2009 Chevrolet Malibu - still overheating after thermostat change

Changed the thermostat because of over heating. Found melted plastic on it. Car is still over heating. Any thoughts as to the cause?

Could be many things. I would suggest you keep a close eye on the coolant level and temp gauge, and get it to a pro for diagnosis ASAP.

Cooling fan is not working . guessing it has an electric cooling fan and it’s never turning on when it gets hot .

When the engine is cold, remove the pressure cap from the cooling system surge tank.

Start the engine, and as the engine idles watch the coolant in the surge tank.

If bubbles begin to form in the coolant, that’s an indication of a blown head gasket.


When it is overheating the radiator cooling fan(s) should be spinning like crazy. Pop the hood to check if they are spinning or not.

The fans are working. Thanks for the response.

The best things in life are not things…live well.

If the fans are working, and thermostat is known good and installed w/correct orientation, overheating is most likely due to one of the following

  • low coolant level in radiator
  • water pump not pumping to spec
  • radiator not flowing to spec
  • cooling system not maintaining the correct pressure
  • exhaust gasses are leaking into the coolant due to an incontinent head gasket

Failure to maintain the correct pressure in the cooling system is pretty common. If you want to make a guess and feel lucky, you could try replacing the pressure cap yourself. If that doesn’t solve it – for which there is much doubt it will — then you’ll have to have a shop do the normal cooling system tests: holding pressure, water pump flow rate, radiator flow rate, head gasket leak, engine timing, fuel trims, fan spinning rate, etc.

If the thermostat you have now hasn’t been visually water bath tested in a pan of water on the stove, suggest to do that first. Replacement thermostats fail new, right out of the box sometimes.

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