gas guage operation. How does it work?

[Jack Steele]

Does anyone have a description or schematic of how a gas guage operates.

Thanks for any information.

Jack Steele
Florida

[Mark S. Lovejoy]

What year? *NM*

[Jack Steele]

Re: What ye1955 vette of course *NM*

[Terry F.]

Re: gas guage operation. How does it work?

Variable resistor on a float. Wrapped resistor wire is burried in some type of resin. The assembly is flat and has a tab that drags up and down depending on a lever arm that has a float attached to it. There is only 1 wire attached to the assembly so it is as simple as that. Current travels in and drops across the wire resistor. Occassionally, gunk will build or the metal contact will loose its spring and you will get intermittant continuity through it or the resistor wire will break and the gauge will give you a goofy reading depending on whether the contact is above or below the break in the resistor wire. Hope that makes sense and helps you out. Take care, Terry

[Terry F.]

Re: What ye1955 vette of course

I must clarify that my experience is mostly with C3 and C2. I have no clue as to what was going on in 1955 but I suspect it is similar. Terry

[Mike E.]

Description? --Poorly!

Couldn't help but be a little bit of a smart aleck. Best description of how a C1 gas gauge works is: poorly!
Jumps when you don't have a dedicated ground (so it jumped from the factory when you turned on the lights or hit the brakes or operated the turn signals.)
Not the greatest GM ever invented.

[Jack Steele]

re 55 gas gauge

Hi, Is the two windings in the guage grounded together in the middle where they connect to each other?

[Las K.]

Re: Description? --Poorly!

Mike, I think that this is what's called the dancing gas gauge. Where do you connect the dedicated ground? Should it be from the gas tank?

[Jack Steele]

re bench test.

How does one test that the guage is really working, aside from bench wiring it to a battery and a sender.?

Jack

[Billy Olson]

Re: re bench test.

I've never really understood the logic behind having ANY sort of electrical potential in the gas tank (fuel level senders or pumps). I realize that inside the tank they are supposed to be submerged in the fuel which will not create an explosion or fire, but it seems that if the right combination of circumstances (i.e. leaking tank, incorect venting, sloshing etc.)occured you could get a fuel/air mixture within explosive limits in the tank. It'd be a perfect thing for Mythbusters if they haven't already tested it.

Billy

[Jack H.]

Yes...

The way most gauges work is by having a fixed inductor pulling the pointer needle one way and an opposing inductor pulling it the opposite way. The active side of the gauge typically runs through a variable resistor (gas tank sending unit in this case) to vary the current through the inductor and change the magnetic field strength on the pointer needle in lock-step to resistance of the sending unit...

[Richard M.]

re bench test.

On the bench, battery+(12v or 6v on a 55?) on it's + terminal, and hard ground the sender terminal. It should peg the meter.

To check it linearly, you'd need a potentiometer(i.e. a volume control) between ground and the sender terminal and it should travel accordingly. Not sure what value pot you'd need, but it'd be likely zero to some low ohms value like a sender is. Ideally a known good sender could be used on the bench as well, but that's probably what you're trying to diagnose.

Rich

[John H.]

Re: re bench test.

Here's a schematic of the C1 and C3 fuel gauge circuit, showing the opposing coils in the gauge and the variable resistor in the sending unit; pretty simple system. C1 and C3 are identical except for the resistance value in the sending unit - C1 is 0 ohms empty and 33 ohms full, and C3 is 0 ohms empty and 90 ohms full. The arrowhead in the gauge and in the sending unit indicate ground.