I have a 1988 jeep cherokee laredo 5 spd 4x4. So like the title says whenever I crank it over it idles completely fine then I look at the temp gauge and it'll slowly creeps to 210 and if I turn on the defroster it turns on the electrical fan and my volt gauge drops below the line in between 9 and 14 but if I don't put on my defroster it will go past 210 and overheat and pop the overflow tank cap off and spew out my anti-freeze can someone tell me what I need to replace because I've replace the thermostat already.

 

Replace the bottle cap with a Napa part number 703-1396 for starters.