So i just replaced the head on my 4.0 with a rebuilt one (valve seals were leaking on the old one) and its running 20+ degrees hotter than it used to before the replacement. I figured it was a thermostat, so i replaced it too. what could be the problem? water pump is recently replaced, new coolant, and im sure i got all the air out of the system. It goes over 210, and settles back around 210 unless running hard down the highway and it creeps up higher.

 

The first thing to do is verify the temp with a heat gun and make sure of you temp. After that do a quick search on this forum and you will find a lot of possible causes for over heating. If you still have a heat problem we can go from there.
Good Luck

 

i just "burped" the system by loosening the temp sensor on the back of the head. i think that helped but i wont know for sure until i run it down the highway.

 

follow the link in my sig.

 

only closed cooling system are affected by burping once thermostat opens fill up and install cap

 

If it didn't start overheating until you replaced the head, then either the head is bad or you did something wrong, like putting the head gasket on wrong.