I need to replace the temp sender in the head of my '01 C5 2ltr HDI turbo. So need to drain some of the coolant to do the job. Figured I might as well do a full change. What is a good/suitable coolant to use that does not have to come from Citroen? What is the best way to flush out the system / does it need to be flushed, or will a drain out be enough?