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Possibly leaking head gasket. Easiest way to check would be to fill radiator full, start engine and watch coolant level in the radiator cap opening. The top radiator hose will become hot when thermostat begins to allow coolant flow through the radiator. You may have to top off the coolant. Still with the radiator cap off watch for water belching out of the radiator neck. If coolant does belch out of the radiator cap neck, refill with water. If it belches out coolant again it would be combustion gassed forcing the coolant out of the radiator.
This process should take about 1/2 hour to diagnose if it is a head gasket leaking combustion gasses into the coolant.
The radiator fan may run once car is shut off to cool engine compartment to prevent gasoline in fuel lines from vaporizing which would cause a condition called "vapor lock". A car won't start if fuel lines are vapor locked.
Good luck, I hope this helps you to figure out the problem.
Change the thermostat if you did not change it already. When the engine gets hot it usually ruins the thermostat. Check the fan and make sure it is turning this is also controlled by a thermostatic sensor that can also go bad when the engine gets hot. Try pressure washing the radiator through the grill and from inside the engine compartment. It may be plugged with bugs. The electric fan is controlled by a temp sensor for startup and shut off. You could have a gasket leak into the combustion chamber without getting coolant in the oil, or oil in the coolant. Remove the radiator cap and look for bubbles coming from the bottom of the radiator when engine is running. When you put coolant in listen to how it sounds. It should gurgle when filling. This is the trapped air escaping from the engine and bottom of radiator. Much like an upside down soda bottle when pouring a drink. Good luck get back to me if you still have problems. And let me know if this solves it..
The cooling fan isn't causing the engine to run hot, it's electrical and cannot heat an engine. It is turning on in response to your engine running hot. Check coolant level and age, if it's still running hot then check the thermostat - it could be stuck closed. If the thermostat is fine and coolant level is full, it could be partially clogged radiator or head gasket problem (a sure sign of bad head gasket is that your coolant keeps disappearing with no leaks).
With blower on high and tempature to max heat check to see if you have good air flow in all mode selections (defrost, vent, floor etc.). If so and you still have no heat then check heater core hose going from engine to inside car to heater core with vehicle running and coolant tempature about half on guage. If both hoses are hot and coolant in radiator/overflow bottle is full then hot cold blend door is stuck in cold position. If coolant level is low you will get no heat, check coolant level first.
Most cars have an 2 electric fans on the radiator. One will run when the coolant gets hot and the other will run when there is more cooling demand OR it will run when the AC is turned on. My guess is, the second fan is not running when your AC is. Your AC system creates heat of its own. The heat is removed through the condenser (radiator-like coil) which is usually located in front of your engine radiator. Without a fan the heat is transferred into your engine radiator causing it to over heat. This would explain why it overheats while idlling and not while driving. While driving, air is flowing through the radiator and condenser. to provide the necessary cooling. In short, check to see if both fans are running when the engine is hot and the AC is turned on.
Make sure the engine is not hot and open up the radiator cap.
Turn on the car and let it idle with the cap off.
Allow the car to warm up.
When the engine is hot and it is getting close to overheating, look down into the radiator. The coolant should flow. (It should look like a little river is going past the radiator opening). If the coolant appears to be still then your water pump is bad.
Yes, could have air traped in the system, but from my experience this only gives a false indicator of being hot. When I see a car overheat I think thermosat,fan, radiator cap, or headgasket/craked head in that order. You have already changed the thermostat, so the nest thing to check would be the fan clutch. You can check this by spinning the fan when both hot and cold. When hot it should get very hard to spin- I like less than one revolution when given a good spin.Also a good indicator of a bad fan would be if it gets hotter in town than on the highway. On th e highway you get ram air that helps to cool it down. Radiator caps need the gaskets inspected for crackes and hardness. If crackes are present or to hard they won't seal causing the radiator to overflow. They should also be preasure tested by a local shop or parts store. If the preasure is to low this will also alow the car to heat up quicker and also allow the radiator to empty at a lower temp. The best way to test for a cobustion chamber leak is at a shop. Many shops can test for this right at the radiator with a special dye that will change color in the presence of combustion chamber gases in the collant system. You will notice that I never metioned water pump even though you already change it. Water pumps either pump or they leak, very rarley will they not pump water causing an overheating problem. The only way they will cause an engine to overheat is if they loose the ability to pump water through the loss of the impeller or a broken shaft- or on the very rare occasion an impeller that has run so long that it is worn out.
No heat is often a symptom of low coolant, usually followed by overheat. There are other controls that regulate heater, but right now, re-fill the cooling system with engine running and heater on high, then check for leaks (coolant you lost went somewhere...you need to determine where) Low coolant will damage your engine. Take care of that first, then if heater still does not work, then do diagnosis on that. (if you loose the engine heat won't matter, will it!)
The water (coolant) in the expansion tank will rise and fall with the engine temperature. What the expansion tank does is collect and return coolant to and from the engine. When the engine warms up the coolant gets hot, builds up pressure and opens up the radiator cap. The coolant then goes into the expansion tank. Now when the engine cools down the pressure drops in the cooling system and the pressure drop (vacuum) pulls the coolant back into the engine via the radiator cap. The radiator cap allows the cooling system to build up pressure and by doing so increases the boiling point of the coolant, but when that pressure exceeds the caps rating the cap opens and the coolant goes to the expansion valve. The cap has another part to it that when the engine cools down and a partial vacuum is created in the cooling system a "valve" in the radiator cap opens and allows the coolant to be drawn back into the engine. I would look at your radiator cap to see if any gunk or build up is on it, and check the rubber gaskets for cracks. It's easiest just to replace the cap because they are inexpensive and easy to replace (2-10 dollars). The expansion tank should have two hoses on it. The one on the bottom comes from the radiator and the one on the top (possibly part of filler cap) runs down and is open to the ground. That way if it is overfilled or becomes overfilled it will slowly leak onto the ground. When and if you change your radiator cap, make sure the engine is cooled down, remove cap and start engine and turn heater to full blast, full heat. Leave the cap off and let it run until engine warmed up. This should burp out any air pockets that may have happened when coolant was changed. Also top off the coolant in the radiator while it is running. Hope this helps and good luck