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Russell wrote:I've had this car for 6 years, and it's served me well. It's just hard to think about taking on a car payment + student loan payments + credit card payments. I feel like I'm going to be drowning in debt soon

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Ah, I missed the boiling thing. Yes, if it is leaking cylinder pressure into the cooling system it would continue to "boil" after the car was shut off.

If you have a blown head gasket, or cracked the head, you would probably have white, sweet smelling smoke, coming out the exhaust. You would also be losing coolant at a noticeable rate for it to overheat because of a head problem. If there is no smoke, the most likely culprit is a bad thermostat (I know it was just replaced) or air in the cooling system. Before you throw a new thermostat at it, take out the current one and place it in a pot of water on the stove. Put a thermometer in the water and turn the burner on high. When the water hits about 190-195 the thermostat should open. If it doesn't open, or sticks open, its the problem. Whether it needs replaced or not, you should also bleed the cooling system.

If it isn't the thermostat, head gasket, cracked head, air in cooling system, a lack of coolant, or improper antifreeze mixture, I would suspect that the fan isn't functioning properly. I'm not familiar with your car, but if it has a belt driven fan and the belt is slipping it might not be providing enough airflow at idle to keep things cool.

If you don't have a service manual for the car GET ONE! It can save you lots and lots of money if you use it. I prefer Haynes manuals, but Chilton also makes an ok book.

Oh, and to answer your original question. Having the thermostat open all the time will also cause the engine to overheat. If it's open all the time coolant doesn't spend enough time in the radiator to transfer its heat.