temp problem

[diesel09]

okay so today i fitted my new mid section(straight through)
everythin was fine got it all on started it and sounded realy nice,

anyway i turnd the engine off to make sure all the bolts on the clamps were tightened properly and all the rubbers were on properly,

then when i started the car again, the revs shot up to the limitter and the temp shot up to 100 so i switched the engine off and left it for a second, then started it again and it idled okay but didnt sound no where near as nice,

anyway so ive been tryna figure out what the problem was, and my mate said when the car was just left idling he twisted the water bottle/tank lid to see if it was on properly( i think he was just tryna be a mechanic and wanted to see what would happened if he loosend it)

so now ive left the car to cool,

any ideas?