I'm pretty much aware that mixing Orange (Dexcool) and regular green antifreeze is a bad idea.
However, what about the new "universal" extended life formulas that are yellowish in color? They advertise that they can mix with any other antifreeze. The dude at Napa said that they won't mix. Who should I believe?
The NAPA dude doesn't really know. He is saying what he thinks, and what will protect his ass.
I would prefer not to mix the species. I think that some CAN be mixed, but if I am going to change, I am going to flush the block and the radiator, and add all new coolant. It is just a cleaner way to do things.
The only problem with mixing them is that you then have to treat them as the same as a straight green mix. If you take it to a shop after it is mixed they will complain because they can't use the Dex or Green recovery machines without contaminating them. Other than that they will mix just fine.
I found this page recently. It may help.
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