Engine Systems and Repair Flashcards

What is the purpose of the thermostat bypass circuit in an engine cooling system?

Answer: To circulate coolant within the engine block before the thermostat opens

The bypass circuit allows coolant to circulate through the engine block and cylinder head before the thermostat opens, ensuring even heat distribution and preventing hot spots during warmup.

An engine has low oil pressure at idle but normal pressure at higher RPM. What is the most likely cause?

Answer: Worn oil pump or excessive bearing clearances

Worn oil pump gears or excessive bearing clearances allow oil to leak past faster than the pump can supply at low RPM. At higher RPM, the pump output overcomes the leakage, restoring normal pressure.

What is the correct sequence for tightening cylinder head bolts?

Answer: Centre-outward spiral pattern in multiple steps

Cylinder head bolts are tightened from the centre outward in a spiral pattern and in multiple progressive steps to ensure even clamping force across the head gasket and prevent warping.

What causes piston ring flutter?

Answer: Engine RPM exceeding the ring's ability to maintain contact with the cylinder wall

Piston ring flutter occurs at high RPM when the inertia of the ring overcomes the gas pressure and ring tension holding it against the cylinder wall, causing a loss of sealing and blow-by.

What is the purpose of the oil squirter (piston cooling jet) found in some engines?

Answer: To spray oil onto the underside of the piston for cooling

Oil squirters spray pressurized oil onto the underside of the piston to cool it, preventing detonation, reducing thermal stress, and extending piston life, especially in turbocharged and high-performance engines.

What does a cylinder power balance test determine?

Answer: The relative contribution of each cylinder to overall engine power

A power balance test disables one cylinder at a time and measures the RPM drop. A cylinder contributing less power will cause a smaller RPM drop when disabled, indicating a problem.