Thanks Peter, after considering this. I have been wondering if the issue is how the ECU controlled valves are actually operating the coolant flow. As you say, its a complicated system. Its possible that on the cars with no recorded issues the ECU is operating the valves in the design of the program, but in others the ECU may not be doing this as exactly.. I would think that the cooling system is finely balanced for flow and that the valve operations must be gradual and very controlled.. If this was not happening in some cars and the valves were opening ( or closing ) too quickly/slowly this may increase the risk of thermal shock.
Anyway, just an idea..based on the fact that the new radiators are coming with a ECU flash.
