defender temp gauge help needed

[Bigbird]

Hey all hope you all had a great weeekend,i did ,took my dogs for a swim with the misses and then watch a couple of young blokes bog there 4runner just where i had driven!!!!,they were bogged big time,i watched them for about half an hour until they made things worse.
i went over and said i can pull you guys out if you like as i have no choice as they were bogged in the middle of the track,i pulled them out then continued on my way home,Go THE LANDYS!!
Anyway guys i have a slight issue with my temp gauge i replaced every single hose (radiator hoses the lot)even the little one with the tpiece from radiator to header tank that was $75 on its own!!anyway since i changed all the hoses everthing has been all good until i had to fit a new top (thermostat to water pump) hose that i had to order i didnt lose much water when i changed it,but now when the engine is cold the temp gauge goes from cold to half, back and forth like a yoyo whats the go,i does this for the first 5 minutes of start up,then she just sits on halfway like normal,any ideas...oh 97 110 300tdi trayback......cheers wes

[hook]

Have you checked the wire at the sender unit, you may have knocked it?

[isuzu110]

Air pocket in the cooling system ? Problem with the earth on the temp gauge ?

[Blknight.aus]

that'd be the thermostat cycling.

[Freestyler]

Did the new termostat have a hole in it? Did you put it to the top? If it dosen't drill about a 6mm hole in the top, this allows water flow past the termostat and making it work properly, it also lets out any air trapped. When you refill a radiator after working on it, it is good practice to run the engine at about 2000rpm for a few minutes while topping up the radiator, also turn the heater on. The speed of the water at these revs should drag out any air with the water into the radiator.Tim