Engine overheating specifically in traffic or at low speeds in your 2018 Jeep Grand Cherokee indicates the cooling system can't dissipate heat without adequate airflow. While highway driving provides natural airflow, idle and city driving depend on the cooling fans to maintain temperature.
Why Overheating Occurs in Traffic
At highway speeds, air flowing through the radiator removes heat efficiently. In traffic, without this airflow, the electric cooling fans must provide air movement. If fans fail to engage or provide insufficient airflow, heat builds faster than the cooling system can remove it.
Common Causes
Failed or sluggish cooling fans top the list of traffic overheating causes. Thermostat stuck closed prevents coolant circulation. Water pump impeller wear reduces coolant flow. Low coolant level from leaks or neglect limits heat transfer capacity. Clogged radiator restricts airflow or flow-through.
Cooling Fan Operation
The Grand Cherokee uses electric cooling fans controlled by the PCM based on coolant temperature and A/C operation. Sensor failures, relay problems, or fan motor issues prevent proper engagement. Fans should activate when coolant reaches approximately 220°F or when A/C is on.
System Pressure Important
The cooling system operates under pressure, raising the boiling point above 212°F. A failed radiator cap that can't hold pressure allows coolant to boil prematurely, especially in traffic conditions where temperatures climb higher.