any idea's on this

It seems since i found this forum my van has been having wobbles

today whilst talking my daughter out in the van, i was about 3 mins down the road and the temp gauge went up to 3, then in a min it went to 6 bars, stayed at 6 for about 30 mins, then the temp gauge was full

i carry on and the Stop light came on, i get out check the engine bay, the water in the res is cool ? ? ?

i sit in the van and drive off and its back down to 6 bars

wait in the car park for about 30 mins for my daughter,...

any idea's on this