Estate Fuel Tank and Sender Unit

Date: Jul 2019, May 2022


Fuel needle on dashboard not moving when ignition turned on – possible causes include sender unit failure

Fuel appears under car when filling or stopping – WARNING – fix this urgently

Engine misfires generally especially at high rev’s.



When filling the tank very full fuel appears under the car. Inspect filler tube from under rear of car. As soon as possible, remove the tank to investigate and repair.

Leaks of fuel at rear of car that occur all the time might indicate a rotten tank. Remove tank, investigate and repair.


Tank Sender Unit

When the fuel gauge not moving it is possible there is a disconnection somewhere in the wiring or that the voltage stabiliser (mounted on the back of the dial) has failed.

When the fuel gauge moves to empty or low and won’t go much higher when the tank is filled, this indicates a punctured float. Remove tank and investigate.


Mis-fires can have multiple causes including: dirty fuel in tank being picked up and sent to carburettor. Disconnect fuel line and use a temporary feed from a clean fuel tank to prove the issue.


Getting ready

It is recommended to use as much fuel from the tank first (by running the car as normal – don’t run out though!!). Less fuel is less weight in the tank and less chance of spillage when the tank comes down.

  • Disconnect battery earth (or positive if positive earth) – to avoid any sparks
  • Remove spare wheel
  • Apply penetrating oil to the 8 x tank mounting bolts
Figure: Tank Bolt Location

Apply penetrating oil to filler clips (the one nearer the filler itself will probably easiest to remove.

Apply penetrating oil to breather tube.

Jack car up and put on axle stands.

Go for coffee and let the penetrating oil do its work

Dropping the tank

Release the 8 retainer bolts quarter of a turn to ensure you can remove them without creating any sparks once the filler neck is removed.

Remove the breather circlips x 2 (I guarantee one will be rusted solid so good luck – you might need to cut the clip with a saw)

Figure: Filler Pipe, Vent Pipe and Sender Wire

As said, there is always one:

Figure: Jubilee Clip Cut Through

Slacken the main filler clip. Move the tank on the jack to expose this clip.

Figure: Shifting The Tank A Bit To See The Filler Pipe Securing Clip

Remove filler cap and remove the four screws holding the filler neck to give some wiggle room

Now loosen the 2 bolts that secure the spare wheel brackets in the forward position so these brackets can swing out of the way.

Figure: Removing Spare Wheel Assembly To Make Space To Lower The Tank

Remove fuel line clamp near shock absorber

Disconnect fuel line to pump (should be connector above diff somewhere), unclamp and carefully slide flexi-line off the metal fuel line.

Remove the 4 bolts holding the tank on the rear lip.

Now, prop the tank and remove the 4 bolts securing the tank in place.

Remember you are making a petrol bomb so take great care.

You may need to move the tank about a bit to release the fuel filler hose.

Figure: Tank Off Of Car Ready For Investigation

Removing the sender unit

Clean the top of the tank with an old tooth brush and some paraffin to prevent muck dropping into the tank.

The sender is held in with a lock ring that rotates in and out

Figure: Locking Ring And Tank Sender Unit Ready To Be Removed

My lock ring was in a terrible state so I levered it out in the end so as not to damage the tank or sender unit.

With the lock ring out the sender and fuel pick up assemble lifts out (do this gently).

Figure: Sender Unit Out And Rusty Locking Ring (that will need replacing

The float can be unclipped from the sender.

Shake the float to see if is full of fuel. If there is any fuel inside then replace it.

Put a resistance meter across the unit and check the resistance changes as the float lever moves up and down.

Taking some measurements


Figure: Depth Of Fuel Pick Up
Figure: Diameter of Flange Plate
Figure: Depth of Resistor Block

Electrical resistance across the sender unit

Whilst I had the estate sender off I took some measurements:

Float state20192022
Full93 ohms95.8 ohms
Mid?? 21 ohms ??83.3 ohms
Empty67 ohms73.1 oms
Electrical Measurement

I used different meters between 2019 and 2022, I suspect the 2022 figures are more accurate as I spent a little more time preparing to measure resistance i.e. used a Dremel to clean all contact points and used a higher quality meter.

