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Cert III Automotive Mechanic study materials
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Cert III Automotive Mechanic practice questions

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Question 1Workplace safety and environmental practices

Which document should a technician consult first to find the correct procedure for safely lifting a vehicle with a two-post hoist?

  1. The parts catalogue for suspension components
  2. The vehicle manufacturer's workshop information and the hoist operating instructions Correct answer.
  3. The tyre placard on the driver's door frame
  4. The workshop's customer invoice template

Explanation

Lifting points are specified by the vehicle manufacturer, while the hoist supplier specifies safe operating limits and procedures. Both sources must be checked before raising a vehicle, because using the wrong jacking point can bend a floor pan or cause the vehicle to fall.

Question 2Workplace safety and environmental practices

What is the main purpose of wearing nitrile gloves when handling used engine oil?

  1. To prevent skin contact with a substance that can cause dermatitis Correct answer.
  2. To stop the oil from oxidising in the container
  3. To keep the hands warm during cold weather
  4. To improve grip on slippery hand tools

Explanation

Used engine oil contains contaminants that can irritate skin and cause dermatitis or more serious harm with repeated exposure. Gloves form a barrier so the oil does not contact the skin, and hands should still be washed after glove removal.

Question 3Workplace safety and environmental practices

A technician must dispose of a small quantity of used brake fluid drained during a repair. What is the correct action?

  1. Tip it onto the gravel outside the workshop
  2. Place it in a sealed container in the designated hazardous waste store Correct answer.
  3. Pour it down the workshop sink with plenty of water
  4. Mix it with used coolant and put it in the general waste bin

Explanation

Brake fluid is a hazardous chemical that must be contained and passed to a licensed waste contractor through the workshop's hazardous waste storage. It must never enter drains, soil or general waste because it is toxic to the environment.

Question 4Workplace safety and environmental practices

Which fire extinguisher type is appropriate for a small fire involving petrol that has spilled from a fuel line?

  1. Carbon dioxide
  2. Water
  3. Wet chemical
  4. Foam (AFFF) Correct answer.

Explanation

Petrol is a Class B flammable liquid fire, and foam blankets the surface to smother the vapour and cool the fuel. Carbon dioxide is also used on flammable liquids, but foam is the standard choice for a spill fire on a flat surface.

Question 5Workplace safety and environmental practices

What does the SDS (Safety Data Sheet) for a workshop chemical tell a technician?

  1. The hazards, safe handling, PPE and first aid measures for the product Correct answer.
  2. The warranty period of the chemical container
  3. The retail price and supplier discount terms
  4. The torque settings for the machine that uses the chemical

Explanation

A Safety Data Sheet is the primary reference for a hazardous chemical, covering its hazards, safe handling and storage, required personal protective equipment, and first aid and spill response. It should be readily accessible to every worker who uses the product.

Question 6Workplace safety and environmental practices

When should a technician report a damaged electrical lead on a workshop power tool?

  1. After the next scheduled tool inspection
  2. Immediately, and remove the tool from service Correct answer.
  3. Only if the tool stops working during use
  4. At the end of the shift during clean-up

Explanation

A damaged lead can cause electric shock or fire, so the tool must be taken out of service at once and tagged to prevent someone else using it. Delaying the report leaves a serious hazard in the workshop.

Question 7Workplace safety and environmental practices

A technician is about to arc weld a bracket on a vehicle. Which combination of controls best manages the main hazards of this task?

  1. Welding helmet with correct shade, leather gloves, fume extraction and fire blanket Correct answer.
  2. Safety glasses, ear plugs and a dust mask
  3. Sunglasses, nitrile gloves and a water spray bottle
  4. Face shield, cotton overalls and a fan blowing fumes toward the doorway

Explanation

Arc welding produces intense ultraviolet radiation, hot spatter and toxic metal fume, so eye and skin protection, fume extraction and fire control are all required. The controls must address each hazard at the same time rather than only one.

Question 8Workplace safety and environmental practices

A trolley jack is being used to raise a vehicle for a wheel removal. What must be done before any part of a person goes under the vehicle?

