Car overheats and there is air in cooling systems.

no car make or model mentioned so getting an answer is hit and miss
however what you describe indicates a fan drive problem so if it is electric fan cooled-- check the fans for full blade speed ( weak motor operation) or if viscous fan hub ( fan clutch) replace the viscous hub
it is all about moving air through the radiator when the vehicle speed is slow and the engine rpms are high
if the fan is not doing the job of pulling air through the radiator , the car will overheat
at highway speeds the ram action of the air flow virtually makes a fan useless as there is more than enough air passing through the radiator to cool the water
Im guessing here but I suspect that you have a viscous fan hub

There is air in the cooling system, and you may have a bad head gasket or possibly cracked head. Try parking uphill and filling the system with the car running and warm. If bubbles keep coming up forever, the head will have to come off.

8 Things that Can Cause Your Car to Overheat..
> The coolant level is low.
>You have a leak in the engine cooling system
>The thermostat is bad.
>The water pump is failing
>Your cooling system has trapped air
>The radiator cooling fan is not working properly.
>The radiator core has become clogged.
>You have a blown head gasket.

sounds like a bad thermostat its stuck shut causing overheat and no hot air in the car make sur to bleed air out of cooling system after replacing cooling system

did u bleed the air out of the cooling system? if not dop this procedure and recheck for problems.
The generic method of bleeding air from the cooling system is to use a floor jack and raise the front of the car as high as poss, then fill the coolant recovery tank full and run the engine until it just starts to overheat, high end of normal zone on gauge, then shut the engine down and run cold water over the radiator core, this will self bleed the system and the coolant will be pulled from the recovery tank, repeat as necessary, never let the recovery tank run dry or more air will be pulled into the cooling systeml , if it still overheats then you need to have the head gaskets checked with a gas analyzer for hydrocarbons present in the radiator or recovery tank

you have air trapped in the cooling system, do the following procedure to purge the air out.
The generic method of bleeding air from the cooling system is to use a floor jack and raise the front of the car as high as poss, then fill the coolant recovery tank full and run the engine until it just starts to overheat, high end of normal zone on gauge, then shut the engine down and run cold water over the radiator core, this will self bleed the system and the coolant will be pulled from the recovery tank, repeat as necessary, never let the recovery tank run dry or more air will be pulled into the cooling systeml , if it still overheats then you need to have the head gaskets checked with a gas analyzer for hydrocarbons present in the radiator or recovery tank

The generic method of bleeding air from the cooling system is to use a floor jack and raise the front of the car as high as poss, then fill the coolant recovery tank full and run the engine until it just starts to overheat, high end of normal zone on gauge, then shut the engine down and run cold water over the radiator core, this will self bleed the system and the coolant will be pulled from the recovery tank, repeat as necessary, never let the recovery tank run dry or more air will be pulled into the cooling systeml , if it still overheats then you need to have the head gaskets checked with a gas analyzer for hydrocarbons present in the radiator or recovery tank

You have gone through a lot of trouble so far replacing parts. I wouldn't rely on rad additives for a fix sometimes they do more harm than good. You could just have an air lock in the coolant system. Did you try running the vehicle without the rad cap for awhile to release any air locks that may have occurred? Have you tried a new rad cap? Hopefully this advise helps you some what.

check for any air locks,bleed cooling system,also check cooling fan cutting in,if not check fuse and relay for fan and fan motor,if system is pressurising suspect head gasket blown.