What kind of coolant is ok to run in these 6. 7 engines? If there is another kind will it mix with the stuff that's already in there?

What kind of coolant is ok to run in these 6. 7 engines? If there is another kind will it mix with the stuff that's already in there?![]()
You have a 6. 7? Share your thoughts with us... would like to get a new truck, but with some of what I've been reading here, I just don't know.![]()