  1. Lower the jack slightly to settle the load
  2. Chock the wheels and rely on the jack's hydraulic lock
  3. Place axle stands under a rated structural point and lower the jack onto them Correct answer.
  4. Ask a second person to hold the jack handle steady

Explanation

A trolley jack is a lifting device, not a support device, and hydraulics can fail without warning. Axle stands placed under a manufacturer-approved structural point provide a positive support before anyone works beneath the vehicle.

Question 9Workplace safety and environmental practices

A technician spills about two litres of engine oil on the workshop floor. What is the correct order of response?

  1. Spread absorbent over the spill, barricade the area, clean up and dispose of the absorbent as prescribed waste Correct answer.
  2. Hose the area down and allow it to evaporate
  3. Cover the spill with cardboard and continue working
  4. Wash the oil into the floor drain, then mop the area

Explanation

The spill must first be contained and the area made safe for others, then absorbed and cleaned up. Used absorbent is contaminated waste and must go to the correct waste stream rather than a general bin or drain.

Question 10Workplace safety and environmental practices

Why should solvent-based parts wash be kept in a closed container when not in use?

  1. To limit evaporation of volatile vapours into the workshop air Correct answer.
  2. To prevent the solvent from absorbing water
  3. To keep the parts washer looking tidy
  4. To stop the solvent from freezing in winter

Explanation

Solvents release volatile organic compounds that affect indoor air quality and can create a flammable atmosphere. Keeping the lid closed reduces vapour release, odour and fire risk, and it also slows solvent loss.

Question 11Workplace safety and environmental practices

A compressed gas cylinder of oxy-acetylene equipment is to be stored in the workshop. Which practice is correct?

  1. Remove the valve protection caps and leave cylinders free-standing
  2. Store upright, secured with a chain or strap, away from heat and with valves closed Correct answer.
  3. Store them near the parts washer to save space
  4. Lay the cylinders on their side and chain them to a bench

Explanation

Compressed gas cylinders must be stored upright and restrained so they cannot fall, with valves closed and away from ignition sources and heat. Acetylene and oxygen must also be separated in storage according to the supplier's instructions.

Question 12Workplace safety and environmental practices

What is the correct way to handle used oil filters before recycling?

  1. Crush them and put them in the metal scrap bin
  2. Place them in the general waste bin once drained
  3. Wrap them in rags and store them on a shelf
  4. Drain them thoroughly, then place them in the designated used-filter collection container Correct answer.

Explanation

Used oil filters hold residual oil that would contaminate other waste streams, so they are drained and collected separately for recycling. Many jurisdictions regulate filters as a hazardous or controlled waste.

Question 13Workplace safety and environmental practices

A technician notices that a workbench grinder's guard is loose and the tool rest is set too far from the wheel. What is the most appropriate action?

  1. Ask another technician to hold the guard while grinding
  2. Wear a face shield and use the grinder as it is
  3. Use the grinder carefully and adjust it after the task
  4. Adjust the guard and tool rest to the correct clearances before use Correct answer.

Explanation

Guards and tool rests are engineered controls that prevent wheel burst injuries and workpiece jams, and they must be correctly adjusted before the machine is used. The tool rest should sit close to the wheel and the guard should cover the exposed wheel.

Question 14Workplace safety and environmental practices

Which practice best reduces the risk of musculoskeletal injury when removing a heavy gearbox from a vehicle on a hoist?

  1. Hold the gearbox at arm's length to keep it clear of the vehicle
  2. Twist the torso quickly to swing the gearbox clear
  3. Lift the gearbox alone so the task is finished faster
  4. Use a transmission jack or lifting aid and keep the load close to the body Correct answer.

Explanation

Heavy components should be supported by a mechanical aid and handled close to the body to reduce the load on the spine. Twisting and reaching with a heavy load greatly increase the risk of back and shoulder injury.

