I have wondered too about the positioning in the circuit of the temperature sensor for the gauge and the thermostat. I wondered if the stat is controlling the temperature as normal and the gauge is sensing the outlet temperature from the engine - BUT, I've renewed the stat on mine to make sure it is working OK (made no difference so I assume the one I took out was fine) and it is as you would expect a standard fitment SO in a normal saloon car it would only be on very rare occasions you would see the temperature gauge move let alone rise significantly no matter what speed. The rad I have is a Mulfab one (I fitted it because the standard one developed a leak, replaced it with a standard one and that one didn't last long either so I thought the Mulfab one would kill two stones with one bird). That being the case it is larger and so if the air flow is OK why would the coolant temperature vafry depending on the speed other than the speed itself causing an air flow restriction. I don't understand why this should be as there are plenty of louvres but it is. We'll see what happens.
The way I understand it, aluminium radiators provide more cooling, due to the fact aluminium is an efficient heat rejection. Hence the reason the fan does less work
Copper is a much better transmitter of heat than aluminium which is why I asked earlier if the later radiator cores were copper or aluminium.
My original Zetec rad was copper I think but because my new ally rad is bigger and has more fins it does a very good job.
Copper has almost double the thermal conductivity of aluminium.
Simon of Sifab is the expert though so I will stand by to be corrected.
