okay so I got my car back from the garage and its now a completely different car!
Gaz you were right about the temp sender dying, it also had a faulty fuel pump which was why it was jerking when i tried to boot it, and the stupid owner before whacked the boost right up so was over boosting which is now all sorted.
The garage also change the spark plugs (just cos they didnt look fresh) and fixed a small oil leak and the reverse light switch on the gearbox died.
Oh and I also fitted my LED dash conversion!
Didn't take too much effort, just taking the dial surround out and swapping the bulbs over, none of this soldering nonsense!
Befores:
(when I took the unit apart, there wasn't even a bulb in the left socket!)
Afters:
Much better! Need to clean the dial cover though, looks a bit misted up in the photo's haha