Gas tank real capacity? Is there an amount before gauge will register?

[Chad Hilburn]

Hey guys, i'm sure somebody has come across this before. In my convertible, I have a brand new tank it's supposed to be nineteen gallons and a brand new dorman, sending unit. Now we all know how notoriously hit and miss these sending units can be now, i've had good luck with dorman.Ones, but there's always a first time. What I'm wondering is when they say a tank has 19 gallon capacity, is it actually more than that like? Does it take a certain amount before it will move the sending unit in a completely new bone dry tank? I'm pretty sure I have an inaccurate sending unit. But i've put fourteen gallons into a nineteen gallon tank, and i'm getting just below a quarter tank on the gauge and I did double check the gauge. I grounded it to the body and it went all the way to full, so it's not a gauge or a connection problem. I was just wondering, is it supposedly 19 gallons? But it really holds a lot more as a reserve of sorts?

 

[pnora]

Hey guys, i'm sure somebody has come across this before. In my convertible, I have a brand new tank it's supposed to be nineteen gallons and a brand new dorman, sending unit. Now we all know how notoriously hit and miss these sending units can be now, i've had good luck with dorman.Ones, but there's always a first time. What I'm wondering is when they say a tank has 19 gallon capacity, is it actually more than that like? Does it take a certain amount before it will move the sending unit in a completely new bone dry tank? I'm pretty sure I have an inaccurate sending unit. But i've put fourteen gallons into a nineteen gallon tank, and i'm getting just below a quarter tank on the gauge and I did double check the gauge. I grounded it to the body and it went all the way to full, so it's not a gauge or a connection problem. I was just wondering, is it supposedly 19 gallons? But it really holds a lot more as a reserve of sorts?

Junk sending unit. 14 gallons you should be around 3/4 of a tank. Meter match can make the gauge read correctly or get a correct reading sender.

 

[Kern Dog]

The sender may be junk, it may just need adjustment.
Note the A body sending unit below. First picture shows how it was right out of the packaging:

The float and arm sometimes are too short and don't allow the float to rest on the floor. With it set as it is here, I could have 2 gallons or more before the float actually moves. You'd need a multimeter to determine what a few degrees of movement to the float arm actually do to the OHM reading.

Without extending the float arm, I don't know a way to alter the readings the gauge will display. One could weld or solder an extension to the arm and reshape it. I have not experimented with it to find out but hey....I'm retired so one day I might. I could do this on a bench using water instead of gasoline. Maybe I'll see over the summer.
Back on point....
The filter sock in the above picture would have allowed the engine to starve and stall with maybe 2 gallons of gas still in the tank. I bent the tube until it touched the floor and was happy with it there instead.
Now, In 2002 I installed a 3/8" sending unit and new tank in my red car. It was never that accurate. With gas spilling out the filler neck, at best it read just shy of 3/4 and dropped from there quickly. The 68-70 has a 19 gallon tank so technically, 4 3/4 gallons from empty should register as 1/4 on the gauge. No. Mine was pretty much always reading at least 1/4 below actual. 4 3/4 gallons....no needle movement. Half tank...maybe it would read 1/4. 14 1/4 gallons should read 3/4 but was now around half and yeah.... full tank was maybe 3/4 on the gauge.
In 2015 I converted to an aftermarket instrument panel, all digital components. Part of the calibration process involved mapping the fuel sender curve. I wanted it right so I pulled the sender and bent the inlet tube like I did in the A body tank shown above until it rested on the floor. It turns out that it was about 1/2" higher than it should be so it too allowed the engine to run out with about 2 gallons of fuel still in the tank.
After calibration, it does read full with a full tank but it still is not linear. If I get 240 miles to a tank, it isn't like every 60 miles I see it drop 1/4. Unfortunately, I use the gauge as a guideline, not "gospel".

 

[eldubb440]

about 65 gallons if I do the math

 

[Chad Hilburn]

Junk sending unit. 14 gallons you should be around 3/4 of a tank. Meter match can make the gauge read correctly or get a correct reading sender.

That is what i figured as well. I think ill get meter match like you suggested. Ive heard of those

 

[toolmanmike]

That is what i figured as well. I think ill get meter match like you suggested. Ive heard of those

Here's a good thread with info. Solved with a Meter Match Fuel Tank Sending Unit/Fuel Float Adjustmet

 

[RJ Squirrel]

Asked this in another thread, who sells a sender unit that actually works?

 

[toolmanmike]

The sender may be junk, it may just need adjustment.
Note the A body sending unit below. First picture shows how it was right out of the packaging:

View attachment 1988116

The float and arm sometimes are too short and don't allow the float to rest on the floor. With it set as it is here, I could have 2 gallons or more before the float actually moves. You'd need a multimeter to determine what a few degrees of movement to the float arm actually do to the OHM reading.

