Happy New year Alibro and all members of this forum, my thermostat stayed open as they like to do during the winter when you need it to work so I did your Renault 5 fix and stuffed it up the tube with the help of a smear of vaseline. Thank you all for this valuable tip, the temp was up to normal within miniutes of fitting, now runs at 88 - 92 degrees and i don't have to wear 3 jumpers, 1 balaclava and a pair of gloves to go for a drive.
Warm regards
Paul ps I forgot to mention that my friend, an 80+ year old mechanic, suggested that I drill a 1mm hole through the body to allow a little water to pass otherwise it will take longer for the thermostat to work. He maintains that it takes some time for the heat to move from the engine, up the tube to the thermostat, the small hole allows a flow of water that brings the hot water up to the thermostat a lot quicker. What do you all think?