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Running a car like yours without a thermostat is a recipe for overheating. Even when a thermostat it open, it still restricts coolant flow through the system. Without the thermostat, even while open, the coolant will go through the radiator to quickly for the heat-exhange process to work...thereby allowing superheated coolant to travel back into the engine and be completely ineffective.

Replacing the thermostat is a simple operation, and should be done at least every 100K miles. They are relatively cheap too. The boiling and pinging noises you heard are likely due to a stuck thermostat. Also, if you haven't done so, go ahead and change your radiator hoses too. They can weaken and kink, causing an excessive restriction of coolant flow.

The normal temperatures at highway speeds vs. overheating on surface streets makes me believe the thermostat isn't the problem. If a thermostat stick closed, you're going to overheat, no matter what. At highway speeds, you have forced air moving across your radiator, completing the heat-exhanger process. During stop and go driving, without the forced air flow across the radiator, your overheating, which indicates to me that there is an air flow problem. This could be diminished with lower ambient temps, but doesn't completely go away.

If you have electric fans, there is a thermo-fan switch that normally screws into the bottom of the radiator (usually with two wires going to it). This fan switch looks like a fat brass pipe plug with a couple of wires coming off it. The function of this switch is to tell the electric fans when to turn on and off, based on coolant temps in the bottom of the radiator. These switches do go bad...it's not uncommon. If the switch is not telling the fans to turn on, that would explain why you're overheating in stop-n-go driving. It is also possible that the electric fan motor has gone bad, and isn't spinning fast enough, or at all.

It doesn't sound like you have a blown head gasket or cracked block to me. However, it is possible to have a cracked head, which could allow exhaust gasses to superheat the coolant, but that doesn't fit your symptoms.

I recomment concentrating on the thermo-fan switch or the fan motor(s). But I would go ahead and replace the thermostat anyway. One last thing, many newer engines are equipped with small bypass hoses throughout the cooling system. I have seen many bypass hoses with an air bubble that couldn't escape, causing overheating problems. Make sure that none of the bypass hoses, if equipped, has an air lock.

I also second the previous post that recommended a Haynes manual. These are based on real-world experiences from regular joes. Good Luck!