Thankyou very much for an indepth informative reply. I did (2 days ago) add approx 300mm of the red carplan OAT coolant purely as a top up, do you think it was safe to do this and that nothing bad will happpen regarding damage to the engine as a result, this is assuming that their was a different type of coolant already in the system? I am going to book the car in for a flush and coolant change so i know exactly what is in there, but have i done anything wrong or compromised the engine in any way at all in the meantime? (i have driven 50 miles since adding the 300mm of red carplan, it has been very hot the past 2 days and occasionaly the temp guage did creep just past the half way point in the 'normal' zone when in slow traffic and stay just past half way for quite some time, (it never did go to red or near to red) is this ok or is their any reason for concern?) i hope i have not reduced the cooling in the engine which may cause problems in the future...