Heating and Cooling Flashcards

An infrared thermometer scan of a warm radiator shows several cold vertical bands. What does this indicate?

Answer: Plugged radiator tubes

Cold spots across a radiator show tubes with no coolant flow, which usually means internal clogging.

When a thermostat is bench-tested in heated water, it should:

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.

How should a thermostatic (viscous) fan clutch behave when the engine is at full operating temperature?

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.

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?

Answer: Head gasket failure or cracked cylinder head

Combustion gas forced into the cooling system shows up as continuous bubbles and pushes coolant out.

How should a thermostat be installed?

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.

What is the purpose of a cooling system bypass passage or hose?

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.

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?

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.