ASE A1 Engine RepairLubrication and Cooling SystemsMedium
A technician is diagnosing an engine with a persistent overheating issue despite a recently replaced thermostat and a full coolant level. The upper radiator hose is hot, but the lower radiator hose remains cool. Which of the following is the most likely cause?
- AAn airlock in the cooling system
- BA failing water pump
- CA faulty radiator fan switch
- DA clogged radiator
Show answer & explanationAnswer & explanation
Correct answer: D. A clogged radiator
If the upper hose is hot and the lower hose is cool, it indicates that hot coolant is entering the radiator but is not flowing through and cooling down effectively. This is a classic symptom of a restricted or clogged radiator, preventing heat exchange.
Why the other options are wrong
- A. An airlock can cause overheating, but it usually prevents proper circulation entirely or causes erratic temperature readings, not typically this specific hose temperature differential.
- B. A failing water pump would typically result in both hoses being cool or a lack of circulation, not just the lower hose being cool while the upper is hot.
- C. A faulty radiator fan switch would primarily cause overheating at low speeds or idle, but wouldn't explain the temperature difference across the radiator.
Clogged Radiator Symptoms
A clogged radiator restricts coolant flow and heat exchange, leading to engine overheating and significant temperature differences between the upper and lower radiator hoses.
- Upper hose hot, lower hose cool
- Engine overheating at various speeds
- Reduced heater performance
Memory trick: Hot up, cool down? Radiator's frown!