Fuel and water sensors ?

I need a little assistance on a few items if anyone can help
I need to accurately set up the fuel gauge and water gauge

1/. I have a Lucas fuel gauge with a CA ( Caerbont automotice ) lever arm style fuel transmitter in the tank.
When the arm is set up, which it is, does the gauge automatically read empty to Full as the arm travels up and down with the fuel level. There's no calibrating to do is there ?.

2/ The Lucas water temp gauge is 0-140 deg C. The engine runs and exceeds the 140 on the gauge but the fans dont come on. With a thermometer gun the rad it's showing 90's and if it gets to the tempreture set on the switch in the rad it cuts in about 98 they do come on. The fans work well so it's not them.
As the tempreture sensor was fitted by someone else in the hose next to the engine.
Is it possible that the sensor is not matched to the Lucas gauge ?
I always set up the fuel gauge with the float or sensor about 1/2" or so off the bottom of the tank, gives one a bit of reserve, and most senders have a sliding assembly where the float swings to accomplish this. Its also possible to just bend the arm a bit to get the whole thing to work. Otherwise the sweep is probably pre-set but I have seen small stops top and bottom that can be bent to adjust them. Do a dry run outside the tank.
On your temp gauge check the supply voltage, Smiths gauges are made to work on 9 volts so 12 volts will give a high reading, I would bet yours is the same, and you may need to get a "Voltage Stabilizer" which is another name for a bi-metal strip that vibrates on and of to reduce the voltage. It can also be done with a small voltage regulator available at the local hobby place, and is much more accurate and doesnt interfere with the radio.
If you find that you need the reduction I think I have the circuit somewhere.
One last thing, is that sensor body properly grounded in the hose mount?
Good luck
Last edited:

Ian Anderson

Lifetime Supporter
On the temp sender was ptfe tape used on the threads? If so it will not have a good ground. Likewise if fitted in a pipe is the pipe grounded?

I,ll go over the fuel senders again as for the water temp sender, I have a separate earth attached to the chassis.
The water gauge does rise as the engine temp rises but goes of the scale but the engine don't seem hot just normal engine temp, that's what made me think its the sender incompatibility to the gauges.

I,ll also chat to sgt Monday but as its a weekend I thought I,d ask

Thanks so far..
Checked out the possible problems and found out as suggested that the smiths gauges are 10 volts and by having 12 volts on them gives high false readings.
I have ordered voltage stabisers for the water temp gauge as well as the fuel gauge which could also be part of the fuel problem I have.
Results to follow !!!
As a precaution I have ordered the Smith water temp sender as well.
Problem solved, look at my build log for the findings.
Anyone fitting period smiths gauges should take this into account