overheating after a couple miles then return to normal

When an engine is started up from "cold" coolant is circulated in the engine by the water pump but is kept in the engine to encourage the engine coolant to get up to normal operating temperature as quickly as possible, (this decreases engine wear, reduces emitted emissions and allows the heater in the vehicle to provide heat for the passenger compartment quickly). The device that keeps the coolant in the engine and prevents it from entering the radiator is the thermostat. It should open when the engine reaches approximately 190 degrees Fahrenheit (depending on vehicle). If the thermostat fails to open the coolant does not flow to the radiator where it would under normal circumstances be cooled and drawn back into the engine to absorb more heat, get pumped back into the radiator to be cooled and drawn back into the engine again. For the cooling system to run hot intermittently I would suspect a sticking thermostat and would suggest replacing the thermostat and flushing the cooling system as a precaution. If you are stuck in traffic, no air is being pushed through the radiator as it would be if for example you were driving on the freeway at 60 miles and hour. While driving at speed rush air pushing through the radiator is sufficient to remove the heat of the coolant flowing through the radiator. When ambient air temperature is high and the vehicle is driven under load or heavily laden, the temperature gauge needle may be seen to rise toward the hot region of the temperature gauge (this is normal). With a radiator that is working efficiently after the gauge has been seen to rise above its normal operating temperature, the temperature gauge needle should be seen to drop toward normal when descending down hill under no engine load conditions when driving at freeway speeds. The radiator should be able to lower the temperature of the coolant in the radiator by approximately twenty degrees by utilizing air being forced through the radiator at freeway speeds. A radiator that is partially “plugged up” or restricted internally will decrease the cooling efficiency of the radiator particularly when the vehicle is driven under load. If the radiator cooling fins or tubes are damaged or blocked with road debris or mud cooling system efficiency will also be compromised. Engine running temperature can be verified by using a non-contact inferred heat detection gun. It is a non intrusive method of checking temperature used by most repair shops to verify temperature gauge accuracy and actual engine running temperature. When you are in traffic or when the engine overheats do you hear the electric fan operate? If not perhaps the cooling fan switch or control circuit has a problem.