started learning about Land Rover fuel gauges when I decided to
add a tach to my instrument panel. The large gauge hole that holds
the temperature and fuel gauge was the perfect donor for a tach.
When I went to replace the fuel gauge with a 3 inch round Smiths
gauge, I quickly discovered nothing worked. Suddenly it was time
to learn about Land Rover fuel gauges and sender units.
Fuel gauges are thermal gauges. The more current that is run through
them, the hotter the metal strip that moves the pointer becomes
and the farther the needle travels. Thermal gauges do not care what
the polarity of the current is. Negative or positive earth is the
same to a fuel gauge.
What matters is the amount of current traveling through the metal
strip. A quick way to identify thermal gauges is that they take
a few seconds to read properly after you turn the ignition on. Some
gauges are designed to have the needle point all the way to the
right when there is minimum current flowing, and some gauges are
designed to have the needle point to the right when there is maximum
current flowing. If you don't match the gauge to the sender unit,
it will read wrong AND read the opposite direction as the sender
is trying to indicate.
The sender unit
A sender unit is a variable resistor whose resistance varies by
the height of the float. Electricity flows from the battery, through
the gauge, to the sender unit into ground and back to the battery.
Remembering that the gauge reads the amount of current flowing
through it. The sender units limits the amount of current going
through it by how high the float level is. The variable resister
on the sender unit can be built to pass maximum OR minimum current
when the float is in the empty position. It is important for gauges
and sender units to be matched.
Land Rover fuel Gauges
The series cars have two types of gauges with matched senders.
One is for the positive earth Land Rovers and one is for the negative
earth late IIA and series III Land Rovers. They read in opposite
directions from each other. Therefore you must be careful to match
the sending unit with the gauge.
The early style sender unit has a small metal tower on the top.
The later style sender unit has a flat top with everything mounted
below the top. They are physically interchangeable on the petrol
tank but must be matched to the correct gauge. The after-market
Lucas fuel tank sender unit replaces the series III sending unit
and will not work with the early gauge.
Moving away from factory stock
When I installed a tach in my instrument panel's large double gauge
hole, I added a 3 inch fuel gauge on an auxiliary panel. Later,
when I installed multiple fuel tanks, I added matching fuel gauges
to monitor my fuel supply.
There are a number of Smiths 3 inch fuel gauges available from
various British cars that would look "factory" on a Series I - IIB
Rover's instrument panel. I used gauges from a MGB.
All of the non-Land Rover Smiths fuel gauges I have tried work
with the series III sender unit and a voltage stabilizer. The earlier
positive earth sender will not work with any other Smith gauge that
Since Land Rovers factory wired for positive earth do not have
voltage stabilizers, I added one to my car to provide the correct
voltage to my Smith's MGB fuel gauge.
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