Thread: Temp light on but gauge on zero

Did it mean that there was no oil pressure cause the temp had hit the roof?

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I take it you did check the coolant level?

The temp gauge measures the water temp, hence, no water going past the sensor, and it will read low.

If the levels are ok, you might have an airlock in the system.

Failing that, then I would be sus as to the gauge. Check the connectors at both ends for loose connections before writing it off thou.

Means it went very hot.
When the temp gets above the sensors range the light will come
On and gauge drop to nothing.


"Where the Desert meets the Sea"
'Did I mention some great 4WDriving is just 5 minutes from home?'

Thanks guys. I've got to the river for our holiday without the light coming on again, I will recheck all my fluids tonight when the heat passes (42degrees ATM). I think I was just working it to hard in such hot conditions.

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Keep a look-out for signs of a leaking head gasket. Even if it wasn't leaking before, there's a high probability that it will start leaking soon.

From RAVE ...

In the event of an ECT sensor signal failure any of the following symptoms may be observed:
l Difficult cold start.
l Difficult hot start.
l Driveability concerns.
l Instrument pack temperature warning illuminated.
l Temperature gauge reads excessively hot.
l Temperature gauge reads excessively cold.
In the event of component failure the ECM calculates coolant temperature from the fuel temperature sensor signal. If this occurs, the limit engine operation if coolant temperature is too high becomes inoperative.

The MIL will not illuminate in an ECT sensor failure.

So ... if you check your coolant, and you haven't lost any, it could be a temperature sensor failure/fault ... check the wiring at the sender.

Loaded mid 30's at 110 is not what I'd consider excessive for a Td5. If it got that hot it would have unloaded coolant ... and you'd know about it !

Further more, RAVE goes on to say ...

If the engine coolant temperature gauge receives no input or the input is out of range the
temperature gauge will read cold and the high coolant temperature warning lamp will be illuminated.
The input signal is a PWM signal from the engine coolant temperature sensor via the ECM. The power input for the
high coolant temperature warning lamp is supplied by the instrument pack via fuse 27. The ECM controls the earth
path to illuminate the high coolant temperature warning lamp.

The ECM illuminates the LED when it detects the engine coolant has exceeded a temperature of 121 °C (250 °F) and
switches it off when the coolant temperature drops below 118 °C (244 °F). The ECM also illuminates the high engine
coolant temperature warning lamp when it detects the PWM duty cycle to the temperature gauge is out of range. If it
is greater than 94% duty cycle when the engine is hot, or less than 8% duty cycle when the engine is cold, the engine
coolant temperature gauge pointer will indicate cold, thus alerting the driver with an additional visible warning.

The PWM duty cycle thresholds for illuminating and extinguishing the warning lamp are given in the table below.
Market Lamp on Lamp off
Diesel - all markets 78.8 ± 2% 76.8 ± 2%

Good luck !

The temp gauge working normally after a rest suggests the coolant was overheating, but never dismiss the possibility of a simple temporary loss of electrical connection to the sensor.

But he says the "rest" was only a few minutes .... when restarted everything was normal ... "coolant" takes more than a few minutes to cool down if it's that hot ... no ?

Red light on = 121 dec C

It might drop 3 deg in a few minutes to make the red LED go out, but the temp guage would still be pegged after a few minutes ... not normal at 50/50,

My money's on an elec' fault ...