Overheating 95 Merv Villager. had to replace radiator, and has been overheating since. I bled the air out of cooling system, and the heater blew hot air again. overheating continued, esp at freeway speeds. Next I replaced the Thermostat, refilled system and bled air again. Heater blew hot air, though still overheating. Now heater is blowing cold again. not sure what else it could be.

SOURCE: heater blowing cold air

squeeze the hoses to get any air bubbles out and refill coolant as necesary. are you sure you put thermostat in the right way? may be backwards. also may be your sensor.

SOURCE: '90 Subaru Legacy overheating....

cool air and overheating point to low coolant level. Do you have a bleeder valve near the thermostat? You may have air trapped in the system. If no air trapped, the radiator may be plugged up not allowing proper circulation of coolant.

SOURCE: running hot 1996 cavalier

please try a simple test for me. no.1: remove the radiator cap off the radiator. no.2: if you could see the see the radiator opening from within you car much better, then try to crank your car to an idle. if coolant blows out of the mouth of the radiator like an erupting volacano, then take note of this. no.3: while the engine is running at idle try to look at the coolant through the mouth of the radiator, if you see bubbles like washing your hands with soap and the suds trailing to a drain, then take note of this.

the reason why i'm telling you all of this is that, the coolant should flow like a clear stream. you don't have to worry about purging the system of air because, the water pump is already situated a few inches below the highest water capacity of the radiator. it means that if you drained your system and refiled the radiator to the brim, just start your engine and add a few more coolant to fill it up because the running engine simply purges the waterpump of air.

now, if you tried no.2, and you did see and somewhat like an errupting volcano, that means your engine is in serious trouble, so is no.3. however, a tolerable bubble flow is still possible but your valve clearances should be tuned if this happens. excessive bubbles accompanied by blow out of coolant means your combustion gases are seeping through the head gasket due to a damaged head gasket, warped cyclinder head, cracked cylinder head, or even a cracked cyclinder liner(or bore where the piston glides up and down). think back! did you ever experienced overheating you car to a point where it stalled completely? then, you need a thourough engine checkup.

SOURCE: My 97 BMW Z3 keeps overheating

I too had similar problem when replacing the thermostat on my Z3. My advice is top up with more coolant and check the level.

SOURCE: 1994 Dodge Spirit heater blowing cold but radiator is overheating

1st you need to make sure no air in your system open you radaiator cap and your heater to max and see if air bubles or circulation is going on fill up accordingly otherwise you have blockage in your system or water pump if no circulation ////make sure no bubles all bubles should be gone////look for coolant circulation in your radiator make sure your thermostat is not defective or placed in the right position.