The ultimate guide to car parts and what they do - with pictures

Many drivers who love getting behind the wheel still have no idea what’s going on under the hood.

To help bring you up to speed, here’s our ultimate guide to essential car parts in a manual, fuel-powered car. Find out what they do, how they can go wrong and whether you should attempt fixing them yourself.

Jump to:

Battery
Distributor
Alternator
Radiator
Thermostat
Spark plug
Ignition coil
Tyres
Spare tyre
Shock absorbers
Brakes
Air filter
Catalytic converter
Clutch
Gearbox
Water pump
Air conditioning compressor

Battery

What is a car battery?

A critically-important part of your car’s electrical system, the battery starts the engine when you turn the key in the ignition. It provides a back-up source of power for in-car electronics should the alternator need help.

Car battery problems

Unfortunately, plenty can go wrong with a battery, so it’s a good idea to know what to do should the worst happen.

If your car won’t start, it could mean your battery’s flat. Jump start your engine from either another vehicle or an engine jump starter, and your battery will then recharge during the journey. The longer the journey, the more recharge.

If your engine still won’t start, there could be a more serious problem with your battery, from sulfation (which will come with a nasty sulphur smell) to corrosion, which will mean you’ll need to buy a new battery.

Experts recommend replacing your car battery somewhere between every two to five years, but if yours is prone to losing charge you may want to invest in a charger to keep your vehicle on the road.

Can I fix a car battery myself?

You won’t be able to fix a battery yourself but you’ll be able to charge or jump-start a battery low on charge or buy a replacement if it’s corroded or faulty.

For a flat battery: Here’s a video guide to jump starting your car.

For a battery replacement: Enter your reg here to find the right battery for your car.

Not sure: If you need assistance you can call the RAC on 03301 598 751 whether you are a member or not. 

Or: Find a garage.

Distributor

What is a car distributor?

They direct high voltage from the ignition coil to the spark plugs as and when needed. Although many modern cars don’t actually have distributors, for those that do they’re a key component of the ignition process.

Car distributor problems

As well as general wear, the most likely thing that’ll go wrong is a build-up of dirt and other engine sludge in the distributor cap causing faults. Make sure you clean it regularly.

Can I fix a car distributor myself?

It might be that just your distributor cap needs fixing, which is easily done. However, mechanics recommend changing both distributor cap and rotor at the same time regardless of condition.

Alternator

What is a car alternator?

While the battery takes care of actually starting your engine, the alternator powers all the other electronics that keep your car running like headlights and windscreen wipers. Your alternator also keeps the car battery charged.

Car alternator problems:

Perhaps unsurprisingly considering its importance, quite a lot can go wrong with an alternator. A dead one will mean the battery warning light comes on, the engine eventually stalls, and your car dies – bad news.

Unfortunately, it’s likely you won’t get much warning that your alternator is about to crash out, but thankfully it’s often a single component of the alternator that goes, so you don’t have to replace the entire thing.

Problems in the alternator include worn or loose belts, broken or failed bearings and faulty pulleys. You should expect to change your alternator every 40,000 to 100,000 miles to ensure it keeps working properly.

Can I fix a car alternator myself?

Replacing an entire alternator means a few loosened screws and replaced connections, however an alternator’s position may make an easy job trickier and you may prefer taking it to a garage.

Radiator

What is a car radiator?

An integral part of your engine’s cooling system, the radiator prevents your car from overheating by cooling down hot coolant coming from the engine, before sending it back in.  

Car radiator problems

Happily, radiators tend to last around a decade on average. That doesn’t mean you’ll definitely be free of problems though as leaking, rusting, overheating and mineral deposits can all leave them with faults.

If your temperature gauge is showing a high temperature or if coolant is leaking onto the ground beneath your vehicle, it could be a sign there’s an issue with your radiator that needs to be taken care of.

Can I fix a car radiator myself?

That depends. If you’re simply running low on coolant, then top it up - watch our video guide to find out how. Grab some coolant here if you haven’t got any handy.

However, if your radiator is leaking, often the best way to fix it is to simply replace it with a new one and that’ll require a professional, so find a local garage.

