Car Care and Maintenance Glossary

Whether you’re a passionate driveway DIY-er or a recent trip to a mechanic has left you baffled, our car care and maintenance glossary can help you brush up on your knowledge of common car maintenance terms, and diagnose underlying problems.

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Air Filter

Mounted in the air intake system, air filters catch dirt, dust and debris which could damage the engine or reduce performance. Air filters are disposable and should be replaced in line with the service schedule recommended by the manufacturer.

Aircon Odour Bomb

Holts Aircon Odour Bomb can be used to deodorise your car’s air-conditioning system, neutralising unpleasant odours caused by a build-up of dust and dirt in the system. 


An electricity generator which provides power to the ignition system and electronics. The alternator is powered by a belt and pulley system and will stop working if the drive belt breaks. Signs of a failing alternator include dim headlights and a low or flat battery. 

Anti-Lock Braking System (ABS)

An electronic braking system that detects when a wheel has locked up, and automatically reduces the braking force to keep the wheel rolling, preventing a skid.

Automatic Transmission Fluid

Automatic transmission fluid cools the transmission system and lubricates moving parts in automatic cars. Make sure your car’s transmission fluid level is always up to ‘full’ on the reservoir, without overfilling.


See coolant/antifreeze


Bradex Easy Start

Bradex Easy Start can be used to help your car start. Sprayed directly into the air intake, it makes the fuel/air mix more combustible, so the engine fires more readily. Ideal for cold mornings, Bradex Easy Start is suitable for both petrol and diesel engines. 

Brake Fluid

The fluid used in a car’s hydraulic brake system. Brake fluid is used to transfer pressure through the brake lines to the wheels. As a hygroscopic chemical, brake fluid absorbs moisture which can inhibit braking performance. Ensure you follow the replacement service schedule recommended by the manufacturer, usually two years.

Brake Lines and Hoses

The tubes and connectors which carry brake fluid through the brake system, transferring braking forces to the wheels.

Brake Pads

A type of high-friction material used in disc and drum brakes. Brake pads provide stopping power to the wheel while helping to limit wear. Brake pads should be checked regularly and replaced when worn.

Brake Assist

An active braking system that helps with emergency braking, usually working in combination with the ABS to ensure effective braking while avoiding wheel lock.



A carburettor is used to blend the air and fuel mix in an engine to create the correct ratio for combustion. Carburettors have been replaced by fuel injectors, but are still found in older cars and machines with a small engine, such as lawnmowers.

Catalytic Converter

A catalytic converter is an emissions control device used in a car’s exhaust system to convert toxic gases emitted from an engine into less harmful pollutants.

Catalytic Converter Heat Shield

This is a metal cover used to protect components from the heat of the catalytic converter and exhaust pipe. Loose heat shielding is a common problem, particularly on older cars. 


The fluid used to keep the engine operating at the right temperature. This is usually a mixture of water and ethylene glycol, circulated through the engine bay via the cooling system. It transfers excess heat away from the engine, and prevents freezing in cold temperatures. These fluid should also protect the cooling system from corrosion.

Cooling Fan

The mechanical or electrically operated fan used to pull air into the vehicle’s radiator, helping to cool the coolant/antifreeze fluid inside the cooling system and maintain the engine at the correct operating temperature.


Diesel Particulate Filter (DPF)

A device used to remove soot and particles from the exhaust emissions of a diesel engine. The main job of a DPF is to control the particulate emissions of a diesel car.


A device used to check engine oil and automatic transmission fluid levels.


The drivetrain is a term for the components that make a car move, including the wheels, transmission, engine and clutch assembly.

Drive Belt

A strong rubber belt which utilises the rotation of the engine’s crankshaft, sending power to components such as the water pump, alternator, air conditioning compressor, supercharger or power-steering pump. Sometimes known as auxiliary belt.


ECU (Engine Control Unit)

The ECU controls all elements of the engine to ensure optimum performance. Using a series of sensors, the ECU interprets data and uses it to control air/fuel mix, valve timing and more. It also monitors the emissions from the exhaust system and can sense when a problem has occurred. The check engine light is illuminated when the ECU has discovered a problem. 

