DFFT Cooling Systems 2

Question 1

Coolant is found mixed with engine oil, appearing as a milky substance on the dipstick. What is the likely cause?

Accepted Answer

A failed head gasket or cracked cylinder head allowing coolant into the oil passages

Answer

Coolant in the oil produces a milky, creamy appearance; the most common cause is a head gasket failure that opens a pathway between the water jacket and oil passages.

Question 2

Electrolytic corrosion is found on the radiator cores and cooling system fittings. What is the cause?

Accepted Answer

Depleted corrosion inhibitors in old coolant allowing electrochemical reactions between dissimilar metals

Answer

Modern coolant contains corrosion inhibitors that become depleted over time; without inhibitors, the coolant becomes electrolytic and causes galvanic corrosion between aluminum and steel components.

Question 3

A water pump is removed and found to have eroded impeller vanes. What caused this condition?

Accepted Answer

Cavitation from low coolant levels or depleted coolant causing erosion of the impeller

Answer

Cavitation occurs when vapor bubbles form and implode against the impeller surface; this is caused by low coolant, incorrect mixture ratio, or overly high pump speed, and erodes the impeller metal over time.

Question 4

After replacing a thermostat, the cooling system must be bled. Why is this step critical?

Accepted Answer

Air pockets prevent proper coolant flow, causing hot spots and inaccurate temperature readings

Answer

Air is a poor conductor of heat compared to coolant; trapped air pockets prevent effective heat transfer, cause overheating in specific areas, and can lead to erratic temperature gauge readings.

Question 5

A vehicle's cooling system is pressurized to 16 psi and holds for 10 minutes, but the engine still overheats. What should be suspected?

Accepted Answer

A combustion gas leak into the coolant caused by a head gasket failure

Answer

A head gasket can fail in a way that only leaks combustion gases into the coolant without leaking coolant externally; this introduces non-condensable gas that reduces cooling efficiency.

DFFT - Driver Fault Finding Test Practice Test

DFFT - Driver Fault Finding Test Practice Test

DFFT Cooling Systems 2