Fuel Gauge Question

[Booker T]

I tried to do a search but could not find anything related to my specific question...although it my be my searchs skills.

I am working on getting all of my original gauges back in my 54 and operational. This includes the fuel gauge.

Right now I have an aftermarket fuel cell in my trunk with no sending unit. I have converted the car to 12v negative ground.

What type of sending unit would I need to find to work with my original guage? I know there are different resitance ranges / types that need to be taken into consideration but not sure what type I need for the original gauge. Additionally, from what I read I will need to get a "runtz" to drop to 6v for the power to the guage. I am guessing that this is still the case as the sending unit is only providing the reading (resistance) to the gauge and there still needs to be power run to the gauge itself (which needs to be dropped to 6v).

Thanks in advance for any help!

[Booker T]

Ok...I have done some more searches using different terms (getting better) and it appears that I my gauge needs a sending unitl that operates on a 73 (or 78) ohm to 10 ohm range.

I don't have my original gas tank, as mentioned above, I have an aftermarket cell in the trunk.

From what I have read it appears that my car will take a single wire sender. I guess that means that my gauge would have 2 connections on the back, once for the sending unit connection and one for power.

So, now I am at a point where I just need to find a universal (adjustable for tank size) single wire sending unit in that ohm range and a "runtz" resister to drop to 6v for the power to the gauge. I have looked at the JC Whitney links and it is suggesting the following for my car but I can't find the ohm range...

http://www.jcwhitney.com/fuel-level-sender/p2007297.jcwx?filterid=u0j1

Oh...I also have a couple different guages sitting around for this car. Does anyone know of a way to test the gauges to see if they work without having a sending unit "in hand"?

[TodFitch]

Ok...I have done some more searches using different terms (getting better) and it appears that I my gauge needs a sending unitl that operates on a 73 (or 78) ohm to 10 ohm range.

I don't have my original gas tank, as mentioned above, I have an aftermarket cell in the trunk.

From what I have read it appears that my car will take a single wire sender. I guess that means that my gauge would have 2 connections on the back, once for the sending unit connection and one for power.

So, now I am at a point where I just need to find a universal (adjustable for tank size) single wire sending unit in that ohm range and a "runtz" resister to drop to 6v for the power to the gauge. I have looked at the JC Whitney links and it is suggesting the following for my car but I can't find the ohm range...

http://www.jcwhitney.com/fuel-level-sender/p2007297.jcwx?filterid=u0j1

Oh...I also have a couple different guages sitting around for this car. Does anyone know of a way to test the gauges to see if they work without having a sending unit "in hand"?

If you have an after market tank or fuel cell it might have a SAE fuel sender 5 screw mount for the sending unit which is very standard for the universal senders.

A "one wire" sender has only one wire connected to it from the dash unit. It relies on chassis ground for the other part of the circuit. You may have to rig a ground wire from the sending unit to a good chassis ground to have it work correctly.

To test the dash unit, pick up some resistors with values close to that needed for reading full and for reading empty. Connect the resistors one at a time between the terminal on the dash unit and ground. See what the dash unit reads. I made up a little box with a number of different resistors in it and a switch to select which one was connected to allow me to easily test my dash unit. I'd loan it to you but it is setup for my '33 which uses a resistance range that hasn't been used on any car that I know of after about '35 or '36.

[Booker T]

Thanks for the info!

I looked at the fuel cell last night and it appears to have the 5 screw mount sending unit you are talking about. So, now I guess I will just need to determine the resistance range on the fuel gauge (starting with 78 and 10 as I read in another post) and then find a universal sending unit in that range.

Thanks for the tip on testing the resistance!

And finally, it seems that since my gauge is 1 wire type I would just need to worry about the ground on the sender unit itself. Oh, and a "runtz" type thing to drop the voltage to the gauge itself.

Thanks again!

[claybill]

i went thru this same thing a year ago...finally bought a matching sending unit and under dash gage from napa..5hole.....$85. gotta be the matching unit..

so now it works fine for full and empty..who knows the in between. satisfied.

bill

[Booker T]

Yeah, I just got a new (used) set of gauges and was looking forward to putting my dash back together. I currently have a oil pressuure, temp and ammeter in the glovebox and no fuel gauge. So, if I can't get the factory gauge working then I will probably just do without. The fuel cell in the trunk is huge and it seems like my car gets really good gas mileage...on my recent roadtrip my friends kept asking if I had done a Prius motor swap!!!

You bring up a good point...the only thing I am really concerned about is the accuracy at the "empty" end of the spectrum...there enough gas stations these days that as long as I know in a 50 mile or so range I should be safe. The in between is not that big of a deal...and as long as I know how to "read" it based on any inaccuracy...has to be better than opening the trunk and peering into the tank!!!

[TodFitch]

...The in between is not that big of a deal...and as long as I know how to "read" it based on any inaccuracy...

Or you can go nuts trying to have it reasonably accurate. http://www.ply33.com/Repair/fuelsender2.html

[JBNeal]

A couple of notes:

The one wire sending units are prone to losing ground continuity since there are several areas of contact that can oxidize. I have had good results with a simple ground stud installed to the sending unit and a separate ground wire run to the chassis ground. The gauge has a responsive needle sweep rather than an erratic needle jump that is associated with ground continuity loss.

To give yourself a little wiggle room, adjust the float so that it does not touch the bottom of the fuel tank. I've adjusted a couple of floats so that they are about 2 inches from the bottom of the tank to show E on the gauge. Once the bouncing needle starts to touch the E on the gauge, it is a warning that the tank is nearing empty; once the needle stops on E for extended periods means that the tank is almost empty. This approach may mean that the fuel gauge may read F for an extended period, but it is unlikely that the gauge will hang on 1/4 F when it is actually empty.

[Booker T]

Or you can go nuts trying to have it reasonably accurate. http://www.ply33.com/Repair/fuelsender2.html

Funny! I had just read over that in the last couple days and almost decided and nice clean stick in the trunk would be a good enough gauge for me!!!

[Booker T]

Well, it seems that the original fuel sender that everyone was talking about (this forum and others) is no longer available from JC Whitney under the original part number (ZX128525U).

Below is what I can come up with doing a search. It is a little more pricey but imagine it will work the same for my application using the suggestions that have been made. Is this the same model with a new price (others had mentioned $19.99)? If not, does anyone know of a source for the other parts (specifically at the lower price as I am cheap!).

http://www.jcwhitney.com/adjustable-fuel-level-float/p2005714.jcwx?skuId=162409&filterid=c2072j1

[Rusty O'Toole]

Chrysler products and Ford products used the same resistance gauge in the 6 volt era. Antique Ford speciallists sell 1935 - 55 gauge senders that are compatible with 6 volt Chrysler gauges and are cheaper than Chrysler senders.

If you do this you will need a voltage drop device, such as Runtz, or a resistor, or a Zener diode, or even a center tap off your 12 volt battery, as a source of 6 volt power.