Morris Minor Owners Club

Hello all, I have just got a 1968 traveller. She runs well and apart from a few jobs I am keeping till winter I am happy how she runs. However I notice that when I fill the tank the petrol gauge goes up to the top and sticks there. Not a good plan if you don’t want to run out of fuel. Can anyone tell me what I can do to rectify this, is it a case of slightly bending the sensor arm in the tank or do I need a new sensor, that is if it is down to the sensor. Please help before I run dry, cheers Paul.

Hi Time Traveler, my Moggie also does that, however after a few miles I just tap the the underside of the dashboard with my hand and the needle returns to where it should be. I try not to fill the tank to the brim to avoid the problem.
DaveB

Is it supplied by a voltage regulator? If so, is it working correctly?

'Time traveller' - you say that when you "fill the tank the petrol gauge goes up to the top and sticks there." So, does it drop at all from reading 'full' before you next fill up? I would first check the connections at the gauge end and at the sender.

The gauge when the tank is full and I switch on travels to the full position and it stays there no matter how far I travel, when I turn the ignition off the needle goes down to empty. Hope that this helps with a diagnosis. Thank you.

OK the needle returns to 'empty' when ignition 'off' - as we would expect.
Are you saying that the only reading the gauge gives when ignition 'on' is 'full', irrespective of how much fuel is actually in the tank?

First the theory: If your car is +ve earth then the electrons flow one way, if it has been converted to -ve earth then they flow the other way, but The gauge is not affected by which why they flow, so I shall stick to talking about "power" as a nominal 12 volt supply and not care about which way it is "flowing". When the ignition is switched on, then power is supplied to a small voltage regulator on the back of the speedo, and from here to the gauge. The fact that the gauge is moving means that power is getting there. From there is should go via a green and black wire to the sender unit in the tank. Depending on the position of the float arm on the sender (depending on how much fuel is in the tank) the amount of power returning to earth will vary, and this affects the reading of the gauge. No variation on gauge = no variation from sender, OR a short to earth between the gauge and the sender.

The first thing is to disconnect the wire from the sender and then switch on the ignition. If the gauge still goes to full then there is a fault prior to the sender, if it now stays on empty then the sender is faulty and needs to be replaced. Try that and report back.

Great thank you for being so descriptive as when you’re learning like me the more detail and why that makes it work or fail the better to learn from. I am busy for the next few days but will do what you say and report back, cheers Paul.

If you do the test 'simmitc' suggests, the gauge should read 'full' again if the disconnected wire is then earthed somewhere.....