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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

  1. A coolant temperature sensor is tested and reads 4.8V with the engine at normal operating temperature. Is this correct?

    Answer: No, the sensor should read approximately 0.5–1.5V when hot, indicating low resistance

    Coolant temperature sensors are NTC (negative temperature coefficient) thermistors; resistance drops as temperature rises, which causes the reference voltage signal voltage to fall to approximately 0.5–1.5V when hot.

  2. A vehicle's coolant level drops slowly over several weeks with no visible leaks and no symptoms. What is the likely cause?

    Answer: A small internal head gasket leak slowly burning coolant in the combustion chamber

    A minor head gasket breach can allow small amounts of coolant to enter the combustion chamber where it vaporizes; this produces no dramatic symptoms but explains slow, unexplained coolant loss.

  3. During a DFFT inspection, bubbles are observed rising from the coolant in the radiator with the cap removed and the engine running. What does this indicate?

    Answer: Combustion gases leaking into the cooling system through a failed head gasket

    Combustion gases forced into the cooling system by a head gasket failure create bubbles in the coolant that are visible in the radiator filler neck; this can be confirmed with a combustion leak test.

  4. A serpentine belt drives the water pump and alternator. What single symptom would indicate the belt has snapped?

    Answer: Simultaneous battery warning light and rapid engine overheating

    If the serpentine belt drives both the alternator and water pump, its failure will immediately stop coolant circulation (overheating) and alternator output (battery warning light) at the same time.

  5. What additive in coolant protects aluminum engine components from corrosion?

    Answer: Silicate or organic acid inhibitors (OAT/HOAT) specific to aluminum compatibility

    Modern coolants use organic acid technology (OAT) or hybrid organic acid technology (HOAT) inhibitor packages that form a protective film on aluminum surfaces to prevent corrosion.

  6. A vehicle is brought in after overheating. The engine has cooled but will not start. What is a likely consequence of severe overheating that prevents starting?

    Answer: A warped cylinder head causing low compression or a hydrolock condition from coolant in cylinders

    Severe overheating can warp the cylinder head, causing loss of compression and combustion seal; coolant can also be drawn into cylinders, creating a hydrolock condition that prevents engine rotation.