• How to check your engine coolant
• Why is my car making that noise? A guide to unusual vehicle sounds
• How to do a three-point turn — driving guide

Thermostat

What is a car thermostat?

Just like your thermostat at home, the one in your car helps regulate the temperature of your engine, managing the flow of coolant as needed to let your engine warm up faster or cool down if it’s overheating.

Car thermostat problems

There’s usually two things that go wrong with thermostats – they either get stuck in the open position or they get stuck in the closed position.

You’ll notice a thermometer stuck in the closed position much quicker, as the temperature gauge in your car will quickly run into red and you could damage your engine in a matter of minutes if you keep driving.

Whatever’s wrong with your thermometer you’ll need to replace it as soon as possible as you won’t want to drive anywhere with a faulty thermometer even if an initial inspection doesn’t look too bad.

If you need assistance you can call the RAC on 03301 598 751 whether you are a member or not.

Can I fix a car thermostat myself?

Yes, but avoid burns by ensuring your engine is completely cooled beforehand and be sure to clean the area thoroughly before replacing it to ensure it doesn’t get stuck again.

Spark plug

What is a spark plug?

A spark plug is part of your car’s ignition system – providing the spark that sets off the combustion in the engine which allows your car to move.

Spark plug problems

A well-used part of your car, spark plugs take a lot of wear and tear and the electrodes in the plugs will become damages over time. As a rule of thumb, mechanics suggest replacing them every 30,000 miles.

Spark plugs will also suffer if there’s any oil leaks in your engine, so if they start to fail well before the 30,000-mile mark, it could be a sign that there’s another underlying issue.

Can I fix a spark plug myself?

If you’ve got the right tools – including a torque wrench, spark plug socket spanner, feeler blades and, of course, new spark plugs – you should be able to replace your spark plugs yourself.

Remove the HT leads first and after unscrewing the plugs, clean the area thoroughly. Check the electrode gap of the new plugs using the feeler blades before preparing them and screwing them back in.

Not confident that you can do it yourself? You’re not alone, find an RAC approved garage near you now.

Ignition coil

What is an ignition coil?

Another important part of your car’s ignition system, the ignition coil supplies the high voltage (around 30,000 volts) the spark plugs in your engine need to create a spark.

Ignition coil problems

If your car backfires or stalls a lot, it could be a sign your ignition coil is faulty and causing your spark plugs to ignite irregularly.

Like spark plugs, ignition coils are susceptible to general wear and tear, although with mechanics only recommending a new ignition coil every 100,000 miles, a faulty one could signal damage caused by leaking fluids in the engine.

Can I fix an ignition coil myself?

Yes, it’s simply a matter of removing the old coils and installing new ones – just don’t forget to install the new coil in the reverse order you disconnected the old one to ensure everything works OK.

Check out our RAC approved garage network if you’d rather leave it to a professional.

Tyres

What are tyres?

Your cars tyres are the rubber, inflated rings that encircle your wheels. They’re the only point of contact your car has with the road and from sharp cornering to the plague of potholes, they put up with a lot on a day-to-day basis so you should look after them.

Tyre problems

The entire weight of your car is supported by the air pressure in your tyres, and experts predict poorly maintained tyres could end up costing you around 3% in terms of mileage per tank efficiency. 

A flat tyre or a blow-out could be even more serious but can be avoided if you properly maintain your tyres and get them replaced when you see signs of wear and tear. Make sure you always have a fully-functioning spare just in case you need it.

Can I fix tyres myself?

Changing a tyre can be fairly straightforward providing you know what you’re doing. Follow these 10 simple steps on how to change a tyre and you’ll be back on the road in no time.

Not so confident? Enter your reg here to find the right tyres for your car, then choose a local garage to fit them for you.

All RAC patrols carry the RAC Universal Spare Wheel - a multi-fit wheel designed to get you back on the move fast.

Need assistance now? Call the RAC on 03301 598 751 whether you are a member or not.

Spare tyre

What is a spare tyre?

Usually stowed in your car’s boot, a spare tyre is either a full-size or compact additional tyre that’s carried in case one of your tyres goes flat or bursts and you need an immediate replacement.

