Fuel/gas Sender problem

[CudaJon]

Chargerdon,

Your response got me thinking about the gas tank size. I'm assuming my tank is 16.5 gallons from the spec of a 73 Cuda.  Other than running to empty is there any stamp or indication as to the capacity of the tank?? - thanks

[JoeGrapes]

I have the same problem as chargerdon. My aftermarket sending unit never reads true. It stays on full for a long time then drops fast. When it's on empty I still have around 5 gallons left. I replace the dash gauge the voltage limiter and all the wiring. I even added more ground wires. When I took the original sending unit apart I noticed the resistance wiring was shaped like and hour glass and the aftermarket one is straight. Could the aftermarket resistance be linear while the original one is not? We can't be the only people with this problem, can we?

[JoeGrapes]

Also my tank is 19 gallons not 16.

[JoeGrapes]

The sending units that YearOne sells are $79 and the units on EBay are $29. Are they that different?

[CudaJon]

Observing the fuel gauge and the resistance, I believe (JoeGrapes) you are correct the original one had to be non-linear. I was thinking of pulling a resistor in parallel noting that my fuel gauge is going down to fast (based on 11MPG) BUT as you mentioned when I have a full tank it does register full so I would hate to have less of a resistance (<8 ohms)  at full. But this proves you point.

The other thing I notice is that if I measure the resistance (car is off and just parked it) the value increases by almost 2 ohms if I measure it 24 hours later. So what happens is when I start the car the needle is suspiciously low but after a while it comes up about another division (1/8) still low according to my calculations but trending in the right direction.

Soooo if I was retired and had some ..... time I would love to attack this problem. Either by redoing the coil inside the sender (as you mentioned as different) or inserting some resistance either in series or parallel to somewhat correct the measurement. You basically have two different devices. The fuel gauge itself is position vs resistance and fuel sender, float vs resistance, ideally these would match and that's (I think) the problem and I would say these values are somewhat different from car to car. The float vs resistance is the one that's killing me since the tank is installed and it's very difficult to get any type of accuracy without some type of guess work.   I think someone would make a killing if they design a better method..... Thanks for reading!

[chargerdon]

Regarding tank size.   I do not know what the original was, but, I have an aftermarket tank that i bought from am-parts.   It is advertised as a 19 gal tank.   

Regarding sending unit price.   I 'believe' the more expensive is a stainless steel unit, while the cheaper one (which is what i bought) is the same as the original ie galvanized steel.  The old adage says "you get what you pay for", but often the more expensive unit is no better, and another adage says " a fool and his money are quickly parted".  I'm 69 years old, i believe the original style will last at least 20-30 years...  i don't need more than tha    Ie..i wont live that long to care.

[TelisSE440]

 
....The old adage says "you get what you pay for", but often the more expensive unit is no better, and another adage says " a fool and his money are quickly parted".

That's for sure... 

[JoeGrapes]

It's been awhile so I don't remember what I paid for it but it's stainless. I drained the tank and filled it exactly half way. Then I adjusted the float arm so the gauge reads half tank. It still doesn't read true from full to half or from half to empty. At least when it reads empty I know I still have gas. I guess I'll just have to live with it.

[CudaJon]

Well that add credence to the non-linearity of the sender.