What should a thermocouple cylinder-head temperature indicator read when the engine is cold?

What should a thermocouple cylinder-head temperature indicator read when the engine is cold?

• A. Zero
• B. The same as the outside air temperature gauge
• C. Ambient room temperature
• D. Oil temperature

Answer: (B)

When the engine is cold, there’s no heat coming from combustion to raise the cylinder head above ambient temperature. The thermocouple in the cylinder head will then read the surrounding air temperature, which on the aircraft is the outside air temperature. So the cylinder-head temperature indicator shows the same reading as the outside air temperature gauge. The other options don’t fit because zero would imply a fault or no power, ambient room temperature isn’t the normal reference for an aircraft engine on the ramp, and oil temperature reflects the oil’s condition, not the ambient environment.

When the engine is cold, there’s no heat coming from combustion to raise the cylinder head above ambient temperature. The thermocouple in the cylinder head will then read the surrounding air temperature, which on the aircraft is the outside air temperature. So the cylinder-head temperature indicator shows the same reading as the outside air temperature gauge. The other options don’t fit because zero would imply a fault or no power, ambient room temperature isn’t the normal reference for an aircraft engine on the ramp, and oil temperature reflects the oil’s condition, not the ambient environment.