Sorry its took so long as been trying a few more thermostats and i think i've just cracked it managed to get hold of a WAXSTAT one the other week and just got round to fitting and trying it and just been on a long motorway run today with heater on full blast the whole 60 mile round trip just to see what it does and the heater never missed a beat, the gauge still fluctuates when say coming off at a junction but only slightly and nothing like it was so i'm well chuffed 😁