Temp issues with my Turbo 2H

[FJ turbo 75]

Just got home from a run on the Hyway and while comming through the burbs the temp guage is jumping up to just under the hot marks , then drops again shortly after .
( Normal round town running it runs approx quater on the guage and when on the hyway at approx 110 klm or 2250rpm it will sit at approx just below half and Turbo is an AXT .
Upon checking the radiator while still warm once home it doesn't have any pressure at the cap AT ALL !!!! which alarms me greatly , but is still full to the brim with good clean water with plenty of inhibiter (green).
So i'mm thinking the thermastat is mabey dodgy and am obviosley hoping it hasn't got a head problem.
Have spocken to the previos owner and he said it has done this temp spike thing before but always no problem after .
So please tell me what your ideas are so i can mabey fix this prob quickly as its my work truck plus is going to be doing quite a few hyway clicks in the next couple of months.
Yes it has got the standard overflow bottle and is sitting at the level it always do's

[Sixty's Guy]

Maybe get yourself a VDO temp gauge and sender, just to be sure. I don't trust my temp gauge.

[sambo]

sounds like a sticky thermostat.

[cruiser60series]

sounds like a sticky thermostat.

I've not heard of this but that sounds exactly like what would happen if there was a sticky thermostat.