Car overheats water doesn't circulate. No heat. We changed thermostats. Worked good a couple days. Drove up to store about 2 miles overheated no heat. Shut it off drove slow heat came on sped up lost heat needle went to hot any ideas what it could be? Radiator stays cold.

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    Welcome to Motor Vehicle Maintenance & Repair! What is the year/make/model/engine of the car in question? Nov 1 '17 at 2:02

Lack of coolant circulation is usually caused by 3 things:

  • closed thermostat
  • faulty water pump
  • blocked passage or hose

Since you changed the thermostat, we could likely rule that out. So:

  • inspect your water pump belt, make sure it is tight and not slipping
  • inspect your water pump pulley, make sure it is on securely and driving the pump
  • remove your water pump and inspect the blades inside
  • turn the pump by hand, make sure it is free to move

If everything checks out, you likely have a blocked coolant passage inside the engine block. Drain your coolant and fill up the system with a household product that removes Calcium Lime and Rust deposits. Run the engine to temperature and run your heater on hot so that the cleaner can circulate everywhere. Drain the cleaner and replace with proper coolant, then go for a drive.

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    I'd add that if you actually do all that work to remove a water pump, get a new one. Don't put the old one back in because you've already done the work to replace it.
    – JPhi1618
    Nov 1 '17 at 13:53

Pull the thermostat : put it back together: keep the radiator cap off: start it up and see if the water flows through the radiator if the water is not moving I would go with a bad pump: but the water is moving and blowing out the top of the radiator and I look for a blockage somewhere heater core or you could run a bypass hose and Bypass the heater so you check for eng blockage:::

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