ASE A1 Engine RepairLubrication and Cooling SystemsHard
A vehicle owner reports that their engine frequently runs hot, especially when driving at highway speeds, but the temperature gauge returns to normal when driving slowly in city traffic. The technician verifies the coolant level is full and the cooling fan operates correctly. Which of the following is the MOST likely cause?
- AA clogged radiator
- BA faulty thermostat
- CA failing water pump
- DAn air lock in the cooling system
Show answer & explanationAnswer & explanation
Correct answer: A. A clogged radiator
An engine overheating at highway speeds but returning to normal in city traffic (where the cooling fan provides airflow) is a classic symptom of a partially clogged radiator. At high speeds, the engine produces more heat, and the clogged radiator cannot dissipate it effectively. In city traffic, the fan compensates for the reduced natural airflow, temporarily masking the issue.
Why the other options are wrong
- B. A faulty thermostat (stuck closed) would cause overheating at all speeds, or (stuck open) would cause the engine to run cold.
- C. A failing water pump would typically cause overheating at all speeds due to insufficient coolant circulation.
- D. An air lock usually causes erratic temperature readings and overheating at various conditions, not specifically at highway speeds and recovering in city traffic.
Clogged Radiator
A radiator with internal blockages (e.g., corrosion, debris, scale) that restrict coolant flow and reduce its ability to dissipate heat.
- Reduces cooling system efficiency.
- Commonly causes overheating, especially under load or at high speeds.
- Can lead to engine damage if not addressed.
Memory trick: Highway hot, city cool? Radiator's playing a fool!