ASE Heating and Cooling 5 — Questions and Answers
Question 1: An infrared thermometer scan of a warm radiator shows several cold vertical bands. What does this indicate?
- Normal thermostat operation
- Plugged radiator tubes (Correct answer)
- Air in the heater core
- Faulty radiator cap
Correct answer: Plugged radiator tubes
Cold spots across a radiator show tubes with no coolant flow, which usually means internal clogging.
Question 2: When a thermostat is bench-tested in heated water, it should:
- Open fully at room temperature
- Start to open near its rated temperature (Correct answer)
- Stay closed until the water boils
- Open only when pressure is applied
Correct answer: Start to open near its rated temperature
A good thermostat starts to open close to its stamped temperature and opens fully about 20°F above it.
Question 3: How should a thermostatic (viscous) fan clutch behave when the engine is at full operating temperature?
- Freewheel with no resistance
- Lock up more and resist being turned (Correct answer)
- Turn in the opposite direction
- Disconnect from the water pump
Correct answer: Lock up more and resist being turned
A heated bimetal spring engages a viscous clutch, which increases fan speed and resistance when cooling is needed.
Question 4: With the engine running, steady bubbles are seen in the coolant reservoir and coolant is pushed out of the overflow. What is the most likely cause?
- Faulty thermostat
- Head gasket failure or cracked cylinder head (Correct answer)
- Weak water pump
- Inoperative cooling fan
Correct answer: Head gasket failure or cracked cylinder head
Combustion gas forced into the cooling system shows up as continuous bubbles and pushes coolant out.
Question 5: How should a thermostat be installed?
- With the temperature-sensing pellet facing the engine (Correct answer)
- With the pellet facing the radiator
- In either direction
- With the jiggle valve at the bottom
Correct answer: With the temperature-sensing pellet facing the engine
The wax pellet has to sit in engine coolant to sense engine temperature, so it faces the engine.
Question 6: What is the purpose of a cooling system bypass passage or hose?
- To send coolant to the radiator when the thermostat is open
- To circulate coolant through the engine while the thermostat is closed (Correct answer)
- To vent air from the radiator cap
- To feed coolant to the transmission cooler
Correct answer: To circulate coolant through the engine while the thermostat is closed
The bypass keeps coolant moving through the block and head while the thermostat is closed, which prevents hot spots during warm-up.
Question 7: Technician A says a faulty radiator cap can cause coolant loss. Technician B says a faulty radiator cap can cause the engine to overheat. Who is correct?
- Technician A only
- Technician B only
- Both A and B (Correct answer)
- Neither A nor B
Correct answer: Both A and B
A cap that won't hold pressure lowers the boiling point, which leads to boil-over, coolant loss, and overheating.
ASE Heating and Cooling 5
An infrared thermometer scan of a warm radiator shows several cold vertical bands.
What does this indicate?