Recalibrating/adjusting fuel gauge range

[thechief68]

While I had my engine out for rebuild a couple of winters ago, I took the opportunity to replace my worn out fuel level sender. I was pretty happy I didn’t have to cut a hole in the hatch and it would actually be able to see how much fuel I was had below 1/3 of a tank.

I had also replaced all my tank fuel lines while I had easy access and naturally drained the tank of fuel.

Fast forward a few weeks when everything was reinstalled and I was back rolling, I was somewhat disappointed after my first fill to see my fuel gauge showed an 1/8 under full.

I did see a post on recalibrating the sender (before installation) but saw some references to gauge adjustment screws. Was also considering aging a trim pot in parallel to sender signal but was unsure about the implications on the voltage regulator.

Just wanted to ask the community here if anyone has had success adjusting/calibrating fuel gauge range using the adjustment screws or any other method.
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1977 & 78 Westfalia
2.0L Automatic

[SGKent]

you bend the arm while the tank is out. As I recall the tank reads low, not high. Don't know how a trim pot would fix that. I guess you could build a parallel circuit that lowered resistance by enough to make it full but I doubt if it would be a linear circuit, meaning that it might fix it at full but not at the lower end. Ask Telford that. Also
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George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[rugblaster]

As I recall, the sending units have stop tabs for high and low. I have a a VW issue tool that is a variable resistor. It looks like a mini hose reel, wire leads and clips with the ability to dial in different resistance values on the fly.

In your case, you would use the tool to determine what resistance is "E" and what resistance is "F" on the gauge (using the variable resistance of the tool) and then transfer the values to the new sending unit, again, using the tool. Use the metal tabs on the sending unit for this purpose.

I would try to find someone in your area to borrow this tool from.
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[SGKent]

if this is a swing arm float, the problem is that the original floats were flat topped but the new ones have a flat top and wire holder that goes around them. They never reach the top tab. The arm has to be bent to fool the sender into thinking it is higher than it is. I did a write up with photos a few years ago. You use a yard stick to raise the float while the tank is empty and out of the car. You keep bending the arm until it reads full when raised to the top. Then you lower it gently to the bottom and use a flashlight to see where it sits in the tank, bend stop tab if needed. Then see what it reads on the gauge. You'll have to use a good wire to extend the wires while it is out of the car. Then when you go to fill it, divide what your tank size is by 1/4's and add that fuel and check it. That way you will know roughly how much gas is left at any point. I tried the resistor shunt method and was dissatisfied with the results.

Artists Rendition of original float (flat top)

Float today

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_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"