Gaskets or hole
 

The other night my Mrs was out in the scoob when the temp gauge went up. Luckily she noticeed and pulled over when I got there it was out of fluid.I topped up drove it home a mile nice and easy no dramas apart from no heat coming from the vents although I did get warm breafly. Next day I topped up fluids and ran the car up to temp left the lid off the expansion tank 20 mins fine yet still no heat from vents. Took it up the road hit boost temp went up to 3/4 and a little heat from vents but as soon as I stopped to turn round temp went down and vents went cold.I got home had a look about and took the cap off again but there was no pressure even tho it was hot,both top and bottom rad hose was warm.
to say I'm confused at the mo is an understatement as ive had 2 garages on my facebook say head gasket and a mate who builds his own big hp scoobs say he thinks it's got a leak but can't come look yet. Has anyone else had this problem before any advice ect.
Tia steve

A water leak from the hoses or rad is first thing to try, if it's an internal leak, it usually is head gaskets on these engines.