Do you know where the coolant is going? Is it coming out or being consumed? There is a block check tool that can be purchased at NAPA. It checks for hydrocarbons in the coolant. You open the coolant tank and put on the tool that has a chemical in it. As the engine heats up you pull air through it and if the blue chemical turns yellow, it has a combustion leak into the coolant. Where? That has to be determined.

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