Overheated help!?!?

Ok so I brought a lr3 or the l322 I believe, it's a 07 vogue 3.6. Basically it had over heated going about 50mph, turnt it off got it recovered back home. I have just sat out there for a hour revving it and letting it idle even took it for a hard drive round the village at operating temp and hadnt overheated. Just wondering if anyone could point me in the right direction. Also the water in the expansion tank goes once started but if I remove the pressure cap it all appears and without losing any. Any help would be much appreciated!!

Welcome Shaun, for quickest & best advice put this in the Range Rover section and select L322 in the vehicle type.
Sounds horrible problem, but might be really simple.
Good Luck!

Thank you mate ! I hope so to hopefully maybe a sticky thermo fingers crossed !!