* Insufficient Airflow: At highway speeds, the Impala SS's radiator fan may not be needed because the forward motion pushes sufficient air through the radiator to cool the coolant. In stop-and-go traffic, this airflow dramatically decreases. If the radiator fan isn't working properly (weak motor, faulty switch, clogged fan shroud), the engine will overheat.
* Radiator Issues:
* Clogged Radiator: Over time, debris, bugs, and sediment can clog the radiator fins, reducing its cooling efficiency. This is exacerbated in slow traffic where the airflow is already compromised.
* Leaking Radiator: A leak, even a small one, will gradually reduce the coolant level, making the system less effective at dissipating heat. The pressure in the system builds when hot, and a small leak can become significant under pressure.
* Water Pump Issues: A failing water pump may not circulate coolant efficiently enough, especially when the engine is under high thermal load in slow traffic.
* Thermostat Issues: A thermostat stuck closed prevents coolant from circulating through the radiator, leading to overheating, particularly when the engine is working hard in slow-moving traffic. A thermostat stuck open *could* contribute to the problem if it's not allowing the coolant to reach a sufficient operating temperature, but this is less likely to cause overheating in stop-and-go traffic.
* Coolant Level: Low coolant level for any reason (leak, improper fill) severely reduces the system's cooling capacity.
* Head Gasket Failure: While less likely to manifest *only* in traffic, a failing head gasket can allow combustion gases to enter the cooling system, creating pressure and leading to overheating. This often presents with white smoke from the exhaust and milky residue in the coolant.
* Fan Clutch (if equipped): Some models might have a fan clutch instead of an electric fan. A failing fan clutch won't engage properly at lower speeds, leading to poor cooling in traffic.
Troubleshooting Steps:
1. Check the coolant level: Ensure the coolant reservoir is filled to the proper level (when cold).
2. Inspect the radiator: Look for leaks, dents, or significant clogging of the fins.
3. Test the radiator fan: Turn on the AC (should activate the fan) or use a jumper wire to directly power the fan to check if it works.
4. Check the thermostat: Ensure it opens and closes properly at the correct temperature.
5. Listen for unusual water pump noises: A failing water pump often makes a whining or groaning sound.
If you're not comfortable performing these checks yourself, take your Impala SS to a qualified mechanic for diagnosis and repair. Overheating can cause serious engine damage.
