The gurgling noise tells me it's overheating. As far as the heat, I would think the hotter the engine, the hotter the heat. Therefore, it leads me to believe there is a blockage. If the fan's are working, it shouldn't heat up when stopped. . The thermostat doesn't fit as a problem. I question a partial blockage in the radiator (flush) or a water pump going bad.
With the engine cold, open the radiator. Start the car and allow to warm up. When it hits a normal operating temp, the t-stat should be open and allowing full flow of the coolant which you should be able to see in the radiator.
Let me know what you find. Also, feel both upper and lower rad hoses for temp, and both heater core hoses.
Joe
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Saturday, January 10th, 2009 AT 8:50 PM