Question 15Workplace safety and environmental practices

A workshop uses a degreaser that is labelled with a corrosive hazard pictogram. Which set of controls is most appropriate for decanting it into a spray bottle?

  1. Do the decanting near the open workshop door with no PPE
  2. Decant into an unlabelled bottle and store it on the bench
  3. Wear chemical goggles and resistant gloves, use a labelled container and avoid splashing Correct answer.
  4. Wear safety glasses and cotton gloves and decant at eye level

Explanation

Corrosive chemicals can cause severe eye and skin damage, so eye and hand protection plus careful handling are essential. Decanted containers must also be labelled so the contents and hazards remain identifiable.

Question 16Workplace safety and environmental practices

Which action best demonstrates the hierarchy of control when a task produces harmful dust from sanding body filler?

  1. Issue respirators to all technicians and continue the task
  2. Use a sander with dust extraction and enclose the work area, then add respiratory protection Correct answer.
  3. Rotate staff so each person is exposed for only part of the day
  4. Open the workshop doors and rely on natural ventilation

Explanation

The hierarchy of control prefers eliminating or engineering out the hazard before relying on personal protection. Dust extraction and enclosure reduce dust at the source, with respirators used as a final layer rather than the only control.

Question 17Workplace safety and environmental practices

A technician finds an old container in the storeroom with an illegible label and unknown liquid inside. What should be done?

  1. Smell the liquid to identify it, then label the container
  2. Treat it as unknown hazardous waste, keep it closed and report it to the supervisor for identification and disposal Correct answer.
  3. Pour a small amount onto the floor to see how it reacts
  4. Add it to the used coolant drum to save storage space

Explanation

An unidentified chemical cannot be handled safely because its hazards are unknown, so it must remain sealed and be referred to the supervisor for assessment and lawful disposal. Guessing the contents or mixing it with other waste can create dangerous reactions.

Question 18Workplace safety and environmental practices

A workshop's spill kit has been used and not restocked. How does this affect the site's risk controls?

  1. It only matters for large spills above 20 litres
  2. It has no effect because spills are unlikely
  3. It transfers responsibility to the waste contractor
  4. It removes an emergency control, so the risk rating of chemical-handling tasks increases Correct answer.

Explanation

A spill kit is an emergency control that limits the consequences of a foreseeable incident, so an unstocked kit weakens the overall control set. The risk of chemical-handling tasks should be reassessed and the kit restocked before the work continues.

Question 19Workplace safety and environmental practices

Why is it unsafe to use compressed air to blow brake dust from a wheel assembly?

  1. It cools the brake components too quickly
  2. It raises fine particles into the air where they can be inhaled Correct answer.
  3. It damages the brake caliper seals
  4. It increases the tyre pressure

Explanation

Compressed air aerosolises fine dust so it can be breathed in and spread across the workshop, and some brake dust may contain harmful fibres. Dust should be captured with a suitable extraction or wet method and disposed of correctly.

Question 20Workplace safety and environmental practices

A technician must choose between two workshop tasks: one requires working alone under a vehicle after hours, the other requires working alone on a bench job. Which factor most strongly determines the additional controls needed?

  1. The number of tools required for the task
  2. The colour of the vehicle being serviced
  3. The seniority of the technician performing the task
  4. Whether the task can be done without emergency assistance being available Correct answer.

Explanation

Lone work increases risk when an injury could occur and no one is available to raise the alarm, so the ability to summon help is the key factor. Controls such as a check-in system, communication device and restricted tasks address that gap.

Question 21Tools, equipment and workshop hand skills

Which tool is the correct choice for loosening a seized wheel nut without damaging the nut or the wheel stud?

  1. A six-point socket on a breaker bar Correct answer.
  2. A pair of locking pliers
  3. An open-ended spanner
  4. An adjustable wrench

Explanation

A six-point socket grips all flats of the nut evenly, so high torque can be applied without rounding the corners or loading the stud sideways. Breaker bars are designed for this kind of high-leverage loosening. Tools that grip only two faces concentrate stress and slip under load.

