Temperature gauge flips high briefly

I have had an erratic temperature gauge shooting into the red for a few seconds and then back to normal intermittenlt over the last 3 months ...about 5 times so far. However last week engine stalled and on restarting had no issues! Don't have access to Lexia yet to read underlying problem. Wondering if anyone else has experienced this and if replacing the sensor may solve the problem. The sensor seems to measure correctly with a meter and is not erratic!
Thank you.

Rajshah wrote: ↑Mon May 23, 2022 2:24 pm I have had an erratic temperature gauge shooting into the red for a few seconds and then back to normal intermittenlt over the last 3 months ...about 5 times so far. However last week engine stalled and on restarting had no issues! Don't have access to Lexia yet to read underlying problem. Wondering if anyone else has experienced this and if replacing the sensor may solve the problem. The sensor seems to measure correctly with a meter and is not erratic!
Thank you.

Changing the sensor would be relatively painless and a quick way to see it clears the fault.

Check you have sufficient coolant in there (the reservoir) too.

Thanks. Will replace sensor.

Got the sensor today. Wondering if I can swap sensor without draining the system if I am quick or does it gush out? Or is this not advised?
Also, will it definitely need bleeding after that if fluid loss is low?

Rajshah wrote: ↑Sun May 29, 2022 3:45 pm Got the sensor today. Wondering if I can swap sensor without draining the system if I am quick or does it gush out? Or is this not advised?
Also, will it definitely need bleeding after that if fluid loss is low?

It won't gush out, but if the cooling system is unknown, maybe it will be best to drain it into a suitable container. You can re-use it, if it is still good - and not brown, blue or sludgy.


The diesel has a good system for bleeding if you have that extra pipe to the reservoir, it is automatic for only a small fluid loss.

The sensor was faulty. Tested it afterwards to find it had a 6 kohm resistance at ambient falling to about 2 kohm at 60 degrees C which is still correct. But then it suddenly goes open above this temperature in the 70 C area and this would account for the red alert! Taking sensor out without bleeding is fine as loss was only 100 cc apart from the fact that the o ring had slipped out of the old one and so had to remove new sensor and reinsert it losing 250 cc!....but still not bad as was able to collect it all without making a mess! All in all, an easy fix! Thank you for prompt responses.