| Being on the wrong end of cooling system issues myself, I highly recommend the BMW coolant. Regardless of color like billb suggests. If there is a blue and white propeller on the bottle, I'm using it.
As for the blue coolant turning green, unless corosion in the system is yellow, then you had green (or yellow) stuff in your engine when you did the rad swap. I used nearly 10 gallons of distilled water to flush mine last year.
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