The scoop under the car is a very good idea. We shall agree to disagree on thermal conductivity.

Today's OAT & HOAT long life coolants should keep the radiator interior spotless. Our product for Mercedes Benz allows a 15 year change interval with sachet in tank.

 

Glyn, I don't disagree with you on the thermal conductivity of the metals. It's more that I guess that it's high enough in both metals that it's not too important in a well designed and manufactured radiator. Thanks for the mention of OAT and HOAT. I will try them out. You know that some V12 XJ owners go as far as putting filters in the top hose to collect the 'sediment.'

 

Having to filter sediment is crazy. If the V12 is a particularly "dirty" engine cooling system wise like the old Chrysler Valiant et al slant six 3.7 litre was. Modern OAT & HOAT coolants will keep it spotless. As a belt and bracers approach maybe give it a change one year apart at first as it cleans up the crud or give the system a very thorough flush with a suitable product followed by plenty of water.

Once clean & stable ~ change coolant the minute it ceases to be clear & bright which should be a very long time.