Cooling Systems Flashcards
6 cards from real DFFT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Cooling Systems flashcards as text
Coolant is found mixed with engine oil, appearing as a milky substance on the dipstick. What is the likely cause?
Answer: A failed head gasket or cracked cylinder head allowing coolant into the oil passages
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.
Electrolytic corrosion is found on the radiator cores and cooling system fittings. What is the cause?
Answer: Depleted corrosion inhibitors in old coolant allowing electrochemical reactions between dissimilar metals
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.
A water pump is removed and found to have eroded impeller vanes. What caused this condition?
Answer: Cavitation from low coolant levels or depleted coolant causing erosion of the impeller
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.
After replacing a thermostat, the cooling system must be bled. Why is this step critical?
Answer: Air pockets prevent proper coolant flow, causing hot spots and inaccurate temperature readings
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.
A vehicle's cooling system is pressurized to 16 psi and holds for 10 minutes, but the engine still overheats. What should be suspected?
Answer: A combustion gas leak into the coolant caused by a head gasket failure
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.
What is the correct antifreeze-to-water ratio for most US passenger vehicles for year-round protection?
Answer: 50% antifreeze and 50% distilled water
A 50/50 mixture of ethylene glycol antifreeze and distilled water provides freeze protection to approximately -34°F and boil protection to approximately 265°F while maintaining proper heat transfer.