Figure: Measuring Resistance Across The Unit

Other notes on senders and gauges

It is important that your sender impedance and gauge deflection are matched. I did not experience this issue as my sender was working and failed, however, others restoring vehicles or buying an unknown vehicle may encounter issues with the gauge not accurately representing the fuel in the tank. Of course, a sender can get stuck too so you’ll need to investigate both ends.

2022 Another failure

Figure: Broken Electrical Conductor Inside Tank

To repair the above I soldered a wire strap between the two ends.

Reassembly is basically a reverse of the removal procedure

A couple of recommendations:

  • Paint top of the tank (as it cannot be reached when in place)
  • Check resistance across sender before re-using, refer to measurements above.
  • Check connection of power wire to the sender is good (tank has to come down to fix any problems)
  • Check sender is earthing through tank before inserting back under the car (continuity check sender plate to tank, it connects through lock ring (which you might have pre-painted)
  • Be very careful when lifting the tank not to create any sparks.
  • Don’t forget to tilt the tank in

Checking the tank earth and resistance across sender (tank is approximately half full so 24 ohms is good)

Figure: Checking Resistance Across Sender When Fitted To Tank

Replacing missing lock washers, using some spares that just happened to be in the garage.

Figure: Finding Some New Washers

Below, a lot of blocks in place the tank is presented back to the car. In this case the reassembly is without anyone else to help. Note the slop cloth, this will come out as the filler approaches the chassis rail.

Figure: Refitting The Tank Into The Car

Troubleshooting a known good sender

  • Check you have voltage on the green-white wire coming to the tank. Will be 12v (through stabilizer) – need to double-check this
  • Check tank is earthed well, and re-measure your resistance (it will be at whatever level the fuel is in the tank!!)
  • Check the connection between green/white and green black/wire.
  • The worst case is to take tank down and recheck everything off the car.

The finished product

The meter is exactly where it should be.

Figure: Fuel Gauge Showing Deflection


Approximate prices from: 2019

This is where things get fun, the estate sender locking ring differs from the saloon (oh joy of joy).

I had to contact a classic Mustang supplier as the parts are common.

Mustang ’66 Lock ring, seal and float

C0AZ-9A307-BLocking Ring
Mustang Spare Parts: 64-73 Sending Unit Retaining Ring
Mustang Maniac£8.40
C0AF-9276-ALocking Ring Seal
Mustang Spare Parts: 64-73 Fuel Sending Unit Gasket
Mustang Maniac£4.80
C0AZ-9202-BBrass Float*
Mustang Spare Parts: 64-73 Brass fuel sender float
Mustang Maniac£24.00
Fuel line Jubilee clips x 2 6-11mmHalfords / eBay£3.80
Breather tube Jubilee clips x 2 16-22mmHalfords / eBay£4.83
Fuel filler Jubilee clips x 2 55-70mmHalfords / eBay£4.90
F17Fuel System: F17 – Fuel filler neck hose estateClub Spares£8.00
Green/black classic car wire 1mm (16.5A) x 5m
3m lengths of 1mm² 16.5A cable – 85 COLOURS TO CHOOSE FROM – 12v car wire loom
Electrical bullets and connectors 24 bullets, 4 singles and 4 doubles
(you need the 2 singles and 2 bullets)
classic car wiring bullets for sale
Heat Shrink 4.8m x 1m
Heat Shrink Tube 2:1 Electrical Tubing Sleeve Cable Wire Heat Shrink All Colours
Parts List Table

Remember to add delivery costs to prices.

Mustang Maniac postage £10 (killer price)

*Note: I suspect the new lead-free fuel might dissolve the solder used in the float, the new one lasted 2 years. I have replaced it with a plastic alternative.

Figure: Example Unit With Plastic Float

Note: The above unit I spotted on eBay Ford Cortina Mk3/4/5 Fuel tank sender unit,single pipe,new | eBay It might be worth investigating at a later date to understand dimensions, resistance across and potential to modify to fit.


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