Water temp gauge calibration issue

[Firestarter29]

I'm a bit puzzled by this. My temp gauge rises to 130 F then stops, it never goes higher even though the actual temp is higher because the ECU-controlled fans start up when hotter. It used to work fine, but not recently.

I've changed the sender, changed the connectors on the sender and gauge ends, checked for resistance - and found a variable resistor in series in the signal lead. I've earthed the signal lead which causes full deflection on the gauge. So with the exception of earthing out, little changes.

I reconnected the old sender (which was fine) put it in nearly boiling water and tweaked the variable resistor and got it up to 150F but no higher (boiling point is 212F for younger readers) even when swapping the wiring about, no higher. I suspect that when the resistor was fitted they earthed out the signal lead then turned the resistor until it went from full deflection to approx 212F but this assumes (if I'm right that this is what they did) that the sensor in boiling water has zero resistance and is effectively a straight path to earth.

I'm sure I'm missing something here, but what ? A search of the TVR forums just got confusing, with talk of caerbont sensors which look like they couldn't fit in the space available.

I've also put a call into Denis, Oglyyoodoo but he hasn't come back to me yet...

[Andy76]

A little knowledge being a dangerous thing all that but, it sounds like a high resistance issue, what's the range of the variable resistor?

What happens with just the sender connected and the variable resistor not connected or alternatively can you find out the resistance range of the gauge?