I am a new powerstroke owner, I just bought a 99F350 with the 7.3. It has 280k on it but I got a good deal. The coolant looks old and slightly dirty so I would like to flush it. On my old cars I used to drain the cooling system then circulate water in the system then drain it again. I read something about a special antifreeze additive for the 7.3 that prevents cavitation. Is a 50/50 mix recommended? Any input appreciated!