There is no perfect ph of coolant. Coolant comes in the bottle with a basic ph. They do this so that it can deal with the acidity produced by electro corrosion etc. As long as your ph is below 7ish you should be fine. I think that the Zerex G05 recommended for german automobiles since way back (they just started using this stuff in the us cars in 00) has a ph of about 5 when mixed 50-50.

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