Question 22Tools, equipment and workshop hand skills

When using a torque wrench to tighten a cylinder head bolt to a specified setting, what is the correct practice?

  1. Pull smoothly until the wrench clicks or signals, then stop Correct answer.
  2. Add an extension pipe to increase leverage
  3. Use the wrench as a breaker bar to free the bolt first
  4. Store the wrench with the scale set to its maximum

Explanation

A torque wrench signals when the set torque is reached, and the operator should stop applying force at that point. Over-pulling after the signal over-torques the fastener and can stretch it or damage the joint. The tool is a measuring instrument and should not be abused as a breaker bar or lever extension.

Question 23Tools, equipment and workshop hand skills

What is the main purpose of a workshop hydraulic jack and axle stands used together when raising a vehicle?

  1. The stands lift the vehicle and the jack acts as a safety backup
  2. The jack lifts and the stands support the raised vehicle securely Correct answer.
  3. Both devices share the lifting load evenly
  4. The jack holds the load while the stands are only for storage

Explanation

A hydraulic jack is a lifting device only and is not designed to hold a raised vehicle for any length of time. Once the vehicle is at height, axle stands are placed under rated support points to carry the load. This separation of lifting and supporting is the core safe-lifting rule.

Question 24Tools, equipment and workshop hand skills

A technician is measuring the diameter of a valve stem to check for wear. Which measuring tool gives the most accurate reading?

  1. A vernier or digital micrometer Correct answer.
  2. A tape measure
  3. A feeler gauge
  4. A steel rule

Explanation

A micrometer measures small external dimensions to hundredths of a millimetre or better, which suits precision wear checks on components like valve stems. Steel rules and tapes have coarse graduations unsuited to this tolerance. Feeler gauges measure gaps, not diameters.

Question 25Tools, equipment and workshop hand skills

What does a feeler gauge measure when checking valve clearances?

  1. The thickness of the cylinder head gasket
  2. The torque applied to the adjuster
  3. The diameter of the valve stem
  4. The gap between the valve tip and the rocker or cam Correct answer.

Explanation

A feeler gauge is a set of thin blades of known thickness used to check narrow gaps. In valve clearance work the correct blade should slide with slight drag between the valve tip and the rocker or cam lobe base. This confirms the clearance matches specification.

Question 26Tools, equipment and workshop hand skills

Which personal protective equipment is essential when grinding metal on a bench grinder?

  1. Safety glasses or a face shield Correct answer.
  2. A dust mask only
  3. Cotton work gloves
  4. Ear plugs only

Explanation

Grinding throws sparks and metal particles at high speed, so eye and face protection is the primary control. Loose gloves near a rotating wheel are a snag hazard and are generally avoided. Dust and noise controls may also apply but do not replace eye protection.

Question 27Tools, equipment and workshop hand skills

A technician needs to remove a rounded bolt head in a tight space. Which approach is the most appropriate first step?

  1. Apply an open-ended spanner and pull hard
  2. Cut the head off immediately with an oxy torch
  3. Use a dedicated bolt-grip socket designed for rounded heads Correct answer.
  4. Force a smaller socket onto the head with a hammer

Explanation

Bolt-grip sockets have internal flutes that bite into damaged flats and are purpose-made for rounded fasteners. They apply torque to the remaining material rather than the corners. Hammering on an undersized socket or cutting with heat risks further damage and is not a controlled first step.

Question 28Tools, equipment and workshop hand skills

When should a thread tap be used rather than a thread die?

  1. To measure the pitch of an existing thread
  2. To cut internal threads in a drilled hole Correct answer.
  3. To cut external threads on a rod
  4. To remove a broken bolt from a hole

Explanation

Taps cut internal threads inside a hole, while dies cut external threads on the outside of a rod or bolt. They are complementary tools and are chosen by whether the thread is internal or external. Thread pitch is checked with a pitch gauge, and broken bolts are removed with extractors.

Question 29Tools, equipment and workshop hand skills

What is the correct way to care for a precision steel rule to keep its measurements reliable?

