ASVAB Practice Test · Auto Information
ASVAB Practice Test: Automotive Systems Concepts
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Overview
This chapter covers how cars and trucks work. You will review the engine and its four-stroke cycle, the fuel, ignition, and cooling systems, and the brakes, steering, suspension, and electrical parts. Questions often ask what a part does or what causes a common problem.
Most gasoline engines use a four-stroke cycle. On the intake stroke, the piston moves down and pulls in air and fuel. On the compression stroke, the piston moves up and squeezes the mixture. A spark plug then fires for the power stroke, which pushes the piston down, and the exhaust stroke pushes the burned gases out.
The cooling system keeps the engine from overheating. A water pump moves coolant through the engine, the radiator gives off the heat to the air, and the thermostat controls when coolant flows to the radiator. The lubrication system uses oil to reduce friction between moving parts.
Most cars use hydraulic brakes, where pressing the pedal pushes brake fluid from the master cylinder to each wheel. Disc brakes use pads that squeeze a rotor, and drum brakes use shoes that press against a drum. The battery starts the car, and the alternator recharges the battery and powers the electrical system while the engine runs.
Key concepts
Four-stroke cycle
Intake (air and fuel come in), compression (the mixture is squeezed), power (the spark ignites it and pushes the piston down), exhaust (burned gas goes out).
Memory tipSuck, squeeze, bang, blow.
Ignition system
Creates the spark that lights the fuel in a gasoline engine. The ignition coil raises the voltage, and the spark plug makes the spark in the cylinder.
Memory tipDiesel engines use compression heat, not spark plugs.
Cooling system
The water pump circulates coolant, the radiator releases engine heat to the air, and the thermostat opens to send coolant to the radiator when the engine warms up.
Memory tipA stuck-closed thermostat causes overheating.
Hydraulic brakes
Pressing the pedal pushes fluid from the master cylinder through lines to each wheel. Disc brakes squeeze a rotor with pads; drum brakes press shoes against a drum.
Memory tipPads go with rotors, shoes go with drums.
Battery and alternator
The battery supplies power to start the engine. The alternator, driven by the engine, makes electricity to recharge the battery and run the electrical parts.
Memory tipBattery starts it, alternator keeps it charged.
Drivetrain
The parts that carry engine power to the wheels: transmission, driveshaft or axles, and the differential, which lets the wheels turn at different speeds in a turn.
Memory tipDifferential = different wheel speeds in turns.
Often tested
- A four-stroke engine cycle: intake, compression, power, exhaust.
- The radiator removes engine heat through the coolant.
- The alternator charges the battery while the engine runs.
- Oil reduces friction between moving engine parts.
- Brake fluid carries pedal force to the wheels.
Easy to confuse: Disc vs. drum brakes
| Part | Disc brake | Drum brake |
|---|---|---|
| Friction part | Brake pads | Brake shoes |
| What it presses on | Rotor (disc) | Inside of a drum |
3 sample questions
Verified practice questions from this unit.
Question 1. What is the correct order of the four strokes in a four-stroke gasoline engine?
- ① Power, intake, exhaust, compression
- ② Compression, intake, exhaust, power
- ③ Intake, power, compression, exhaust
- ④ Intake, compression, power, exhaust
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Answer: ④ Intake, compression, power, exhaust
Key point: Four strokes: intake, compression, power, exhaust
The piston makes four strokes for each cycle. It draws in the air-fuel mixture (intake), squeezes it (compression), the spark ignites it and pushes the piston down (power), and then it pushes the burned gas out (exhaust).
Wrong choices
- (A) Power, intake, exhaust, compression: The cycle starts by drawing in the mixture; burning comes after compression.
- (B) Compression, intake, exhaust, power: The engine must take in air and fuel before it can compress them.
- (C) Intake, power, compression, exhaust: Power cannot come before compression; the mixture must be squeezed before it is ignited.
Question 2. What is the main job of a car's radiator?
- ① To filter dirt out of the engine oil
- ② To remove heat from the engine coolant
- ③ To charge the battery while driving
- ④ To store extra fuel for the engine
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Answer: ② To remove heat from the engine coolant
Key point: Radiator cools the engine coolant
Hot coolant from the engine flows through the radiator's thin tubes and fins. Air passing through the radiator carries the heat away, and the cooled coolant goes back to the engine.
Wrong choices
- (A) To filter dirt out of the engine oil: The oil filter cleans the oil; the radiator handles coolant.
- (C) To charge the battery while driving: The alternator charges the battery.
- (D) To store extra fuel for the engine: Fuel is stored in the fuel tank.
Question 3. While the engine is running, which part produces electricity to recharge the battery?
- ① Voltage gauge
- ② Starter motor
- ③ Distributor
- ④ Alternator
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Answer: ④ Alternator
Key point: Alternator charges the battery
The alternator is turned by a belt from the engine. It makes electricity to recharge the battery and to run the lights, radio, and other electrical parts while the engine runs.
Wrong choices
- (A) Voltage gauge: A gauge only shows a reading; it does not make electricity.
- (B) Starter motor: The starter motor uses battery power to crank the engine; it does not charge the battery.
- (C) Distributor: A distributor sends spark to the cylinders in older engines; it does not produce charging current.