Under the Hood: Everything You Need to Know

By Jed Lehman •  Updated: 11/22/21 •  16 min read

When you pop open the hood of your gasoline car a lot is going on. While everyone knows cars have engines under the hood, there’s more than just an engine under the hood. Vehicles also have other components that work together with the engine to transmit power to the wheels or to make your driving experience more pleasant. Moreover, there are several fluids and electrical systems that you should be aware of when working on your vehicle. 

If you’re not sure what you’re looking at when you pop the hood of your car you’re in the right place. We’re going to take you through everything you need to know about the components under the hood of your vehicle. That said, this is a general guide for gasoline engines, although it does share similarities to electric and diesel motors.

Read on to learn more.


A combustion engine is made up of many moving parts. There’s the block, the pistons, camshafts, and more. While you can’t see every part of the engine by opening the hood, you can see most of them. We’re going to take you through a handful of common engine components and provide a brief description of their functions.

Engine Block 

Engine blocks are the glue that holds your engine together. It’s the shell of your engine and is typically made from durable metals like iron. The engine block houses the pistons, crankshaft, camshaft, and the engine’s cylinders. It also holds the pistons within the cylinders and can be constructed in a V shape or a straight line (known as in-line).

Cylinder Head 

The cylinder head is where the combustion part of an internal combustion engine happens. The cylinder head houses the pistons, various valves, pushrods, rockers, and even camshafts. The cylinder head controls the flow of air into the engine’s cylinders during the intake stroke and exhaust stroke.


Pistons are cylindrical apparatuses that have a flat surface on top with various rings attached. The piston transfers energy from combustion to the crankshaft, which is what propels the vehicle. Pistons travel up and down within the cylinder two times every time the crankshaft rotates. The rings attached to pistons are used to reduce the friction and damage from constant rubbing along with the cylinder. Piston rings also help with compression.

Connecting Rod

Connecting rods are attached to the bottom of pistons. The connecting rod is used to connect the pistons to the crankshaft. The connecting rod also makes it easier for the pistons to pivot and rock.


The crankshaft is in the lower area of the engine. It’s the mechanism responsible for moving the pistons up and down within the cylinders and it’s connected to all of the pistons in a vehicle. While the location of the crankshaft varies, every vehicle that uses pistons needs to have one to transfer the force created by combustion within the cylinders.


The camshaft can be in two places depending on the vehicle. It’s either in the engine block or within the cylinder heads. That said, most vehicles have them located within the cylinder head, which is known as an overhead cam (these can be single or dual). The camshaft is responsible for valve timing, moving the pushrods, and controlling the movement of lifters.

Rocker Arm

The rocker arm is a small component that manages the movement of the camshaft. It moves the camshaft towards the intake or exhaust valves within an internal combustion engine. The process occurs through direct contact.

Timing Belt 

The timing belt is a strong rubber belt with gears to grip pulleys from the crankshaft/camshaft –it almost resembles a bike chain. It’s designed to synchronize the movement between the camshaft and crankshaft, which ensures valves open and close when they’re supposed to. The timing belt also prevents the pistons from hitting the valves, which could cause expensive damage.

Spark Plugs 

Spark Plugs are responsible for starting your vehicle. Without the spark plug, there’s no electrical jolt that turns over the engine. Spark plugs are small components that have a central electrode (protected by a threaded metal shell) and they’re connected by an insulated wire. The connection connects the spark plug to the output terminal of the magneto or ignition coil. Spark plugs are a wear item and can break down over time, which requires replacement.


The flywheel is what makes modern vehicles smooth to drive. Without a flywheel, cars would be jolty, which is uncomfortable and bad for engine components. The flywheel works by storing rotational energy produced by the engine. It stores energy by using the conservation of angular momentum produced by the engine. Flywheels are necessary because engines deliver inconsistent levels of torque.

Exhaust Manifold 

The exhaust manifold is responsible for catching exhaust gases caused by combustion. Once it has the gases from each cylinder the exhaust manifold sends the air to the exhaust pipe, which is responsible for sending the exhaust fumes away from the cabin and engine.

Intake Manifold 

An engine’s intake manifold holds things like the throttle valve and some other engine components. The purpose of the intake manifold is to send air into the cylinder head and cylinders. Air enters the intake manifold through an air intake, which sucks up outside air.


Gaskets are found all over the engine and its various components. Gaskets are used to seal parts of the engine to prevent leaking. There are gaskets for the cylinder heads, intake manifold, exhaust manifold, and other parts of the engine.

Innovation continues to improve engines, so some vehicles might have different components under the hood.

Cooling System  

engine coolant

Every vehicle has a cooling system to prevent components from overheating. While engines are warm, an engine that’s too hot will begin to wear down and break. Overheating can lead to ruined oil, blown head gaskets, and total engine failure. Therefore, knowing what components make up the cooling system is important.


