You should run a 50/50 mixture.

You can actually buy a bottle a coolant that is already mixed 50/50 with water at your local parts supply store.

Otherwise, I believe it is always better to run a higher percentage of water to coolant, i.e. add water not coolant.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".