Engine Oil

A fluid that lubricates all moving parts within the engine, reducing wear whilst allowing components to move freely. The engine oil level can be checked using a dipstick, and should be changed in line with the service schedule recommended by the manufacturer to extend the life of the engine.

Engine Thermostat

The engine thermostat regulates the cooling of the engine. At a specified temperature it opens to allow the coolant to flow through the radiator, this reduces the temperature of the coolant. If this fails whilst closed it can cause overheating, and if it fails whilst open the engine coolant will often run at a lower temperature than normal.

Exhaust Manifold

The exhaust manifold connects directly to the engine, funnelling heat and exhaust gases through the exhaust system, into the catalytic converter, and out towards the rear of the car. A faulty exhaust manifold can be dangerous, as poisonous gases such as carbon monoxide can leak, posing a risk to those inside the car.


Fan Belt

The rubber belt used to control the cooling fan in vehicles with a mechanical cooling fan.


Holts Firegum is an exhaust assembly paste which offers a gas-tight seal when assembling an exhaust system.

Fuel Filter

A replaceable metal or plastic filter which prevents particles and contaminants in the fuel tank from reaching the engine.

Fuel Pump

A small pump which sends the fuel from the tank to the engine. This is usually found in the fuel tank itself, and is electrically-powered on most modern cars. 

Fuel Pump Shut-Off

A pump that automatically shuts the flow of fuel to the engine after a collision.


Glow Plug

Diesel engines compress the air in the combustion chamber, this increases the temperature. When diesel fuel is then injected into the combustion chamber it ignites spontaneously.  In cold weather the ignition temperature isn’t always reached at start up. Glow plugs help achieve the correct temperature by warming the air in the combustion chamber during cold starting.   

Gun Gum

Gun Gum is a range of exhaust repair products, which can be used to fill holes and cracks in an exhaust system. The Holts Gun Gum range includes an easy-to-use paste, as well as bandages and wraps for those hard-to-reach areas.


Head Gasket

The head gasket provides a seal between the cylinder head and the engine block..

Heater Core

The heater core is a small radiator unit which transfers heat from the engine into the cabin. This component is located close to the bulkhead, and is part of the cooling system for the engine.


Ignition Coil

The ignition coil is used to convert power from the low voltage systems used throughout the vehicle into the 10,000V spark needed for an effective ignition in petrol vehicles. 

Ignition Timing

Controlled by the ECU, ignition timing refers to the exact point at which a spark should occur in the combustion chamber, triggering ignition. This is relative to the crankshaft speed and the position of the pistons.


Maintenance Spray

A multi-purpose product that lubricates moving parts, and protects them from rust and corrosion. 

Manual Transmission Fluid

The fluid used in a manual transmission system, to lubricate and cool moving parts.

MPG (Miles Per Gallon)

The number of miles that can be achieved for every gallon of fuel, available as a real-time figure, per tank, or over the lifetime of the vehicle.


OEM (Original Equipment Manufacturer)

A term used to categorise components built by the vehicle’s original manufacturer. E.G. an original Ford air filter fitted to a Ford car.

Oil Filter

A small cartridge-style filter fitted to an engine’s lubricating system, and used to remove particles, dirt and abrasive matter from the engine oil.

Oil Pump

A pump used to move engine oil through the engine internals, lubricating moving parts.

Oil Pan

The oil pan is where the engine oil is stored and from where the pump feeds it through the engine. The pump forces oil from the oil pan, through the filter, and around the engine. The engine oil dipstick extends down into the oil pan, to measure its level. There’s also a plug on the bottom of the pan for draining off the oil when it’s ready for changing. It’s also known as the sump.

