Temperature gauge reading low?

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blackers
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Temperature gauge reading low?

Post by blackers » Tue Jul 03, 2018 2:12 pm

Afternoon all.

Still a bit new to the forum, so please excuse me if this has been discussed before.

The temperature gauge on my GTC suddenly started reading low. It still works, but seems only to use the lower end of the dial now.

I've replaced the sender unit and also the voltage stabiliser.

Do I take it if it's still showing low, it is most likely to be the gauge itself?

Any other suggestions welcome

John B


John B

1981 GTC (188)

Previous 1971 Se5, 1978 Se6

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Temperature gauge reading low?

Post by philhoward » Tue Jul 03, 2018 2:22 pm

The most unlikely is ironically the gauge - it's a bi-metallic strip and whilst it might gradually read lower over many years, it generally doesn't have a step change. Observe the actual temperatures of the radiator hoses when warming up - if they (and the radiator) warm up gradually, it's likely to be the thermostat. It should get 80 degrees or so on the gauge, then get warm/hot within a minute or two.

Assuming the cooling fan works, when does it kick in? If it's at lower than 90 degrees on the gauge, it's the gauge circuit (sender/stabiliser/gauge/wiring). If it kicks in around 90 degrees, then it's probably the thermostat.


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Temperature gauge reading low?

Post by blackers » Wed Jul 04, 2018 9:58 am

Phil,
Thanks - I'll check it over.

I'm planning on replacing the water pump and stat shortly, so will see how things are after that.

It was a low mileage car, and has had a couple of periods of 'resting', so not sure if that is contributing or not.

John B


John B

1981 GTC (188)

Previous 1971 Se5, 1978 Se6

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Roger Pennington
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Temperature gauge reading low?

Post by Roger Pennington » Wed Jul 04, 2018 10:29 am

A "quick & simple" check which might be worth trying (with ignition on):
1. disconnect the sender wire ( = infinitely high resistance) then the gauge should (as you would expect) show zero.
2. short the wire out on the block, head or manifold ( = zero resistance) the gauge should go to max.


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blackers
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Temperature gauge reading low?

Post by blackers » Wed Jul 11, 2018 11:23 am

Thanks, I'll give that a go.

I have a sneaking suspicion the thermostat is stuck open.

The gauge reads just over 90 when the fan kicks in - logical when you see it written down in posts.

Regards

John B


John B

1981 GTC (188)

Previous 1971 Se5, 1978 Se6

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Temperature gauge reading low?

Post by giddo » Sat Jul 14, 2018 1:44 am

Recent over heating of my GTC has caused me to to be pleased I found :-
http://www.scimitarweb.co.uk/scimiwiki/ ... alibration
My guage was reading high so here's what I did >>>> some of those cheap multimeters that read Volts, Amps Ohms etc also have a temperature range and thermocouple on a length of wire. Remove the sensor from the head, balence an electric kettle under the bonnet and put the sensor - still connected to the car's loom in the water together with the thermocouple. ( You'l have to contrive an earth connection from the body of the sensor to chassis - possibly a pair of croc clips on a length of wire ). With the glovebox removed I was just able to get a hand in behind the dashboard to undo the clamp holding the temp guage, hopefully the wires will be long enough to adjust the guage as in the link above. Get an assistant to switch the kettle on & off to get a temp of 90deg, adjust the guage to match. I did mine three times @ 80, 90 and 100 see photos
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