Why does my 2000 malibu over heat i repcled thermostat .waterpump,fans. radiator does notleak plus cold air comes out when tempature gage is on heat we tried bleeding lines, also sounds like agurgling sound when making a left turn, replaced heat sensor ,drive it a mile and it overheats.

A true overheat is when the coolant is bubbling back into the coolant recovery tank. #1 radiator cap not holding pressure #2 stuck thermostat #3 restricted air flow #4 bad fan clutch #5 bad waterpump #6 restricted water flow in radiator #7 blown head gaskets this is the end results to a overheated engine .

Can you check/feel along your hoses from the engine towards the radiator when hot. It should obviously be uniformly hot, Suddenly going cold would indicate a blockage. Same check through the radiator and back to the engine, obviously it will cool through the rad but if it goes stone cold after the rad then that still indicates a blockage which coupled to the over heating is a prime suspect. If you've lost any water then it could be air locked and need properly bleeding. Jon

Hi, Yes you have an air lock in your system, you may get this sorted by 1/. Removing one of the cooling hoses & try to blow with air.
2/. Drain all the system then put your heater on inside the vehicle & have the engine running & refill the system Start to do this from a cold engine. Please leave me feed back: Malcolm Campbell, Thanks.

Your radiator cooling fan will only come on when the engine temp has reached the point where it needs to have air forced through the radiator and thus bring engine heat back down to safe operating range. If your heater is not working check to make sure the fresh air vents aren't stuck open (are the controls stiff or not going all the way across?) check also that the heater shutoff valve lever which is usually situated on the firewall at the rear of the engine and can be found easily by tracing the hoses back from the thermostat housing aren't bent and/or seized up.

Wait till the engine is cold, remove the radiator cap, start engine and look for coolant gushing out of radiator or a lot of bubbles, its possible you have a blown head gasket.

If it where your water pump isthe vehicle would overheat. After you replaced the thermostat do you run the engine at idle with the radiator cap removed until the radiator fan came one? This will help push the air out of the system. There are two other possibilities. 1. The heater core is plugged. Back flushing the heater core may help remove the built up debris and get you heat again. 2. The blend door may not be fully transitioning from cold to hot. You should be ale to hear a district change in how the air sounds when switching from full hot to full cold. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Check the waterpump and thermostat. When the waterpump doesn't turn, engine heat is not transported to the radiator. When the thermostat doesn't open once warm the same happens - no engine cooling.

The radiator should be hot op top and cooler at the bottom. If it's cold allover then there's no cooling fluid transport

with winter being here you might want to consider having a new thermostat put in to increase the heat in side,but make sure your radiator is full when engine is cold

If it is a regular fan, check the fan clutch. If it is an electric fan, make sure it is coming on. Other than that you might be sure the AC condenser that sits in front of the radiator is not plugged up with grass, bugs, etc...

Check or have the electric cooling fan or fans checked, to see if they are coming on, and the radiator cap checked. You've done everything else.