Ok first off sorry about the accident. Glad you never got hurt. Second I had this problem on a diesil I had The engine block was cracked and was drawing air into the system. You haven`t said you have hard starting so its possible a guess right now. But what would happen is back pressure in the engine would block the flow of coolant throught the system. resulting in high temp. It would only occur after stop starts.
But here is another solution you can try. take the top off the rad and the expansion bottle (do only when cold) Undo the bottom hose on the radiator and then once completly drained fill the radiator with coolant rather than water. fill then close the radiatior and then fill the expansion tank to the full mark. Leave running 10 mins and then fill again if needed. You may have an airlock. This should cure it. If your temp rises still check the thermostate in a pan of boiling water and watch to see if it opens. If not then get a new one.