  1. Keep it in a toolbox loose with other tools
  2. Oil it heavily and store it standing on end
  3. Use it to pry components apart when needed
  4. Wipe it clean, store it flat, and avoid using it as a scraper Correct answer.

Explanation

A steel rule stays accurate when its edges and graduations are kept clean and unbattered. Storing it flat and reserving it for measuring prevents nicks and wear that shift readings. Using it as a prying or scraping tool damages the edge and ruins accuracy.

Question 30Tools, equipment and workshop hand skills

A technician is choosing a socket for a 12 mm bolt head. What does the socket size number refer to?

  1. The length of the socket in millimetres
  2. The diameter of the drive square
  3. The width across the flats of the fastener it fits Correct answer.
  4. The thread pitch of the bolt

Explanation

Socket sizes are marked as the distance across the flats of the hexagon they engage, matching the fastener head. The drive size, such as 3/8 inch, is a separate specification describing the square drive. Length and thread pitch are unrelated to the socket size marking.

Question 31Tools, equipment and workshop hand skills

Why is a calibrated torque wrench preferable to tightening a critical fastener by feel?

  1. It applies a repeatable, measured torque that matches specification Correct answer.
  2. It prevents the fastener from ever loosening
  3. It always tightens faster than hand tools
  4. It removes the need for any specification

Explanation

Critical joints such as cylinder heads and suspension components depend on a specified clamping load. A calibrated torque wrench delivers that load repeatably, whereas feel varies between people and sessions. It does not guarantee against loosening or replace specifications.

Question 32Tools, equipment and workshop hand skills

What is the purpose of a puller when removing a wheel bearing or pulley?

  1. To heat the component for expansion
  2. To draw the component off its shaft with controlled axial force Correct answer.
  3. To measure the bearing preload
  4. To cut the bearing race free

Explanation

A puller uses a central screw and jaws or legs to apply controlled axial force, drawing a press-fit component off a shaft without hammering. This protects the shaft and the component from impact damage. It does not cut, heat, or measure anything.

Question 33Tools, equipment and workshop hand skills

A technician notices the handle of a ball-peen hammer is cracked near the head. What is the correct action?

  1. Use the hammer only for light taps
  2. Remove the hammer from service and replace the handle or hammer Correct answer.
  3. Wrap the handle with tape and continue
  4. Shorten the handle to remove the crack

Explanation

A cracked handle can fail under impact and send the head flying, which is a serious injury risk. Damaged striking tools must be taken out of service and repaired or replaced. Taping or restricting use does not restore structural integrity.

Question 34Tools, equipment and workshop hand skills

When using a bench vice to hold a workpiece for filing, what is good practice?

  1. Clamp the work close to the jaws and use soft jaws for finished surfaces Correct answer.
  2. Tighten the vice as hard as possible on any surface
  3. Leave the vice slightly loose so the work can move
  4. Hold the work at the outer edge of the jaws

Explanation

Work held low and close to the jaws is supported rigidly, reducing vibration and jaw strain. Soft jaws or pads protect machined or finished surfaces from jaw marks. Over-tightening or holding at the jaw tips risks damage and poor control.

Question 35Tools, equipment and workshop hand skills

Which instrument is used to check that a cylinder bore is not worn oval or tapered?

  1. A dial test indicator on a magnetic base
  2. A vernier caliper
  3. A bore gauge Correct answer.
  4. A depth micrometer

Explanation

A bore gauge measures internal diameter at different heights and orientations, revealing ovality and taper in a cylinder. Calipers measure outside and inside dimensions but lack the reach and precision for bore wear mapping. Depth micrometers and dial indicators measure other features.

Question 36Tools, equipment and workshop hand skills

A technician must loosen a very tight suspension bolt. Which combination is safest and most effective?

  1. A twelve-point socket on a ratchet with an extension pipe
  2. A screwdriver wedged into the bolt head
  3. An open-ended spanner with a hammer strike
  4. A six-point impact socket on a breaker bar with the vehicle stable Correct answer.

