Just had water pump installed in 2001 impala, still overheating. Hoses are collapsing. Is this the thermostat? If I just replaced the thermostat, hoses, sensors, radiator cap last year, what could this be?

Air pocket stuck near cooling fan switch. Look for a brass flat headed screw near the upper radiator hose. Crack it open slightly while the engine is running and at operating temperature. It'll bubble a bit. Close it when only coolant streams out of the hole (gently, it's brass so it can break easily).

Overheating is caused by:
1. plugged radiator core
2. Wrong mix of water and coolant.
3. Low coolant level.
4. stuck thermostat
5. hoses collapsing.
6. Air lock in system
7. Bad fins on water pump.

Connie, Were the radiator,water pump and thermostat replaced to try and fix the over heat issue or as maintenance. Engine overheating can be caused by a lot of things, Leak in cooling system, air in system, bad rad. cap, slipping belt, faulty thermostat or installed upside down, faulty water pump, plugged radiator (inside/outside), collapsing rad hose, faulty cooling fan, leaking head gasket, sludge plugging engine water passages, poorly tuned engine, etc..
Take into a good shop for diagnoses and estimate for repair. Check the attached links,instruction and guides, Good luck
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How to Troubleshoot an Overheating Engine
Steve Litt Overheating Guide
Diagnose Engine Overheating Auto Repair Help
How to Troubleshoot an Overheating Engine DoItYourself com

You cant use straight water in the system. I hope that with the engine work, the water pump fins were inspected, the hoses were inspected for separation or collapse, the thermostat was replaced and installed correctly. The last thing that you need to check if all is correct is the temp of the coolant with an other thermometer. Oh and the radiator cap needs to be tested.

If you have changed the water pump AND the radiator AND the thermostat and still have the problem then the hoses should be checked to be sure they are not collapsing, also make sure that the coolant is 50/50 water and coolant and the thermostat is installed right.

Heres a couple of things you can check. Start your car and remove the radiator cap,(before it gets hot mind you) when it reaches norm operating temp, look inside radiator to see if water is circulating. If its not moving, its a bad water pump. Also, youre hoses should never collapse, if they collapse when they get hot maybe you need new hoses? Finally, if those dont work, flush out your radiator. Open the bottom cockpit and use a garden hose and let it flush out the system while the car is running, about 10 mins should do the trick. If the radiator looks clean inside then it doesnt need flushed.

the water pump collapsed, i am a ford master tech, replaced loads with timing belt

Believe it or not, new thermostats can be bad. Did you maybe get some adhesive on the thermostat preventing it to open fully? Is the thermostat installed with the crown up? The only other thing that I can think of, if it's a closed cooling system and the wrong radiator cap is installed, it won't hold the pressure, therefor overheating. The other thing may be the water pump. Many times the impellers will wear down internally causing to low of water flow.

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If the thermostat doesnt open hoses can **** in on them selfs Watch hoses while at operating temperature and rev the vehicle while watching the radiator hoses,top and bottom,to see if they stay normal.The bottom hose usualy has a steel inner winding to stop water pump from sucking hose in but have seen these corrode and collapse.I think you should replace the thermostat first and check that the fans are cooling the radiator correctly.Also check the accuracy of the water sensor that sends the signal to your dash gauge to make sure its not a simple sensor fault.Generaly a water pump will not give problems until it starts to leak.Have you bled the water system as air locks can cause your problem as well.good luck