Temp gauge drops on rev

Car was driving well when I noticed the temp gauge at on the bottom. When idling the temp gauge is fine but as soon as I rev it drops to zero. I was initially thinking electrical fault? But read a few things about the temp sensor.

Needing the car tomorrow - would it be safe to drive - i.e. Will the fans still kick in if required? Up until now the temp has been solid but don't want to run the risk of damage .

Thanks in advance

Probably an earth fault.
The temp gauge is fed from a separate sensor. The ecu controls the fan from a second sensor so the fans should still operate correctly. :broon:

Any quick movement of the temp gauge is usually an electrical problem.
It moves pretty slowly in response to a rise in temperature, unless there is an air bubble stuck near the sensor, when you can get rapid fluctuations.Usually from normal to 3/4 and back rather than 0.

Had exactly the same last Friday night. Had just got onto the A75 when the temp gauge dropped to zero. Stopped immediately and switched off. Checked the expansion tank etc, and all seemed well. Started Roxy and the gauge registered as normal, accelerated and the needle dropped to zero.
As I was nearly 3 hours from home I pressed on. (How many levels of paranoia are there?)
Got home and spent Saturday morning checking. All was well behind the instrument cluster, so took off the engine cover and checked the temperature gauge sender. (The blue one underneath the pipe.) It had been held on with a zip tie that had broken, allowing the connector plug to work loose and make intermittent contact. Pushed it back on and zip tied it in place. All functions back and having done 300 miles since, all seems well.
Hope your fix is as easy.
Winko

Winko wrote: Had exactly the same last Friday night. Had just got onto the A75 when the temp gauge dropped to zero. Stopped immediately and switched off. Checked the expansion tank etc, and all seemed well. Started Roxy and the gauge registered as normal, accelerated and the needle dropped to zero.
As I was nearly 3 hours from home I pressed on. (How many levels of paranoia are there?)
Got home and spent Saturday morning checking. All was well behind the instrument cluster, so took off the engine cover and checked the temperature gauge sender. (The blue one underneath the pipe.) It had been held on with a zip tie that had broken, allowing the connector plug to work loose and make intermittent contact. Pushed it back on and zip tied it in place. All functions back and having done 300 miles since, all seems well.
Hope your fix is as easy.
Winko

Can you get to it from the boot hatch? Don't have much time tonight to dismantle and was hoping to use the tomorrow am!! Typical!!

Can't get at it from the boot, you need to take the inspection cover off.

Finally got to look at this tonight - are there any checks I can do to rule this out? Where is the best place to purchase a new sensor. I went across the plug on ohms and it seemed to kick the fan in... any type I need?

Yes that's the coolant sensor that controls the fans.
The gauge coolant sensor is underneath that one.

Thanks - think I have bought the wrong one then - or are they both the same?

Tiger78 wrote: Thanks - think I have bought the wrong one then - or are they both the same?

No, they are different and give false readings if used in the wrong location.

IIRC the blue one only has 1 lead.

Further more MEMS 1.9 and MEMS 2.0 cars use a blue sender for the gauge and a brown one for the ECU while MEMS 3 cars use blue for the gauge and black for the ECU, black, brown and blue are all incompatible with each other.

Thanks for the help - found the coolant sensor with no wire on - found the wire and plugged in and i now have temp on the inst cluster....happy man!!

Really glad it's sorted. Exactly the same result as I had. Keep smiling!