Explanation

A six-point impact socket spreads load across the flats and resists splitting under high torque, and a breaker bar provides controlled leverage. The vehicle must be stable and supported before force is applied. Twelve-point sockets and improvised levers increase the risk of slipping or breaking tools.

Question 37Tools, equipment and workshop hand skills

What is the main reason for using a torque angle gauge after reaching a preliminary torque on some modern head bolts?

  1. To apply a controlled additional rotation that stretches the bolt to its designed clamp load Correct answer.
  2. To measure the final torque directly in newton metres
  3. To check that the bolt thread pitch is correct
  4. To confirm the bolt has not been over-tightened

Explanation

Torque-to-yield bolts are designed to stretch within their elastic range, and the final clamp load is set by a specified angle of rotation after a low initial torque. The angle method is more consistent than torque alone because friction varies. It is not a direct torque measurement.

Question 38Tools, equipment and workshop hand skills

When should a technician use a tap wrench rather than a standard ratchet to drive a tap?

  1. When cutting threads by hand and needing even, controlled force with feel Correct answer.
  2. When the tap is being driven by a power drill
  3. When the hole is being reamed to size
  4. When the thread is being rolled rather than cut

Explanation

A tap wrench applies torque symmetrically through two handles, letting the operator feel the cut and reverse to break chips. This control reduces the risk of snapping a tap in the hole. Power drilling and reaming are different operations with different tooling.

Question 39Tools, equipment and workshop hand skills

A dial test indicator reads 0.05 mm runout on a brake disc. What does this measurement indicate?

  1. The disc has been machined to the wrong diameter
  2. The disc thickness is 0.05 mm below specification
  3. The disc surface varies in height as it rotates, which may cause vibration Correct answer.
  4. The wheel bearing preload is correct

Explanation

A dial test indicator measures small displacements as a part rotates, so a runout reading shows how far the surface moves axially or radially. On a brake disc this lateral variation can produce pedal pulsation or vibration. It does not measure thickness or diameter.

Question 40Tools, equipment and workshop hand skills

What is the correct procedure for safely using an angle grinder to dress a weld on a bench?

  1. Remove the guard for better access and work without glasses
  2. Secure the work, fit the guard, wear eye and face protection, and keep the disc clear of the body Correct answer.
  3. Hold the work by hand and grind toward yourself
  4. Use a cutting disc for all grinding tasks

Explanation

An angle grinder throws high-speed fragments, so the guard, eye and face protection, and a secure workpiece are essential controls. The tool should be held so sparks travel away from the operator. Removing guards or using the wrong disc type defeats these protections.

Question 41Engine mechanical systems diagnosis and repair

Which component drives the camshaft on a pushrod engine with the cam located in the block?

  1. The starter motor pinion
  2. The oil pump driveshaft
  3. The flywheel ring gear
  4. The timing chain or belt from the crankshaft Correct answer.

Explanation

In a block-mounted cam engine the camshaft is driven at half crankshaft speed by a chain, belt, or gear train connected to the crankshaft. This maintains correct valve timing relative to piston position. The oil pump may be driven by the cam, not the reverse.

Question 42Engine mechanical systems diagnosis and repair

A four-stroke engine completes one full cycle in how many crankshaft revolutions?

  1. Eight
  2. One
  3. Two Correct answer.
  4. Four

Explanation

A four-stroke cycle requires intake, compression, power, and exhaust strokes, which together take two full crankshaft revolutions. The camshaft turns only once during that period because it is driven at half crank speed.

Question 43Engine mechanical systems diagnosis and repair

What is the primary purpose of valve clearance (lash) on a mechanical valvetrain?

  1. To reduce oil pressure at the camshaft bearings
  2. To allow for thermal expansion so valves fully seat when hot Correct answer.
  3. To hold the valve spring retainer in place
  4. To increase valve lift at high engine speed

Explanation

Mechanical valvetrains need a small gap because components expand as the engine warms. Without clearance the valve may be held slightly off its seat when hot, causing compression loss and burned valves. The gap is set to the manufacturer's specification when the engine is cold or hot as stated.

