On my old F350 Diesel with the 7.3 Navistar engine, I have test strips that I use to test the coolant for certain parameters. This is important because if it's not correct it can cause cavitation of the fluid which can wear through the cylinder walls. There is an additive you can add but only twice per Ford before you need a complete replacement of all the fluid. All the backyard mechanics say flush it with the hose! Like Karl said DO NOT! Only distilled water and you don't have enough!! I just gave a way a 2003 Tahoe with 335k miles, burns a little oil but still working good!