There is only a few components that can cause the vehicle engine to overheat. I will list some components and there purpose.
Reservoir pressure cap: This serves two purposes, one to maintain cooling system pressure (about 16lbs of pressure at operating temperature) and second, cause a vacuum to within the system to suck more coolant from the reservoir into the cooling system or press to push out coolant from the cooling system into the reservoir.
Thermostat: Regulates cooling system operating temperature by opening and closing a valve to prevent coolant flow throughout the cooling system.
Water pump: Pumps coolant through the cooling system (when the thermostat opens) creates flow and is always pumping or cycling coolant.
Heat exchangers or more commonly radiator or heater core: These give off heat to the air that goes through the radiator or heater core.
Coolant: a 50/50 mix of coolant and water is required. If you have just straight concentrated coolant it can cause heat exchange issues because water retains heat so much better and releases it.
If you replaced the thermostat and added a 50/50 ratio of coolant and water (or 70/40 of coolant and water if you live in cold climate such at Alaska) and there is no air in the cooling system. Then the only other issues could be the water pump is not pumping coolant or the air fins on the radiator are restricted or the radiator is restricted or the cooling fans are no coming on.
Worst case could be a blown head gasket or cracked cylinder head or engine block pushing exhaust gases into the cooling system causing overheating while over pressurizing the cooling system usually forcing coolant out of the reservoir.
I hope this helps. When does the overheating occur? At freeway speed or around town or idling in stop & go traffic?
Monday, October 7th, 2013 AT 8:13 PM