Hi, welcome to JA.
Are the fans comming on? Is the check engine lamp comming on as well?
Thanks, XXXXX XXXXX you may need to get a block test done on the cooling system. This test will check for engine combustion gases in the cooling system and this will tell us if the head gasket is failing. Or you may have air trapped in the cooling system - have you already tried bleeding the system?
There should be an airbleed on the radiator, but if you new one is aftermarket...it may not. What I like to do is (on a cold engine) pull one of the hear hoses and fill the radiator/resevoir until coolant runs consistant from the removed hose. When it does, reinstall the hose...fill the system...than let the engine run until it is at normal operating temperature on the guage...shut it down, and let it cool completely with the cap still off. This helps purge the air out, I like to leave troublesome ones open all nite. Than add any remaining coolant to the resevoir if air purged. Cap it off and let it run, monitor the fans to come on at normal temp, if the thing still overheats, you should get a block test kit and see if the head gasket is an issue.
I'm sorry I forgot to leave a pic of the heater hoses i'm talking about (see below)....also be sure your careful and take the hose off gently, you don't want to break the heater core.