pulled the top of the engine to bits to have a poke around (more later).
Anyhoo, found a strange looking thermostat in there.
Never been into it before and had bought a new one in case it failed the pan of water test.
new one on the left
They both opened at the same rate (180) although the bigger one made creaking noises as the mechanism expanded !?
It was slower to open and you could see scratches on the shaft thing.
I peered into the manifold I could see where the old one had extended so much that it
had been hitting the bottom and had very clear marks thru the discoloured metal base.
Dunno how much it was prevented from fully opening but may be part of a general running hot bug.
It's obviously a high tec bit of kit but not suited to a Performer manifold!