Temp gauge cutting out

[3-Max]

Having changed the coolant, doing an engine flush, replacing the radiator drain valve assembly & a hose (& fixing leaky crabs) I ran the engine for a while to get everything upto temp to check for leaks etc.
I noticed that occasionally the temp gauge would flutter or just drop straight to 'cold' then after a few seconds spring back to life. I don't know if it was just coincidence but it seemed to cut off most often right after giving the engine a quick blat.

Thoughts pls.

 

[MaxMidnight]

I know I'm stating the bleedin' obvious but you are loosing power or coolant temperature feed to the temp indicator.
Check the connections to the sender as you have been in that area and check you have the earth wire connected.
If they are OK then check you have power to the temp indicator.
The 'blatting' of the engine is probably causing a connection to vibrate and loose continuity.

 

[3-Max]

I know I'm stating the bleedin' obvious but...

There are people in the world, such as myself, for whom the bleedin' obvious is anything but (& it's a royal pain in the bum). So believe me, it's much appreciated when someone does just that. Thanks.