Need help Nissan xterra

[Shannonkeith]

I have 2000 Nissan Xterra it ran hot cracked a head we changed the head still ran hot then put block seal in it then it don't run hot while idoling but when u drive it about a half mile it runs hot then when u let offf gas it cools again

 

[kanewolf]

Water pump, timing wrong, clogged water passages in radiator, bad sensor, thermostat, .... Lots of reasons. There was a root cause that wasn't found when it ran hot before the new head. You will have to do more detective work. Look at radiator hoses with an infrared thermometer. Look at the spark plug area the same way. Are all the cylinders equally hot?