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TM 9-8000
a reading. The sending unit consists of a hinged arm with
(2) When the fuel tank contains fuel, the float will
a float on the end of it. The movement of the arm
raise the arm, causing the cam to push the grounded
controls a grounded point that makes contact with
contact tighter against the bimetallic strip contact. This
another point that is attached to an electrically heated
will cause an increase in the amount of heat required to
bimetallic strip. The heating coils in the tank unit and the
open the contact points in the sending unit. The result
gage are connected to each other in series. Operation is
will be longer current pulses to the instrument panel
as follows.
gage, causing higher gage readings. The gage reading
will increase proportionally with the float level in the fuel
(1) When the fuel tank is empty, the float lays on
the bottom. In this position, the arm- operated cam
exerts no pressure on the grounded contact. When the
(3) The tank unit will compensate for variations
Ignition is switched on, current flows from the ground,
in electrical system voltage automatically. High voltage
through the heating coil in the sending unit, through the
will increase heating, causing the points to cycle faster
heating coil in the instrument panel gage, and to the
and if the voltage is lower, heating will decrease, causing
battery. The heating of the bimetallic strip in the sending
slower point cycling.
unit causes it to deflect, opening the contact points. The
opening of the points will allow the bimetallic strip to cool
(4) Because the gage pointer is moved by the
and return to its original position, again closing the
heating and cooling of the bimetallic strip, the gage
points. The cycle of opening and closing the points will
reading will not react to sudden fuel level changes
continue, supplying current pulses to the heating element
caused by fuel sloshing. This will prevent erratic
in the fuel gage. The length of the pulses from the
b. Thermostatic Fuel Gage: Externally Regulated
sending unit when the tank is empty will only heat the
(Fig. 17-7). The externally regulated thermostatic fuel
gage bimetallic strip enough to cause deflection that will
move the pointer to the empty position on the gage face.
Figure 17-7 Thermostatic Fuel Gage: Externally Regulated


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