Ph is the critical factor with MB coolant. A 50/50 coolant and water mix will result in a ph around 7 or neutral. When, and if, the ph reaches 8 it should be replaced ... every 3 years according to the Owner's Manual. Check the ph with a swimming pool ph test strip. High ph coolant causes embrittlement of plastic parts and erodes the internal alloy engine parts.

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Fred Hoelzle