A friend of mine is an old car collector,  One of his old Packard's  has a condition common to many old cars with the fuel gauge indicator.    the float in the tank moves a lot due to the old style tanks I suppose.    it causes the indicator on the dash to sway up and down as well while making turns and such.

 

 We were wondering if there is a circuit that can be added across the gauge to dampen the voltage fluctuations so it reads steady yet still gives a accurate level of fuel on the indicator.

 

 I was thinking about something with a capacitor and resistor with a time constant that discharges the cap slow enough to keep the gauge at a steady level yet quick enough indicate the fuel level going down. 

 

 It is a 12 volt positive ground system.  

 

   Thanks    

I am no car expert but I do own an MGB so I feel for this mans electrical woes. I read about some people having the same problem with English cars and the fix was to add a resistor somewhere before the wire that goes to the gauge. I think the resistor slows down the signal so that the needle doesn't jump around like a Pogo stick. Perhaps an electrical engineer will chime in and comment.

You could start with a 1 micro farad between the terminal on the gauge to ground.  That should delay the voltage drop.   Up the cap size until you get the desired result.

 

Option 2, get a Raspberry Pi variable voltage divider with a couple optos, measure the output from the tank and average the values over 10 or 20 seconds and supply it to the gauge with a regulator.  It'd be as rock steady as a modern vehicle.  You'd have to transform down the car 12v to 5v for the board, but other than that, it's a very doable solution as well.    

 

There also may even be a way to adapt something from a more modern vehicle (say 70s-80s) and just insert it in the circuit.

Can also look into Anti Slosh Foam kits for fuel tanks. http://www.ksrfoam.com/Gas_tank_foam_.php and its MIL SPEC! lol

You could start with a 1 micro farad between the terminal on the gauge to ground. That should delay the voltage drop. Up the cap size until you get the desired result.

 

Option 2, get a Raspberry Pi variable voltage divider with a couple optos, measure the output from the tank and average the values over 10 or 20 seconds and supply it to the gauge with a regulator. It'd be as rock steady as a modern vehicle. You'd have to transform down the car 12v to 5v for the board, but other than that, it's a very doable solution as well.

 

There also may even be a way to adapt something from a more modern vehicle (say 70s-80s) and just insert it in the circuit.

Malsua has it right with option 1. Cost of about a buck, and a few minutes labor.

Reset trip odometer every time he gasses up. He should know how many miles he gets from a tank within a margin of error.