View attachment 1988117

Without extending the float arm, I don't know a way to alter the readings the gauge will display. One could weld or solder an extension to the arm and reshape it. I have not experimented with it to find out but hey....I'm retired so one day I might. I could do this on a bench using water instead of gasoline. Maybe I'll see over the summer.
Back on point....
The filter sock in the above picture would have allowed the engine to starve and stall with maybe 2 gallons of gas still in the tank. I bent the tube until it touched the floor and was happy with it there instead.
Now, In 2002 I installed a 3/8" sending unit and new tank in my red car. It was never that accurate. With gas spilling out the filler neck, at best it read just shy of 3/4 and dropped from there quickly. The 68-70 has a 19 gallon tank so technically, 4 3/4 gallons from empty should register as 1/4 on the gauge. No. Mine was pretty much always reading at least 1/4 below actual. 4 3/4 gallons....no needle movement. Half tank...maybe it would read 1/4. 14 1/4 gallons should read 3/4 but was now around half and yeah.... full tank was maybe 3/4 on the gauge.
In 2015 I converted to an aftermarket instrument panel, all digital components. Part of the calibration process involved mapping the fuel sender curve. I wanted it right so I pulled the sender and bent the inlet tube like I did in the A body tank shown above until it rested on the floor. It turns out that it was about 1/2" higher than it should be so it too allowed the engine to run out with about 2 gallons of fuel still in the tank.
After calibration, it does read full with a full tank but it still is not linear. If I get 240 miles to a tank, it isn't like every 60 miles I see it drop 1/4. Unfortunately, I use the gauge as a guideline, not "gospel".

I chuckle at the aftermarket senders. No where close to the original. That float arm is so short compared to the factory sender. Most of them register close to empty and close to full. I guess that's as close as you need to be. Fill it up and drive 30 or 40 miles before the gauge moves. When it get's down to a 1/4 tank, you had better start looking for some gas because who knows how long you can go before you run out.

 

[toolmanmike]

Asked this in another thread, who sells a sender unit that actually works?

Many of the A Body guys are having pretty good luck with ones for pick ups and vans. They are closer than the repops.

 

[RJ Squirrel]

Has anyone done a fuel gauge retrofit similar to the ammeter/voltmeter conversion that retains the original gauge face?

 

[Kern Dog]

I don't think that the problem lies with the gauge itself...it is the sending unit that deserves the blame.

 

[savoy64]

Asked this in another thread, who sells a sender unit that actually works?

I ordered one from vans auto (1/2 inch pickup) a few years back and have had no problems with it.

 

[drwlcox]

Hey guys, i'm sure somebody has come across this before. In my convertible, I have a brand new tank it's supposed to be nineteen gallons and a brand new dorman, sending unit. Now we all know how notoriously hit and miss these sending units can be now, i've had good luck with dorman.Ones, but there's always a first time. What I'm wondering is when they say a tank has 19 gallon capacity, is it actually more than that like? Does it take a certain amount before it will move the sending unit in a completely new bone dry tank? I'm pretty sure I have an inaccurate sending unit. But i've put fourteen gallons into a nineteen gallon tank, and i'm getting just below a quarter tank on the gauge and I did double check the gauge. I grounded it to the body and it went all the way to full, so it's not a gauge or a connection problem. I was just wondering, is it supposedly 19 gallons? But it really holds a lot more as a reserve of sorts?

Thanks for posting Chad I have the exact same problem happening with new tank and sender. Like you, even tested the sender out of the tank before installing. It read 1/2 with arm in the middle and full with arm all the way up. I’ll look into a different sending unit.

 

[Lappen]

New sender and new gastank, my problems solved thanks to Meter match, did the job

 

[RJ Squirrel]

I am now planning to replace all the bi-metallic gauge mechanisms in my rally dash with modern air-core fitted into the original gauge faces.
No need for the 5 volt transformer. A 10-75 ohm gauge should work well with a repro mopar sender- we will see-

 

[pnora]

I am now planning to replace all the bi-metallic gauge mechanisms in my rally dash with modern air-core fitted into the original gauge faces.
No need for the 5 volt transformer. A 10-75 ohm gauge should work well with a repro mopar sender- we will see-

It will be no different. Its the junk incorrect reading senders that's the problem. The senders do not read correctly throughout the intended range. Another gauge will read the same. Waste of time and money.

 

[RJ Squirrel]

Should read correctly if I fix my OEM sender with the tapered resistor instead of gambling with a repop right?

 

[toolmanmike]

Should read correctly if I fix my OEM sender with the tapered resistor instead of gambling with a repop right?

View attachment 1990866

Cool photo. I always wondered what those crescent shaped senders looked like inside. Here's the other 2. Aftermarket and OEM.

 

[RJ Squirrel]

Fixed and working, thought the gauge was toast but it appears not!

 

[pnora]

Should read correctly if I fix my OEM sender with the tapered resistor instead of gambling with a repop right?

View attachment 1990866

It should as long as it reads correctly.