The Dmax does not need a coolant additive to maintain ph in the system. Just keep the coolant clean and change it on a regular basis (I like a 50000 mile interval even though 100000 is recommended). The coolant additive package has the elements needed to protect the aluminum and steel components (and brass) in the system. The best thing you can do when changing out the coolant is to use de-ionized water from a jug. the purity will help keep things clean in the engine.
Ford's need to pay closer attention to the ph in their coolant system. Wild variations in ph cause the protective corrosion layer on the water walls to break down making the Ford block suceptable to cavitation pitting (from weak cylinder walls). After enough of this cavitation pitting, small holes will develop in the cyinder walls and a coolant leak will develop.
Be carefull with the water wetter. It breaks the surface tension of the coolant to allow better thermal transfer. Just be carefull that the additive doesn't interfere with the additive package of the coolant you choose (Dexcool). I don't know how it wouold react with it, if it would at all. My advice, just stick with the regular coolant. Just keep it clean.
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