My friend’s 04 Sebring (6cyl) is overheating. After start up, almost immediately the water bubbles in the radiator and heat builds. He has replaced the radiator, thermostat, water pump, and even rebuilt the heads - still the overheating issue. Any ideas on what may be the problem and how to correct? Thanks!
Is the electric fan turning on as it should? Has the cooling system been purged of air?
Define “rebuilt the heads”. Replaced the head gaskets? Rebuilt valve train? What is the compression on each cylinder?
Was the head taken to a machine shop for testing against cracks? Some of them can be very hard to find. If there’s a crack, forcing air into the water jacket, then there may still be a problem with the heads.