<VV> fuel gauge

Dale Dewald dkdewald at pasty.net
Tue Apr 19 13:27:43 EDT 2011


At 12:00 4/19/2011 -0400, Dorairaj Isaac wrote:

>I just took my '69 140 4speed  with a Monza dash from storage.  The fuel
>gauge goes way past full mark when the ignition is turned on. Where do I
>start looking to rectify this?

The following is a reply I wrote concerning the operation of the Corvair 
fuel gauge.  The second paragraph discusses troubleshooting.

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At 21:45 2/09/2011 -0500, Bob Gilbert wrote:

Is that true of our older Corvair gauges or is the variable current caused
by the variable resistor (the sender) changing the magnetic strength of a 
coil - and thereby moving the needle?

This is exactly how the Corvair fuel gauge operates, except that there are 
two coils working against each other. Both coils are attached to the 
ignition circuit and receive battery voltage whenever the switch is ON. The 
coil that pulls the needle towards F (call this the F coil) is grounded at 
the instrument panel and thus applies a constant magnetic force. The coil 
that pulls the needle towards E (call this the E coil) has more windings 
for greater magnetic force and is grounded through the variable resistor 
attached to the fuel tank float. When the fuel tank is full, the resistance 
in the sender is high (either 30 or 90 ohms), which reduces current and 
magnetic strength in the E coil; allowing the F coil to pull the needle to 
F. When the fuel float is at the bottom of the tank the sender is at 0 
ohms, the E coil develops full current and enough magnetic force to 
overcome the force of the F coil; pulling the needle over to E. When the 
ignition switch is turned off both coils lose power, magnetic force drops, 
and the needle remains in the position it is at.

If there is a break in the wiring to the tank sender or failure of the tank 
sender that creates an open circuit, the F coil will not be balanced by any 
magnetic force from the E coil and the needle will swing to the right way 
beyond the F mark on the gauge. If there is a loss of ground on the dash, 
the needle may swing way to the left or operate erratically with the 
operation of the dash lights, turn indicators, etc.

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Dale Dewald
Hancock, MI


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