]

Who sells the new linear gauges.

[69dodge383]

I am not sure, can I just by a gauge from summit that will work with what I have??

[Dino]

Any fuel gauge matching the sending unit will work so you're looking for a 0-73 ohm with 0 being full.  You may not be able to find one exactly like that, some are in the 10 range when full so you still may need to alter the float on the sending unit.  The old gauges were not all that precise though so it may work just fine as is.

To be honest, if you have access to an old sending unit, it's way easier to adapt the unit then to stick an aftermarket gauge in the dash.  If you're mounting the gauge elsewhere then forget what I said.

[69dodge383]

I am leaving the orig gauges as is. I will just mount an aftermarket gauge under the dash or something.
I don't mind for it to be off when full. I just don't want to run out of gas!

I will post a couple gauges n a lil while to get some feedback on whatis the best one for me

Thanks

Doug

[69dodge383]

Here is a couple from summit

73 empty 10 full

http://m.summitracing.com/parts/equ-7361

65 empty 10 full

http://m.summitracing.com/parts/vdo-301020


So the first one would read correct when empty but not when full.  I guess the gauge would say that it is full when the tank isn't 100% full...

The second one would say it is empty when not totally empty and the same for full. I don't mind being conservative on the empty side.

Does that make sense? Am I thinking correctly on the readouts vs the actual?

Doug

[Dino]

The fuel gauge system has a margin of error in that the 0 reading can be a bit more and still read correctly, same with the 73 reading.  It can be a bit more or a bit less.  When you move the float on the sender you can see how much play there really is.

The first gauge you linked will likely work just fine, although you may want to look at another brand as I have not heard much good about those.

The second may still work in the ohm extremes BUT look closely and you can see that the hallway mark is not in the middle.  This indicates it is a non linear gauge like the stock one, so that won't work with the linear sender.  You will never get it to read correctly over the range.

Even if the halfway mark on an aftermarket gauge seems centered, be sure that it is linear before you buy it.

[69dodge383]

This auto meter gauge says it is for chrysler vehicles.

http://m.summitracing.com/parts/atm-2642

[Dino]

This auto meter gauge says it is for chrysler vehicles.

http://m.summitracing.com/parts/atm-2642

Must be for Chryslers with non linear fuel gauges like our cars.  I don't know enough about Chrysler to say they are all non linear but that gauge definitely is.  Your sending unit is no longer like that though so linear will be the way to go.