Road Fuel Level Sender

[Jon magowan]

I have a Bavaria yacht with a ‘Road’ branded fuel level sender. (I think it works via capacitance rather than resistance). There are 6 cables coming out of this device.

My fuel gauge is indicating full permanently.

The gauge has power and is functioning correctly.

There is power at the sender.

If I disconnect the sender the gauge reads empty.

With the sender connected and powered (gauge reading full ) I cannot measure any resistance (open circuit) between the signal wire (yellow) and any of the other 5 cables in the loom.

Any idea where I can go from here ?

 

[AngusMcDoon]

You could buy a new one...

https://www.svb24.com/en/bavaria-fuel-tank-sensor-270-mm.html

 

[Jon magowan]

Thanks Angus,
Do you happen to know if this is a direct one for one replacement?

 

[AngusMcDoon]

No, I know nothing more than what that webpage & its linked document shows which suggests that you also need the new wiring harness which SVB also sells. It says that it's a replacement for your part number which you can see on your posted photo. I presume yours is 270mm as that's also in your photo but you could confirm that by pulling & measuring it.

 

[Jon magowan]

Thanks Angus. I’ll follow that up with SVB.

 

[William_H]

Capacitive fuel gauges are brilliant in concept though surprisingly not seen so much. I had a 1982 (Ausrtralian) Ford which had capacitive gauge worked well. Later models went back to float type gauges.
Capcitive guages are used on all turbine aircraft (kerosene burning) as they have the ability to in effect measure not the fuel level but rather the energy of the fuel in the tank. Fuel expands when hot contracts when cold but so does the coefficient of capacitance. Hence guages are often calibrated in pounds of fuel (kilograms) not gallons and litres.
The other trick you can do with capacitive gauge is to put them in parallel so in roll or pitch one sensor gets more fule over it while the other gets less the average being what you want to know.
The sensor will consist of 2 tubes one inside the other insulated and mounted from bottom to top of tank. Electronics then measure capacitance (more when fuel covers the gap) and converts to a voltage for the gauge.
I would urge OP to check wiring and connections as far as possible as electronics them selves should be reliabel if you can keek water out. ol'will

 

[Jon magowan]

Thanks for the information. Very interesting that Bavaria yachts used a ‘five star’ solution to measure fuel level. In so many other ways the build quality and component quality is somewhat less than that. A regular resistance type of fuel sender would have been more in line with this theme.
I will definitely take your advice about checking the wiring and connections first. It’s an expensive item to replace.