Hi all got a leak somewhere in my coolant and I was suggested that a put radweld in it as it has worked for them. Does this damage the engine at all and if you have a reservoir for the coolant in the car do you put it in there so it can go round the system??

Dont do it!. If anything, all it will do is restrict flow. You would be far better off locating the leak. It should be obvious where it is leaking as you will have a build up of dried coolant somewhere on the engine. Try checking the thermostat housing as that is a favourity aas will as the coolant piping and the rad itself. If there are no leaks it would suggest you may have a slight leak in the head gasket, but that is worse case scenario and probably unlikely.

It may also be worth changing the expansion tank cap as if its not sealing properly the coolant boils at a lower temperature.