Spare tyre problems

If you’re using a compact spare, most manufacturers recommend you only drive limited distances and at speeds below 50mph, as these tyres aren’t designed for prolonged use.

Once you’ve used your spare, you should replace it as soon as possible to ensure you have a fully-functioning replacement should you suffer another flat or blow out on the road.

Can I fix a spare tyre myself?

Getting hold of a replacement spare tyre is fairly easy, and you should be able to pick one up at your local garage or auto parts shop.

Shock absorbers

What are shock absorbers?

An important part of your suspension, shock absorbers do what their name suggests: they absorb shock from your tyres, ensuring they stay on the ground and provide a comfortable driving experience.

Shock absorber problems

If your car vibrates while driving or swerves dangerously under braking, you could have problems with your shock absorbers and need to get them sorted as soon as possible.

These issues could relate to something simple like general wear and tear, or could be a symptom of a ruptured seal or leak within the shock absorber itself.

Can I fix shock absorbers myself?

While it might be possible to repair faulty shock absorbers, mechanics recommend replacing all four at once to ensure your vehicle maintains the right balance.

Replacing all four shocks isn’t the easiest task in the world but it is possible with the right tools, just remember to properly support the axle with a jack to stop the shock from shooting downwards and injuring you.

To avoid the risk, get a professional to take a look for you.

Brakes

What are brakes?

Clearly among the most important safety features, brakes slow your vehicle or bring it to a stop when pressure is applied to the brake pedal.

Brake problems

There are plenty. A typical braking system is made up of a brake disc (or rotor), a brake calliper and a pair of brake pads. As most modern cars have brakes on all four wheels there are a number of parts that could fail.

Problems with your brakes could range from something simple, like running out of brake fluid, to a failed brake rotor that could see your car pulling towards one side of the road or burned-through brake pads.

The most common problem with your braking system is likely to come from your brake pads, which mechanics recommend changing every 25,000 miles – although they have been known to need replacing after just 15,000 miles.

However, the lifespan of your brake components will depend largely on where and how you drive, with an aggressive urban driver likely to put much more strain on their brake parts than a more relaxed, rural motorist.

Can I fix brakes myself?

That depends what’s wrong with them. If you’re running low on brake fluid then it’s simple to top up, while with some standard tools (like a jack and a socket spanner) you’ll be able to replace brake pads.

However, if it’s something more serious at fault, you may want to check your car into a garage. Brakes are essential safety features and you could be putting yourself and others at risk if your braking system isn’t working.

Air filter

What is an engine air filter?

Your engine’s air filter prevents any debris or dirt getting into it and shouldn’t be confused with the cabin’s air filter, which stops dust or pollen from entering the cabin through the A/C and heat vents.

Engine air filter problems

Over time, air filters become clogged with dust and dirt and a clogged filter can lead to a number of tell-tale signs, including reduced fuel economy, unusual engine sounds and black smoke from the exhaust pipe.

On average, an air filter will last around 30,000 miles or three years (whichever comes first) before needing to be replaced, although if you spend a lot of time on dirt tracks then this could drop to a lifespan of as little as 6,000 miles.

Can I fix an engine air filter myself?

Yes, changing an air filter is simply a matter of removing the old filter from the engine, cleaning out the area, and replacing it with a brand-new filter — just make sure you have the right one for your car.   

Catalytic converter

What is a catalytic converter?

Catalytic converters (or “cats”) essentially clean up your car’s exhaust fumes, greatly reducing the harmful hydrocarbons, carbon monoxide, and nitrogen oxide your car releases into the atmosphere via its exhaust pipe.

Catalytic converter problems

Over time, the build-up of carbon deposits inside your cat can cause blockages, restricting the flow of gases passing through the exhaust and affecting your engine’s efficiency.

This can be seen by reduced acceleration and sluggish engine performance; however most modern cars have on-board diagnostic systems which mean a warning light will flash up on your dashboard when you have problems.

Can I fix a catalytic converter myself?

Aim to clean out your catalytic converter regularly to maintain its functionality – this can be done at home with a DIY fuel system cleaner.

