Antifreeze: Red or Green?
While it is ethylene glycol based antifreeze, the concern with mixing comes from the fact that there are very different chemical inhibitor packages in use. Most leading technologies will work very well when used as intended, typically at 50% in good quality water. If the coolants become mixed with Dexcool®, however, one study showed a possible aluminum corrosion problem in certain situations. The other question is a concern for dilution of the protection packages. At what mix is the there too little of either inhibitor to protect the engine? As a precaution, both GM and Caterpillar instruct that contaminated systems must be maintained as if they contained only conventional coolant.
I would not recommend using Dexcool® in a vehicle that did not come from the factory with Dexcool® in the cooling system. It would be very difficult, if not impossible, to flush out all the conventional anti-freeze coolant from the cooling system of an older vehicle, and any conventional anti-freeze would contaminate the Dexcool®.
Compared to old-fashioned phosphated antifreeze, Dexcool® may be more stable and improve water pump life. Evaluations of the two technologies to compare their respective service lives have found them comparable. In fact, a Ford Motor Company study concluded that organic acid coolants do not offer any significant advantages for the consumer over current North American coolants. In a modern car with a well-maintained cooling system, current North American and OEM factory fill coolant corrosion protection can be extended far beyond previous expectations.
So the bottom line is this, if your car came from the factory with Dexcool®, use Dexcool® for replacement or to top off. If your car came from the factory with standard "green" antifreeze, use that for replacement or to toping off. Case in point, Dexcool® has been known to cause head gasket and water pump failure on some Ford OHC V-8's.
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