The radiator of a car is typically made out of aluminum and consists of numerous pipes with small fins attached. Radiators act as heat exchanges and swap the hot air from the engine with the ambient air from the engine bay. This is done through a combination of methods with one of them being engine coolant.

Water Pump 

The water pump is responsible for sending coolant around the engine. It acts as a bridge between the radiator and the rest of the engine. It’s a small component with metal blades on the bottom that spins in a circular motion. The water pump sends coolant to the cylinder heads, heater core, and cylinder block. Once the coolant completes its cycle the water pump sends the coolant back through the radiator.


The thermostat is a valve with the sole purpose of letting coolant pass through the radiator. When the engine reaches a certain temperature the thermostat opens and allows coolant to flow freely through the radiator. The thermostat opens and closes with the help of paraffin wax, which expands once the engine reaches certain temperatures.


Not all cars have fans for cooling and vehicles that have fans have them in different locations. Moreover, vehicles can have one or more fans depending on the demands of the cooling system. That said, a fan is a simple component. It turns on when the engine reaches a certain temperature aids in the cooling process.

Battery and Electrical Systems 

car battery

Under the Hood of every vehicle, gas-powered or electric, you’ll find electrical components. Most vehicles will have a battery and fuse box, so knowing what they are and how they work is helpful.


Automotive batteries are big, rechargeable batteries used to start vehicles and operate electrical systems when the engine is turned off. Car batteries work by converting chemical energy in the battery cells into electrical energy. Then it delivers an electrical current to the starter, which starts the vehicle. Car batteries also maintain an engine’s ideal level of voltage to keep the engine running. These batteries are charged by the alternator when the vehicle is running.

The battery is the central electrical hub for most vehicles. Without the battery, cars can’t start and you won’t have any power if the engine is turned off. While they’re rechargeable, car batteries do wear down over time and need to be replaced every 3 to 5 years.

Fuse Box 

The fuse box is responsible for delivering energy to different systems of a vehicle. Every car is different but every vehicle has a fuse box with a handful of fuses. The fuse box protects the fuses from being exposed to the elements like rain, snow, and dirt. The fuse box is essential because it makes sure the perfect amount of power is distributed. When fuses break, the electrical components of your vehicle can stop working.

If you’re interested in learning about the types of fuses and how they work for your vehicle, we recommend taking a look at your vehicle’s owner’s manual. The owner’s manual has an outline of where fuses should go and their functions.

Electrical Control Unit (ECU)

The electrical control unit (ECU) is a small electrical control unit that controls actuators for the engine. The ECU is one of the most important parts of a vehicle’s electrical system because it processes information and ensures the engine is operating smoothly. When there is an issue with your vehicle, like the check engine light coming on, the code comes from the ECU.

Mass Airflow Sensor (MAF)

The mass airflow sensor is a critical component of modern vehicles. The sensor is responsible for controlling how much fuel mass is delivered to the cylinder heads based on the temperature and density of inlet air. These devices are found on all fuel-injected combustion engines.

Other Sensors

Internal combustion engines also have other sensors that provide data for a vehicle’s ECU. While some cars have more or fewer sensors than others, we’ll provide you with the basic sensors found in most modern vehicles:

All of these electrical components and sensors work together to ensure the engine is running properly at the right voltage and that each system is performing optimally.


car transmission

The transmission is the second-largest component you’ll find under the hood. Attached to the back of most engines, the transmission is responsible for transferring power to the drivetrain.

Automatic Transmissions 

Automatic transmissions are the most common transmissions in modern cars. There are many variations and configurations but they all perform the same purpose. Automatic transmissions use hydraulic power to shift the gears inside of the gearbox. In most vehicles, this process occurs by combining a torque or fluid coupling with gear sets. With automatic transmissions, vehicles can idle without stalling and remain in gear. The torque converter connects to the engine and transmission and delivers pressurized fluids to transfer power.

Manual Transmissions 

Manual transmissions used to be more popular but demand has shifted in favor of the automatic transmission. Manual transmissions use a combination of components to shift gears and deliver power to the wheels. Manual transmissions use a clutch to separate the transmission from the engine. When the clutch is engaged the engine can idle without stalling. Manual Transmissions are known as manual transmissions because the driver has to use the gear shift to select which gear to drive in.

Manual transmissions use forks that are connected to the gear shift and transmission to switch gears. There is also a clutch pedal that needs to be pressed before switching gears. In most manual transmission vehicles there is gear oil that keeps the gearbox lubricated instead of transmission fluid that’s found in automatic transmissions.

Regardless of the transmission your vehicle has, every vehicle needs one to transfer power from the engine to the drivetrain. 

washer fluid


Under the Hood of your vehicle, there are different types of fluids. These fluids help your vehicle run properly, prevent engine overheating, and allow you to use things like power steering. We’re going to give you a breakdown of these essential fluids.

