Using a late fuel gauge with an early single sender tank...

[TobyB]

So an early tank has one sender, and a late tank has 2-

but all the lookin' I've done on the internets and such seems to
suggest that the GAUGE changed sensitivity when they added the second
sender, and that the early and late senders are identical.

And that's what I found with a meter, too...

And my late gauge, with one early sender and 5 gals, reads 3/4 full....

...sooooo....

anyone been down this path before and figured out a way to get the
2 to co- operate?

Ideally, I'd love to just swap the sender. Practically,
I suspect I'm into modifying the gauge....

thanks,

t

[scottinAZ]

get an early model gauge and be done with it. the late model gauge typically reads fine till about 1/2 tank with the early sender, then stops doing anything. Been down this path, swapping the gauge takes 20 minutes and is pretty foolproof

[nando]

you can't modify the gauge, the resistance level is different, which is what controls how it works relative to the output curves of the senders.

just get the correct gauge.

[jlevie]

Both responses are essentially correct, though it is a matter of the number of turns of wire in the gauge rather than it's resistance. And the suggestions (swap to the early gauge) are also the only viable solution.

[nando]

right, but the # of turns of wire determines the resistance (FWIW, the dual-sensor gauge measures out to 68 ohms). I built a model using the curves from the senders and the gauge/on board 68 ohm resistor (as a voltage divider) and the results are quite accurate, so I don't think my description of the gauge is off the mark.

in any case, it's not something you can easily modify.

[jlevie]

Well, the number of turns does affect the resistance, but it has a much greater affect on the generated magnetic field and thus the torque on the needle. The analogy is good but the theory is wrong.

The fuel and temp gauges are a little more than simple current meters. Each contains an opposing coil that compensates for changes in system voltage. The opposing coil in the temp gauge is driven by the SI board and serves the additional function of buffering the gauge reading.

[TobyB]

okay, thanks, I was afraid of that.

Kind of like running a variable speed DC 220 motor on 110, then, really...

as in, 'yes you could make it work, but really, why not just get the right part in the
first place and save both time and money.'

On the up side, I guess I have a spare sender now.

Anyone got an early spare gauge going... spare?

t

[jlevie]

I've got one, brand new & still in the box. PM me.

[nando]

Well, the number of turns does affect the resistance, but it has a much greater affect on the generated magnetic field and thus the torque on the needle. The analogy is good but the theory is wrong.

The fuel and temp gauges are a little more than simple current meters. Each contains an opposing coil that compensates for changes in system voltage. The opposing coil in the temp gauge is driven by the SI board and serves the additional function of buffering the gauge reading.

lets just put it this way - the voltage output of the senders is affected by the resistance of the gauge.