Question 44Engine mechanical systems diagnosis and repair

Which test best confirms a suspected blown head gasket between two adjacent cylinders?

  1. A cylinder leakage test showing air escaping into the neighbouring cylinder Correct answer.
  2. A fuel pressure drop test
  3. A wheel alignment check
  4. A charging system voltage test

Explanation

Air introduced into one cylinder during a leakage test normally escapes past rings, valves, or into the cooling system. Bubbling or airflow heard at the adjacent cylinder's spark plug hole indicates a breach in the head gasket fire ring between those bores. This isolates the fault to the gasket rather than rings or valves.

Question 45Engine mechanical systems diagnosis and repair

During a compression test, one cylinder reads much lower than the others, but adding oil raises the reading significantly. What does this indicate?

  1. A leaking head gasket
  2. Worn piston rings or cylinder bore Correct answer.
  3. A jumped timing chain
  4. A burned exhaust valve

Explanation

Oil temporarily seals the gap between rings and cylinder wall, so a wet reading that rises sharply points to ring or bore wear. If the low reading persists after oiling, the leak is more likely at a valve or gasket. This wet/dry comparison is the standard way to localise compression loss.

Question 46Engine mechanical systems diagnosis and repair

What is the function of a thermostat in an engine cooling system?

  1. To cool the engine oil in the sump
  2. To circulate coolant through the radiator
  3. To detect coolant level in the expansion tank
  4. To regulate coolant flow and maintain operating temperature Correct answer.

Explanation

The thermostat opens and closes with temperature to control coolant flow to the radiator. This keeps the engine within its designed operating range for efficiency, emissions, and wear control. It does not pump coolant or sense level.

Question 47Engine mechanical systems diagnosis and repair

Which symptom most directly indicates excessive valve lash on one cylinder of a mechanical valvetrain?

  1. A steady drop in fuel pressure
  2. Continuous blue exhaust smoke
  3. A grinding noise from the starter
  4. A rhythmic ticking noise from the top of that cylinder Correct answer.

Explanation

Excessive clearance allows the rocker or cam follower to strike the valve tip, producing a rhythmic tick at half crank speed. The noise location follows the affected cylinder. Blue smoke, fuel pressure, and starter noise relate to other systems.

Question 48Engine mechanical systems diagnosis and repair

What does the term 'valve overlap' describe?

  1. The clearance between valve stem and guide
  2. The distance the valve spring is compressed
  3. A period when intake and exhaust valves are both open near top dead centre Correct answer.
  4. The angle between two camshaft lobes

Explanation

Overlap occurs when the intake valve has opened before the exhaust valve fully closes, around the end of the exhaust stroke. It helps scavenge exhaust gases and improve cylinder filling at speed. Overlap is set by camshaft design and timing.

Question 49Engine mechanical systems diagnosis and repair

A vehicle has a persistent misfire on cylinder 3. A compression test is normal, spark is confirmed, and swapping the coil and injector does not move the misfire. Which step is most appropriate next?

  1. Perform a cylinder leakage test and inspect valve action on cylinder 3 Correct answer.
  2. Replace all four ignition coils
  3. Replace the engine control module
  4. Drain and replace the engine oil

Explanation

With spark and fuel already ruled out by substitution and compression normal, a mechanical fault such as a sticking valve, worn cam lobe, or leaking valve seat remains possible. A leakage test and visual inspection of valve movement will confirm or exclude these. Replacing the ECU is premature without further diagnosis.

Question 50Engine mechanical systems diagnosis and repair

Which condition would cause a timing belt to jump teeth and upset valve timing?

  1. A weak fuel pump
  2. A clogged air filter
  3. An overcharged battery
  4. A worn or failed automatic tensioner Correct answer.

Explanation

The tensioner maintains belt tension as the engine expands and the belt stretches. A worn or failed tensioner allows slack, so the belt can jump on the cam sprocket and shift valve timing. Air, fuel, and charging faults do not affect belt position.