1) The sensor (photo 1)
The sensor is a hydrostatic fuel sensor-made in the EU. It has four buttons, a trim potentiometer and an LED for calibration. Connection to the dashboard via a Molex connector (supplied). Connection to the ball valve via a brass pressure port.
The function of the buttons is:
Set gauge min
Set gauge max
Set level empty
Set level full
An initial calibration may be carried out with a 1 ½ litre bottle of water on the bench. The details on this are given in the operating manual. Fuel density (DIN 228) is 720 to 775 kg/m3 or roughly ¾ the density of water. Therefore, 33cm water corresponds roughly to a full tank (43cm) of fuel.
Photo 1 – The sensor
The long, sought fuel level gauge for the T-Series cars is now available. This is a hydrostatic level sensor which connects into the fuel tank drain plug via a three-way ball valve. The installation of the ball valve adds a user-friendly drain facility. The arrangement at the bottom of the tank is shown in the drawing, which gives the installation detail.
2) The gauge (photos 2 and 3)
The sensor may be connected to a standard fuel gauge e.g. 240 … 33 Ohms empty to full. I have also tested it on a 10 … 90 Ohms empty to full. As the T-Series was never fitted with a fuel gauge, it was time for a reincarnation. The photos show cannibalized far eastern stepper motor 52mm gauges fitted with more period looking dial faces. The scale is non-linear in an attempt to compensate for the shape of the tank. (The red pointer was later painted).
Photo 2 – Matching colour for MG TD
Photo 3 – Black dial for MG TF
The gauge and the sensor require a +12V … 0V connection. This is not an issue on cars that have been converted to negative earth. On cars that have the original positive earth, it is easy enough to make an isolated floating negative earth supply via the switched ignition, using automotive relays. The details are shown on the cable harness wiring diagram provided. The actual length of cable required depends on the preferred routing of the cable. Approx. 4m (12ft) of cable harness is sufficient. The harness can be covered with polyester cable braid for protection. The corresponding Molex plugs and pins are included in the kit and will require crimping with a pliers. The wiring cable is not provided but specified. The recommended installation point for the gauge is on the dashboard to the left of the Speedo. On RHD cars obviously on the opposite side.
Installing this system as recommended does require carefully drilling a 52mm hole in the dashboard which is not what every owner wants to do.
When we tested the fuel gauge system, we found the sensor clogged, due to unknown rust in the tank. The drain plug is slightly lower than the gauze filter on the fuel line. If you suspect rust particles in your tank, although there is no flow, it may be advisable to fit an inline filter between gauge and sensor – see photo 4. This has been tested and should does not affect the hydrostatic pressure.
Make sure there is no air trapped in the fuel hose between the sensor and the ball valve. This will lead to false readings if not bled correctly. It is best to fill a little fuel in the tank then fill the hose and sensor with fuel in the vertical position, open the ball valve very slightly so fuel just drops out and into a bucket placed under the ball valve. Then quickly fit the hose to the ball valve. It is also recommended to keep the fuel hose as short as possible and no smoking!
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Photo 4 – Installation with filter. The handle on the ball valve was removed on this installation (Photo courtesy of Klaus Harthof)