K series Temperature gauge problem

[kirbs88]

Have a 2002 k series supersport seven. The temperature gauge has a life of its own, and will suddenly read very high temperature. This happens when i rev it. engine is not overheating. Changed out sender on the engine, made no difference. Is there a voltage stabiliser feeding the gauge or is it built into it. Im assuming its an electrical problem, because the engine runs perfectly with the electric fan cutting in and out on tick over as normal. Thanks Steve

[CaterBram Jnr]

If i remember correctly when shorted to ground the temperature gauge reads full scale. If you have replaced the temperature sender have you checked the cable route for a trapped wire or faulty connector which could be shorting out.

[V7SLR]

If there's a short it will instantly swing to "full scale deflection" not just high temp, the needle moving at the same speed as it would from zero if you'd just restarted a hot engine - maybe actually short the sender to see what the result would be?
However if from your description it steadily climbs from normal (90ish deg) to quite high (110 to 120 deg) and then steadily drops back down again, and repeats, it's more likely you have an airlock in the cooling system.

[kirbs88]

Have tried shorting the wire out from the sender and gauge goes full scale. Gauge reads about 85C when ticking over, as soon as I move away and start revving the engine, it immediateley goes up to about 110-115 degrees C, just short of the red section. Have check cooling system and thermostate is opening as it should be, and electric fan cuts in and out OK, engine seems to be operating at normal temp, have opened the expansion bottle when hot and no pressurisation, and water is warm but not unduly hot. Im thinking it must be the gauge.

[BertBert]

Looks like you have to do some diagnostics unless anyone has a specific pointer.
The elements are...
Sensor
Gauge
Wiring between
Voltage
Earth (or partial short to earth)

You could wire up the sensor you took out with it out of the car (IYSWIM) and see if the temp (of the sensor not on the car) changes with revs.
You can use a kettle to try the temp sensor on differing temps of water in the kettle to see if it reads correctly or incorrectly.
Perhaps you can plot the resistance of the sensor against heating the kettle and use the resistance of the sensor as a gauge.
You should be able to work out where things are going awry.

Try to eliminate each.
BErt