ASE A1 Engine RepairLubrication and Cooling SystemsMedium
A client complains that their vehicle's engine is constantly overheating, especially during highway driving. The technician observes that the radiator cooling fan is operating correctly, and the coolant level is full. Which of the following is the most likely cause of this overheating condition?
- AFaulty thermostat stuck open
- BLoose accessory drive belt
- CClogged radiator fins or internal passages
- DRestricted exhaust system
Show answer & explanationAnswer & explanation
Correct answer: C. Clogged radiator fins or internal passages
If the cooling fan and coolant level are adequate, and overheating occurs at higher loads (like highway driving), a restricted radiator (either externally clogged fins or internally clogged passages) is a very common cause because it prevents efficient heat transfer.
Why the other options are wrong
- A. A thermostat stuck open would cause the engine to run cold, not overheat.
- B. A loose accessory drive belt would likely cause the water pump to slip, leading to overheating, but often accompanied by a squealing noise and potentially other issues like power steering or alternator problems. The question specifies 'radiator cooling fan is operating correctly'.
- D. A restricted exhaust system can cause overheating due to increased engine load and heat, but a clogged radiator is a more direct and common cause in the cooling system itself.
Radiator Restriction
A condition where the flow of air through the radiator fins or coolant through its internal passages is impeded, reducing its ability to dissipate heat.
- Can be caused by external debris (leaves, bugs) or internal corrosion/deposits.
- Leads to engine overheating, especially under load.
- Often diagnosed by temperature differences across the radiator or visual inspection.
Memory trick: Overheating is a hot mess; check the flow, then address.