when I 1st built my 400/512 I had the block hot tanked & then I flushed the cooling passages out with the freeze plugs out, put it all together , 1st test drive all was good, 185ish temp, then it started running hot, turns out that my new Champion 4 row radiator got plugged up from rusty scale breaking loose , replaced the radiator with a ECP 2 row & installed an Gano screen in the upper hose, at 1st it caught a lot of metal scale & I would clean it out when I did an oil change, now when I check the screen it stays clean. the 4 row Champion had very small tubes, a small chunk would plug the tube.