let truck cool down. drain radiator. refill with water start and run truck to operating temp shut down let cool and drain rad. do this a few times to where you feel it is as clean as its gonna get. make sure you use the PROPER coolant. dont worry bout the mix as seein you will have only water in the motor. it will mix itself once it gets to operating temp again. pour coolant in strait coolant. let run with rad cap off to help "burp" the system. fill to the "new" max line on res. and be done with it. use water wetter or purple ice. helps alot