Checking the Oil 

Oil is responsible for cleaning, lubricating, cooling, sealing, and actuation. Engine oil is the lifeblood of the engine and makes sure the parts don’t wear down quickly. Without oil, many parts will begin to fail because of the friction created within engines based on the moving parts. 

You can check the oil level and how the oil is holding up via the oil dipstick. While the location changed based on the make and model of the vehicle, dipsticks typically have a yellow handle that you can remove with your fingers.

Windshield Washer Fluid 

Windshield washer fluid is a liquid that’s designed to clean your windshield. There are many different types but some of the common uses for washer fluid include cleaning up bug guts, preventing frost from accumulating on the windshield, and de-icing windshields. Based on where you live and your needs, you should choose a washer fluid that’s right for you.

Transmission Fluid 

Transmission fluid is found in vehicles with automatic transmissions. Similar to how oil keeps the engine clean and lubricated, automatic transmission fluid performs a similar job. It helps the transmission handle and transfer the power from the engine and keeps the gears clean and lubricated. While automatic transmissions have this red or green fluid, vehicles with manual transmission do not.

Power Steering Fluid

Power steering fluid is a hydraulic fluid that’s used in the steering system of most vehicles. In the past, turning the wheel was challenging because there wasn’t much lubrication or additional leverage. Today, power steering fluid solves this problem by keeping the power steering pump clean, lubricated, and corrosion-free.

Brake Fluid

Brake fluid is a hydraulic fluid that’s designed to make braking easier and more efficient. Braking fluid transfers force into pressure, which amplifies total braking force. Without brake fluid braking would be much harder and your brakes wouldn’t last nearly as long.


Coolant is responsible for keeping your engine cool and it also protects against engine components freezing in the winter. While there are differences between coolant and antifreeze, most modern vehicles rely on antifreeze because the mixture can handle high and low temperatures. Plus, it’s typically affordable. Most engine coolants are made with a combination of ethylene glycol or propylene glycol. These chemicals are mixed with water to produce engine coolant.

Depending on your vehicle there may or may not be more fluids under the hood. In most cases, these are the common fluids you’ll find under the hood.

Air Conditioning (AC)

Most modern vehicles have an air conditioning (AC) system to keep the cabin cool in hot conditions. While every vehicle’s AC is specific to that vehicle, every air conditioner has the same components. Understanding what they are and how they work is essential when diagnosing problems with the AC system.


The air conditioning unit in every automobile begins and ends with refrigerant. The refrigerant also has other names like freon and can change from a liquid to a gas, which is important for the cooling process. The refrigerant passes through the air conditioning system as a gas and a liquid depending on where it is in the system.


The AC compressor is located by the front of the engine in most vehicles. It’s attached to a serpentine belt, which drives the compression. The AC compressor is responsible for taking in low-pressure gases and turning them into high-pressure gases which are hotter. Once the higher temperature gas reaches the proper temperature it’s moved to the condenser.


The AC condenser is where the majority of the cooling happens. In the condenser, the refrigerant is cooled by a group of coils that remove heat from the outside gases. Once the gas is cooled it becomes a liquid. 


The accumulator is responsible for removing humidity from the cool air that enters your cabin. It features a desiccant to absorb moisture where freon passes through the rest of the air conditioning system and into your cabin. Without the accumulator, the air conditioning could be thick and moist instead of dry.


Every AC unit has a filter. The filter is a simple part of the system that’s designed to keep the unit clear. It removes debris, dirt, and other hazardous materials from the air conditioning system. These filters don’t last forever and need to be replaced after a certain amount of time to prevent premature wear within the AC system.

Expansion Valve 

The expansion valve restricts the flow of refrigerant and converts it from a liquid into a gas as it gets ready to pass through the rest of the system into the evaporator. The expansion valve is also needed to change the pressure of the refrigerant into a low-pressure mist.


The evaporator is the component of the air conditioning that sends the cold air into your vehicle’s cabin. The evaporator uses a blower motor to push cooled mist over the evaporator’s cold tubing. From there, the cooled air is pushed into the cabin.

When all of these components work together in unison you get to enjoy a fresh breeze in the cabin despite the hot temperatures in the engine bay.

Wrapping Up 

Knowing what’s under the hood of your vehicle can make a huge difference when it’s time for maintenance or repairs. Understanding the engine and the components that support it can save you time and money by helping you avoid a trip to the mechanic. While there is a lot to learn about each component, identifying what you’re looking at is a great start.

Jed Lehman

Jed Lehman is a born gearhead who has been working on cars since he could crawl. He inherited his love for auto from his grandfather who owned a maintenance shop in Carlsbad, California. Jed is the driver behind Gearshift, and started this site to provide straightforward, helpful automobile information. From maintenance tips to product reviews, you can find it all here.