Postal Automotive Technician Exam Prep Guide 2026: Systems, Maintenance, and Troubleshooting

Power impulses from the engine are smoothed out by the A. Camshaft B. Crankcase C. Flywheel D. Piston rings Rationale: The flywheel stores rotational energy and smooths out power impulses. Camshafts and pistons do not perform this function. The vibration damper on an auto engine is fastened to the A. Transmission B. Flywheel C. Crankshaft D. Oil pump Rationale: The vibration damper attaches to the crankshaft to absorb torsional vibrations. It is not connected to the flywheel or oil pump. Hard starting is very often caused by A. Strong battery B. Tight piston rings C. Improper choke operation D. Clean air filter Rationale: A malfunctioning choke restricts proper air-fuel mixture during cold starts, causing hard starting. A clean filter doesn’t cause this problem. A car with a history of burned points would probably indicate A. Weak ignition coil B. Loose timing belt C. Too high setting of the voltage regulator D. Dirty air filter Rationale: Excessive voltage overheats and burns ignition points. This is usually due to an overcharging voltage regulator. When reconditioning brake drums, the maximum allowable oversize is A. .020 inches B. .040 inches C. .060 inches D. .100 inches Rationale: Exceeding .060 inches oversize weakens the drum and impairs braking. Smaller sizes are within safe limits. The amount of air-fuel mixture taken into the cylinder on the intake stroke is a measure of the engine’s A. Brake horsepower B. Torque ratio C. Volumetric efficiency D. Compression ratio Rationale: Volumetric efficiency indicates how effectively the cylinder fills with the air-fuel mixture during the intake stroke. Welch plugs are installed on engines to provide A. Extra cooling B. Extra compression C. A means of removing the sand after casting D. Better lubrication Rationale: Welch (freeze) plugs allow removal of sand used in casting the engine block. They’re not for cooling or compression directly. The two-cycle engine produces a power stroke with every A. Two strokes of the piston B. Two revolutions of the crankshaft C. One revolution of the crankshaft D. Four strokes of the piston Rationale: In a two-stroke engine, every crankshaft revolution produces one power stroke, unlike four-stroke engines. Preignition may be caused by A. Low compression B. Lean mixture C. Carbon deposits D. Cold spark plug Rationale: Carbon deposits retain heat and ignite the mixture early (preignition). Lean mixtures more often cause detonation, not preignition. The size of an outboard motor propeller is given in A. Horsepower and thrust B. Length and width C. Diameter and pitch D. Radius and torque Rationale: Propeller size is defined by diameter and pitch, which determine water displacement and engine load. Closed crankcase ventilation systems are used to A. Increase fuel economy B. Cool the engine faster C. Aid in prevention of air contamination D. Warm the intake manifold Rationale: These systems recycle crankcase vapors back to the intake to reduce pollution. They don't significantly affect cooling or fuel economy. The angular motion about the vertical axis of an aircraft is known as A. Pitch B. Roll C. Yaw D. Drift Rationale: Yaw is rotation around the vertical axis. Pitch is around the lateral axis, and roll around the longitudinal axis. The carburetor circuit that maintains a constant fuel level in the float bowl is the A. Idle circuit B. Main circuit C. Float circuit D. Power circuit Rationale: The float circuit controls the needle valve to maintain fuel level. Other circuits manage mixture delivery during specific engine loads. A jet engine combustion chamber liner is cooled by A. Liquid fuel B. Oil circulation C. Air streams D. Coolant fluid Rationale: Air is directed around the liner to cool it and prevent overheating. Jet engines don’t use liquid coolant systems. Regenerative gas turbine engines have been successfully developed for use on A. Motorcycles B. Boats C. Automobiles D. Helicopters Rationale: Regenerative turbines reuse exhaust heat to improve efficiency and have been tested in automobiles more than other options. In a generator system, excessive output voltage is usually controlled by the A. Field windings B. Voltage regulator C. Armature resistance D. Battery cables Rationale: The voltage regulator maintains proper system voltage. Field windings and armatures cannot regulate voltage on their own. The main purpose of piston rings is to A. Cool the cylinder walls B. Seal the combustion chamber C. Lubricate the crankshaft D. Increase fuel pressure Rationale: Piston rings prevent gas leakage and maintain compression. They don’t control fuel pressure or crankshaft lubrication. Detonation in an engine is caused primarily by A. Cold spark plugs B. Low engine temperature C. High combustion temperatures and pressures D. Thick engine oil Rationale: Detonation occurs when fuel-air mixture explodes violently due to high temperature and pressure. Oil and spark plug temperature are unrelated. The primary purpose of a thermostat in an engine cooling system is to A. Increase coolant pressure B. Prevent coolant leaks C. Regulate engine temperature D. Speed up fuel combustion Rationale: The thermostat maintains optimal engine operating temperature by opening and closing to control coolant flow. An alternator produces electricity when its A. Field windings stay stationary B. Rotor spins inside the stator C. Battery is discharged D. Voltage regulator is bypassed Rationale: Alternators generate electricity by rotating a magnetic rotor inside a stationary stator to induce current. A clogged air filter will cause the engine to run A. Lean B. Rich C. At higher RPM D. With higher oil pressure Rationale: A clogged air filter reduces airflow, causing a rich air-fuel mixture. It doesn’t increase oil pressure or RPM. The purpose of a muffler in the exhaust system is to A. Increase horsepower B. Reduce engine noise C. Cool exhaust gases D. Improve fuel economy Rationale: Mufflers reduce sound from exhaust gases. They don’t significantly