He has bought a TR7 circular water plastic expansion bottle that is fitted with a radiator cap. This bottle has an inlet towards the bottom of its body that is connected to the radiator overflow tube underneath the rad. filler neck, he has used fuel pipe and attached the pipe using fuel pipes clips, this pipe will be pressurised hence the need for secure fittings. All one then does is fit the old rad cap to the top of the expansion tank, the old overflow pipe to the overflow outlet on the rad cap fitting and a rocker cover oil filler cap onto the radiator. The joy of this is as it sealed water should be siphoned back and forward as Triumph originally wanted, but never happens as the old overflow bottle never seals correctly.
Keith tells me it does work and increases the amount of coolant available. Robsport sell secondhand bottles at a tenner, so the total cost of the mod should be £20ish including pipe and fittings. I have ordered 2 bottles and will be doing this to the GT6 and the saloon. The price of new bottles is £40 or so, obviously cheaper to go for secondhand items. Only snag with this is that a bit of TR7 will be fitted to the car!!!!!
Thanks, Mr Dandridge!