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MG Midget and Sprite Technical - Electric water temp gauge NMC

The electric water temp gauge on my 1971 MG1300 appears faulty by only going just above the C even after a run.

Before I attempt to remove the gauge, can I test the in situ electric sender unit by shorting the cable to the unit to earth? What result would indicate a faulty sender unit?

The car is the original positive earth but suspect that has no bearing on the result.
Doug Plumb

Doug
You could test the sender with a multimeter on ohms range. I'm assuming your sender is a thermistor which will likely be higher resistance with engine cold and lower resistance with engine hot. I can't find the resistance range with quick Internet search. If its resistance does vary it may have gone "high". You could try earthing the cable to the gauge momentarily (ignition on) and you should get full scale deflection. Maybe connect via 10/ 20 ohm resistor if you have one.
Bill Bretherton

Doug -it could be a failing thermostat--they seem to tend to fail towards cold nowadays
William Revit

It could be the thermostat, as Willy says, but you do say you've been for a run. Did that include traffic?

The gauges rarely fail, and 9 time out of 10 it's the water temp sender.

The gauge is basically just a voltmeter, and I suppose you could see if you get a full scale deflection ie put 12v across the back of it. Bear in mind that era of BMC/BLMC cars had the gauge wired via a voltage stabiliser, but the stabiliser doesn't tend to go wrong.

My money would be on the sender.
Peter Allen

This thread was discussed between 05/04/2022 and 06/04/2022

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.