change fuel economy or horsepower. In an internal combustion engine, the camshaft is driven by the A. Crankshaft B. Alternator C. Timing belt or chain D. Fuel pump Rationale: The timing belt/chain connects the crankshaft to the camshaft to maintain synchronized valve timing. A slipping clutch in a manual transmission vehicle is often caused by A. Low brake fluid B. Worn piston rings C. Worn clutch disc D. Damaged spark plug wires Rationale: A worn clutch disc loses friction, causing slip. Spark plug wires and piston rings don't affect clutch operation. The device that stores electrical energy in a vehicle to start the engine is the A. Alternator B. Starter motor C. Battery D. Distributor Rationale: The battery provides the electrical power needed to crank the engine. The alternator only charges it. Excessive blue exhaust smoke indicates A. Rich fuel mixture B. Overheated engine C. Burning engine oil D. Faulty fuel injectors Rationale: Blue smoke means oil is being burned in the combustion chamber. Rich mixtures produce black smoke instead. The function of the radiator cap is to A. Prevent coolant evaporation B. Maintain proper pressure in the cooling system C. Lubricate the water pump D. Increase coolant flow Rationale: Radiator caps regulate cooling system pressure to raise the boiling point of coolant. Low engine compression is most likely caused by A. Rich fuel mixture B. Low oil level C. Worn piston rings or valves D. Strong spark Rationale: Low compression results from leaking valves or worn rings. Fuel mixture or spark does not affect compression directly. The purpose of the choke in a carburetor is to A. Increase air supply B. Heat fuel C. Restrict air to create a rich mixture during cold start D. Increase ignition timing Rationale: The choke enriches the mixture by restricting air during cold starts. It doesn’t affect ignition timing or fuel heating. Most small gas engines use a _________ ignition system A. Battery B. Magneto C. Electronic module D. Coil and distributor Rationale: Magneto ignition generates its own electricity and is widely used in small engines. Battery or coil systems depend on external power sources, making them less suitable for small engines. Icing occurs most often A. On hot dry days B. On cool damp days C. In warm weather only D. In cold dry weather Rationale: Cool, moist air promotes carburetor icing. Dry or hot conditions lack sufficient moisture for ice formation. The function of the float in a carburetor is to A. Increase fuel pressure B. Close the needle valve C. Cool the intake mixture D. Regulate exhaust gases Rationale: The float controls fuel level by closing the needle valve when the fuel bowl is full. It doesn’t affect cooling or exhaust regulation. To improve stability when cornering, manufacturers added a device called A. Control arm B. Ball joint C. Stabilizer bar D. Tie rod Rationale: Stabilizer bars reduce body roll during cornering, enhancing vehicle stability. Tie rods and ball joints are for steering, not stabilization. Adjustment of the rods on a car will affect A. Camber B. Caster C. Toe-in D. Ride height Rationale: Tie rod adjustments affect toe alignment. Camber and caster require different suspension adjustments. A restriction in the exhaust system is indicated on a vacuum gauge by a A. Sudden drop in reading B. Gradual decrease in reading C. Constant high reading D. Fluctuating reading Rationale: A slowly decreasing vacuum reading suggests rising back pressure from an exhaust restriction. Sudden drops indicate intake or valve issues. Disc brakes on a car have a distinct advantage over drum brakes in that they A. Are cheaper B. Require less fluid C. Fade less when hot D. Need no maintenance Rationale: Disc brakes dissipate heat better, reducing brake fade. They are not cheaper or maintenance-free. In a diesel engine, the fuel is ignited by A. Spark plug B. Glow plug spark C. Heat of compression D. External heater Rationale: Diesel engines rely on high compression to generate heat to ignite fuel. Spark plugs are not used in diesel engines. Engine timing is generally set by using a A. Tachometer B. Timing belt C. Strobe light D. Pressure gauge Rationale: A strobe light shows timing marks while the engine runs, enabling precise ignition timing. Tachometers only measure RPM. If an engine operates long periods at part throttle, the A. Pistons will overheat B. Spark plugs will become covered with carbon C. Fuel will overheat D. Oil pressure will increase Rationale: Part throttle operation causes incomplete combustion, leading to carbon deposits on spark plugs. Leaking intake valve guides will cause A. Low oil pressure B. Engine overheating C. Excessive oil consumption D. Low fuel pressure Rationale: Oil leaks through worn intake valve guides into the combustion chamber, causing high oil consumption and smoke. Flooding of a carburetor is generally caused by A. Dirty air filter B. A stuck float needle valve C. Weak fuel pump D. Low oil level Rationale: A stuck needle valve prevents fuel shutoff, causing overflow (flooding). Air filters and oil levels do not cause flooding. On many cars, the fuel pump is combined with the A. Brake booster B. Alternator C. Vacuum pump D. Radiator fan Rationale: Mechanical fuel pumps are often integrated with vacuum pumps for windshield wipers or brake boosters. Carbon fouling of a spark plug is an indication of A. Lean fuel mixture B. Too rich a mixture C. High octane fuel D. Tight valve clearance Rationale: Excess fuel (rich mixture) leads to unburned carbon deposits on spark plugs. Lean mixtures do the opposite. If generator output is excessive even after the F terminal is disconnected, the cause may be A. Voltage regulator B. Broken fan belt C. The generator D. Dead battery Rationale: If disconnecting the field (F) terminal doesn’t reduce output, the generator is internally faulty. An automobile alternator converts AC to DC by means of A. Capacitors B. Brushes C. Silicon diodes D. Resistors Rationale: Diodes in the rectifier convert AC produced by the alternator into DC. Capacitors only smooth voltage.