Cats are expensive due to the precious metals used in making them, but you shouldn’t skimp on replacing them, so get them checked regularly and ensure you don’t fall foul of any avoidable damage.

Clutch

What is a clutch?

The clutch connects the engine and transmission, and ensures a car moves smoothly through the gears. It’s a part of both manual and automatic cars.

Clutch problems

If your clutch starts ‘slipping’ (i.e. causing a momentary loss of acceleration), squeaking or the clutch pedal feels spongy when pressed, that probably means you’ve got problems.

In an automatic car, clutch issues usually relate to worn out clutch discs and pressure plates, which experts estimate should last between five and seven years, but there are more potential issues with a manual transmission.  

Other problems include a cracked or bent flywheel (the part of the clutch which connects to the engine) or a leaking master or slave cylinder if you have a hydraulic clutch.

Can I fix a clutch myself?

Yes, although it can be quite a laborious task even if you know what you’re doing, as you’ll likely need to remove the driveshaft, bell housing and gearbox from underneath your vehicle.

Once you’ve done all that, you’ll have to unbolt the clutch from the flywheel to replace it and you may want to replace the flywheel, too, if you notice any contamination or warping.

As there are so many mission-critical moving parts involved in the replacement of a clutch, most people rely on a garage to deal with their clutch issues.

A dodgy clutch is one of the most common reasons for a breakdown, so if you’re in need of assistance right now call the RAC on 03301 598 751 whether you are a member or not.

Gearbox

What is a gearbox?

Also known as the transmission, the gearbox transmits the power generated by the engine to the wheels, allowing them to move.

Gearbox problems:

These largely depend on what kind of transmission you have — manual or automatic being the most common — but generally they relate to worn out gears or issues with your transmission fluid.

If fluid is the issue, it could mean you’re running low or have a leak. If you don’t change your fluid regularly enough, this could also lead to a clogged transmission line, which can also cause problems.

Can I fix a gearbox myself?

As a rule of thumb, transmission fluid needs changing every 30,000 miles, and after 100,000 it’s likely you’ll need to check your motor in with a garage for a complete transmission replacement due to wear and tear.  

More likely, you’ll need to simply replace a single component of your gearbox, although transmissions can be one of the more challenging DIY mechanic jobs out there, so you might want to leave it to the professionals.

• Regular car checks to help prevent a breakdown and keep you safe
• Help! My car won’t start, what do I do?
• 7 things you should never do when driving a manual

Water pump

What is a car water pump?

Part of your engine’s cooling system, a water pump helps circulate the coolant between the engine (where it absorbs heat) and the radiator (where it lets heat go).

Car water pump problems

Whether mechanical or electrical, water pumps are prone to failure. Electronic pumps are notorious for dying without warning, while mechanical pumps will often give you some warning they’re on their way out.

This could be from a seal cracking or breaking, a worn-out timing belt, or the water pump impeller rusting. Any of these issues will mean you’re going to need a whole new pump and a fresh tank of coolant to get you back on the road.

Can I fix a car water pump myself?

Experts say a pump’s timing belt should last around 100,000 miles so you might never need to fix your water pump. If you do, it’s advisable to replace the entire pump instead of trying to just fix parts.

Replacing a pump is a fairly simple process if you’re confident under the bonnet, just remember to clean the area thoroughly with cleaning solution before fixing the new pump and making sure you reconnect everything you disconnect.  

Air conditioning compressor

What is an air conditioning compressor?

The air-con compressor is an integral part of the air-conditioning system, compressing the coolant before it goes into the condenser and helping to cool down your cabin.

Air conditioning compressor problems:

If you’ve got issues with your A/C system, it’s likely to be a leak. However, if there isn’t a leak, it could mean your compressor isn’t working.

Unfortunately, there are a number of things that could go wrong with your compressor – from a broken seal to a failing mechanism – and these issues will likely mean you need a whole new compressor unit.

Can I fix an air conditioning compressor myself?

The good news is A/C compressors typically last the lifetime of a car. The bad news is it can be one of the trickier things to fix yourself, so it’s best to let a professional at a garage take care of it.