Coolant Recommendations -620ti

I know that the ti originally came with blue coolant, but a previous owner has changed mine to OAT(pink), is this likely to cause any problems as I would like to change the coolant when the car is back from it's respray this weekend and I know you can't mix them?



I would really like to return to blue as there is some talk of OAT rotting rubber hoses and seals on the 75 forum, but how difficult is it to complete remove every last trace of the OAT?



What is the correct method for completely draining every last drop from the system, or should I just drain as much as I can and use PRESTONE which is supposedly kinder to the car than OAT but can be mixed with either?

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