ASE G1 Auto Maintenance and Light RepairEngine SystemsHard
A vehicle's engine consistently runs at a higher-than-normal temperature, and the upper radiator hose is very hot and firm, while the lower radiator hose remains relatively cool. The coolant level is full. What is the MOST likely cause?
- AClogged radiator
- BFaulty engine coolant temperature (ECT) sensor
- CStuck-open thermostat
- DLow engine oil level
Show answer & explanationAnswer & explanation
Correct answer: A. Clogged radiator
If the upper radiator hose is hot (indicating hot coolant leaving the engine) and the lower radiator hose is cool (indicating coolant is not flowing effectively through the radiator to be cooled), with a full coolant level, it points to a restriction in the radiator. A clogged radiator prevents heat exchange, leading to overheating.
Why the other options are wrong
- B. A faulty ECT sensor could cause the gauge to read incorrectly or affect engine management, but it wouldn't cause the physical temperature difference in the hoses or actual overheating in this manner.
- C. A stuck-open thermostat would cause the engine to run *too cool* or take a long time to warm up, not overheat.
- D. Low engine oil level primarily affects lubrication and can cause overheating, but it wouldn't directly explain the specific hot-upper/cool-lower radiator hose symptom.
Clogged Radiator Symptoms
Indicators that the radiator's internal passages are blocked, restricting coolant flow and preventing proper heat dissipation from the engine's cooling system.
- Engine overheating, especially at higher RPMs or loads.
- Significant temperature difference between upper (hot) and lower (cool) radiator hoses.
- Coolant flow restriction, despite a full coolant level.
Memory trick: A 'CLOGGED' radiator makes the 'TOP' hot and the 'BOTTOM' cold.