ASE G1 Auto Maintenance and Light RepairEngine SystemsMedium
A vehicle's engine is experiencing consistent overheating, even after replacing the thermostat and ensuring the coolant level is correct. The upper radiator hose is hot and firm, but the lower radiator hose remains cool. What is the most probable cause of this condition?
- AAn airlock in the cooling system
- BA faulty water pump
- CA malfunctioning coolant temperature sensor
- DA restricted heater core
Show answer & explanationAnswer & explanation
Correct answer: B. A faulty water pump
If the upper hose is hot (indicating hot coolant is leaving the engine) but the lower hose is cool (indicating coolant is not circulating back to the engine or through the radiator), and the thermostat and coolant level are good, the water pump is the most likely culprit for failing to circulate coolant.
Why the other options are wrong
- A. An airlock can cause overheating, but the specific hot upper/cool lower hose symptom, especially after thermostat replacement, points more directly to a circulation failure.
- C. A malfunctioning coolant temperature sensor would affect gauge readings or engine management, not directly prevent coolant circulation in this manner.
- D. A restricted heater core would primarily affect cabin heat, not typically cause overall engine overheating with this specific hose temperature differential.
Water Pump Failure Symptoms
Symptoms of a failing water pump include engine overheating, visible coolant leaks from the pump, and sometimes a whining noise from the pump pulley.
- Primary function is coolant circulation.
- Failure causes overheating due to lack of flow.
- Hot upper hose, cool lower hose is a key indicator.
Memory trick: Hot top, cold bottom, no flow, pump's rotten.