Temperature gauge goes straight to hot [FIXED]

When it happened: 30°C outside, I had windows down and AC off.
Sudden hot air came through vents and temperature gauge was above "hot mark".
I quickly parked in shadow and let engine cool for 30min, temp. gauge was still stuck at the same spot, even when power was off.

Update:
After disconnecting & reconnecting battery the gauge drops to cold when power is off.

Old termostat didn't "open" when tested in hot water. New one refitted with new coolant temperature sensor as well.

Temperature gauge still goes all the way up after ignition is on.

New temperature sender sensor installed - red circles in the pictures below.


2nd Update:
Ye that 2nd sensor fixed it. Thanks for all the help

Dom

Still hot after a day! Surely some problem with the reading rather than the engine. I'd suspect temp sender which is screwed into head somewhere (do a search on this site, someone will have done it before)

grogee said:

Still hot after a day! Surely some problem with the reading rather than the engine. I'd suspect temp sender which is screwed into head somewhere (do a search on this site, someone will have done it before)

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gauge is functional, must be one of the sensors. thermostat it k.o. I hope nobody else will have to waste so many hours searching for this problem just like I did.

Engine temp still reading hot after being off for a day!?

Not a chance

If the temperature gauge is going straight to hot on ignition on, it could be the sensor or its wiring being short circuit. I'm no expert, but I believe earlier cars (non digital mileage) used a separate sensor for the temperature gauge, whilst later cars just use the engine coolant for the gauge.

John Woodward said:

If the temperature gauge is going straight to hot on ignition on, it could be the sensor or its wiring being short circuit. I'm no expert, but I believe earlier cars (non digital mileage) used a separate sensor for the temperature gauge, whilst later cars just use the engine coolant for the gauge.

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Mine is '98 model. 2 coolant temperature sensors - ECU temperature sensor below "spark plugs box" and temperature gauge sensor right below the previous sensor. I changed the first one when I was fitting a new thermostat. It did not fix the problem but now the gauge goes down when I turn off the engine.

The gauge temperature sensor must be faulty (i hope). I bought a new one but fitting it there seems hard due to almost no space for fingers, so any help is welcomed. Pictures above

Dom