Temperatures gauge appears low

[Smithy860]

I noticed last few days that the gauge on the dash gets to 60 and then can suddenly drop to 40 then back up to 60 in the space of 5 seconds.
I guess I should change the stat and go from their. Just wondered why the gauge would do that ?

 

[OneForTheRoad]

its normally caused by the rushing wind hitting the radiator cooling it down when youre doing 60/70 mph . a properly working stat wont open till 90 . so you are less likely to see a falling temp gauge.

unsure about the 5 seconds thing , you maybe need a real time scanner plugging in to see what the temperature actually is in real time .