ASE A1 Engine RepairLubrication and Cooling SystemsEasy
A technician is diagnosing an engine that consistently runs cold, causing poor fuel economy and reduced heater output. The coolant level is full. Which component is the most likely cause?
- AA clogged radiator
- BA faulty water pump
- CAn airlock in the cooling system
- DA stuck-open thermostat
Show answer & explanationAnswer & explanation
Correct answer: D. A stuck-open thermostat
A thermostat that is stuck in the open position allows coolant to constantly flow through the radiator, preventing the engine from reaching its optimal operating temperature. This leads to the engine running cold, which negatively impacts fuel economy and heater performance.
Why the other options are wrong
- A. A clogged radiator would cause overheating due to restricted coolant flow and poor heat dissipation, not cold running.
- B. A faulty water pump would typically cause overheating due to lack of circulation, not consistently cold operation.
- C. An airlock could cause overheating or erratic temperature readings, but not consistent cold running with a full coolant level.
Stuck-Open Thermostat
A thermostat stuck in the open position constantly allows coolant to flow through the radiator, preventing the engine from reaching its optimal operating temperature, leading to cold running conditions.
- Engine runs cold or warms up slowly
- Poor fuel economy
- Reduced cabin heater output
Memory trick: Engine's chilly? Thermostat's silly!