Overheated Engine

An overheated engine occurs when the engine goes above its normal operating temperature, causing metal components to heat up, expand and cause friction. Severe overheating can even cause the flat surfaces in the engine to warp, meaning they fail to seal together. Many things can cause an engine to overheat, including a leak in the cooling system, a broken or faulty fan belt/auxiliary belt a faulty electric fan, blocked radiator, or even a radiator or coolant/antifreeze cap that isn’t securely tightened.


Power Steering Fluid

The fluid in the hydraulic system which is used to reduce the physical effort of turning the steering wheel.



The radiator is the main part of a car’s cooling system. It ensures the engine maintains an optimum working temperature. It sits at the front of the car, and is used to continuously dissipate heat from the coolant/antifreeze mix circulating through the engine. 

Radiator/Cooling Fan

The radiator/cooling fan draws air through the front grille of the car and into the radiator, where it helps to cool the coolant/antifreeze in the cooling system.


Holts Radweld is a radiator cooling system leak repair, which seals leaks in the cooling system, including small holes in radiators and hoses. Radweld Plus is an additional product in the range which acts as a total cooling system repair, sealing leaks in radiators, engine blocks, cylinder heads and hoses.

Rotate Tyres

Rotating tyres is a process which prevents tyres at the front of the car from wearing faster than those at the rear, for even and balanced tread wear. To rotate the tyres, you should move the front driver-side tyre to the rear passenger-side position, and the front passenger-side tyre to the driver-side position. Some manufacturers recommend rotating tyres every 6 to 12 months, depending on your mileage.

Run Flat

A tyre with a reinforced sidewall or supportive foam band that ensures the tyre isn’t damaged when it’s partially deflated.


Shock Absorber

Forming part of the suspension system, the shock absorber controls the up and down motion of a vehicle’s wheels. Also called ‘dampers’ or ‘suspension struts’, shock absorbers reduce the excessive up and down movements, keeping the car’s body steady on the road.

Spark Plug

Spark plugs create the spark needed to ignite the petrol/air mixture in the combustion chamber. These sit in the engine cylinder, and create a spark in excess of 10,000V to ignite the engine.


Holts Speedflush is a cooling system cleaner that removes harmful scale and deposits from the engine, extending the life of components within the system and preventing problems like blockages.


The starter is a small electric motor that uses power from the battery to turn the crankshaft via the flywheel and start the engine.

Steering Rack

The steering rack connects the two front wheels, and is part of a rack-and-pinion steering system. Parallel to the front axle, the steering rack moves left and right as the wheels turn, and are expected to last for the lifetime of the vehicle.


Timing Belt Tensioner

An idler wheel that keeps the timing belt under tension, preventing it from going out of sync.

Traction Control

An active control system that monitors and regulates the speed at which the wheels are spinning, allowing it to measure when a wheel is spinning too fast and is liable to skid. The traction control system controls the brake pressure, and throttle to help keep all four wheels of the car gripped firmly to the road.

Tyre Load Index

The ‘load rating’ given to a tyre by the manufacturer, which indicates how much weight the tyre can handle at a specific pressure.

Tyre Speed Rating

The maximum speed the tyre can sustain safely for a 10-minute period.


Holts Tyreweld is an emergency puncture repair product which allows you to quickly seal and reflate a tyre at the roadside. The tyre should then be inspected by a professional and either repaired or replaced.


Vacuum Lines and Hoses

Tubes that carry air, fluids and gases through the engine bay and exhaust system.

Valves Per Cylinder

The number of intake and exhaust valves found per individual cylinder of an engine.


Water Pump

The pump is used to circulate coolant/antifreeze through the cooling system, connected to the radiator and the engine by a series of hoses and coolant pathways in the engine.

Wheel Alignment

The process of adjusting components to a specified camber, toe, caster and ride height to balance the suspension and improve tyre wear.

Wheel Bearing

Wheel bearings allow wheels to turn rapidly and spin freely without generating an excessive amount of heat. A wheel bearing normally comprises of greased roller-type or ball bearings in the wheel hub, allowing for easy and frictionless rotation. 


Holts Wondarweld is a professional cooling system leak repair formula that can repair cracks and small holes in the head gasket, cylinder head and engine block.