Thanks, both. What I think that we know: 1 There are different types of coolants that fall into a few big families. The colour is sometimes consistent within families but not always, especially with less common products. 2 There will be some variation between products within families, especially in minor constituents such as inhibitors. 3 One supplier of radiators suggests that some leaks have been caused by use of "red" coolant and recommends "blue" coolant. But we have never seen anything resembling a controlled comparison of this. The evidence seems to have come from seeing what type of coolant has been used in radiators that have leaked. 4 Using "blue" coolant in many current Seven engines would be against the recommendation of the engine supplier to use "red" coolant. 5 "Aluminium" radiators might contain some copper or brass components. All corrections and suggestions welcome. Jonathan