Sounds like it may be only partially stuck open, it would not over heat if the thermostat was stuck open, it just would not reach operating temperature. Have you also checked the actual coolant level? Start with basic things, make sure the fans are coming on also while the car is at operating temp and at idle. Turn the air conditioner on, both fans should come on also.
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Monday, September 12th, 2016 AT 3:10 PM