Whatever fancy tricks your car may have up its sleeve, everything eventually comes back to one thing: the engine. The engine is the heart of your vehicle, the mechanism that allows it to do what it’s meant to: move you from one place to another. It’s a brilliant technological innovation.
While it’s possible to understand the components of a car, knowing how the engine works brings the entire machine together. That understanding can also be a huge boon to you as an amateur mechanic. After all, if you know how the heart of the vehicle works, you’re much more equipped to work on it.
That’s what this article is going to focus on. There are many articles that explain how engines work, to varying degrees of success and readability. This article focuses on understanding your engine as part of a wider machine so that you can better work with it and follow its component parts in the future.
As such, this article needs to focus on one specific kind of engine: a gasoline internal combustion engine. We hope that, by the end of this article, you can look at your car with understanding instead of confusion. And that the next time you need a repair, you might be able to get in there and take care of it yourself.
Work Around the Engine
While this article explains the inner workings of the car’s engine, it’s important to note that unless you’re a professional mechanic—or a hobbyist mechanic who’s invested enough hours to be professional—it’s rare that you’ll be taking apart the engine itself. Many of the engine’s component parts are precision-made, and the very act of taking it apart could do more harm than good if you aren’t qualified. More importantly, resolving a mechanical issue might likely necessitate the removal of the engine from the car. Given that they weigh on average 350 pounds, you need specialized equipment to remove it without risking damage to yourself or the vehicle.
Instead, you’ll usually be modifying and working with the parts around the engine. Nevertheless, knowing how the engine works, and which components to look at, gives you a better understanding of this process.
How Your Engine Works
Most articles on engines are heavy on complex diagrams and lists of parts. We’re going to take a different approach here. We’re going to follow the journey of energy through your engine, starting with the fuel, tracing how that fuel becomes energy and motion, and ending where all of that energy and motion eventually goes. Parts you’ll want to remember will be in bold, while ingredients and byproducts will be in italics.
The journey starts when you press the gas pedal in your car. When you do, the fuel pump, which has begun to pressurize the fuel system the moment you turn the key to the on position, begins the process of pumping fuel into your engine. The fuel travels from your tank to the car’s engine. The fuel injector will spray a precise amount of fuel into the cylinder. At the same time, a piston in the cylinder will descend as an air intake valve opens, the combination of which sucks filtered air into the cylinder, much like drawing liquid into a syringe. Air travels through the air filter first, then through the air intake manifold, which directs it to the air intake valves. You can’t see the valves when you pop your hood —you will likely only see the air filter and possibly the top of the intake manifold, which look like a bunch of plastic tubes that connect from your engine, to a black plastic box. In any case, the cylinder is now filled with fuel and air… everything you need for a fire. The intake valve then closes, and the piston shoots back up, compressing the air and fuel mixture, creating a more efficient boom.
A distributor connected by spark plug wires to each cylinder of the engine (yes, there are more than one) sends electricity to the cylinder that just finished compressing. There, the spark plug ignites the mixture, causing the compressed mixture to burn and expand, forcing the piston back to the bottom of the cylinder. Finally, the piston comes back up, pushing the spent mixture out through exhaust valves as exhaust. These all connect to the exhaust manifold, which connects all the pipes together. The exhaust goes through there, to a catalytic converter that reduces toxic chemicals in the exhaust, and out through the muffler, which reduces noise. If you’ve ever wondered why the exhaust pipe is hot enough to burn, there’s your explanation: exhaust is freshly burnt gas.
This is what’s called a “four-stroke” process, and it repeats as long as the car is running, looping into itself ad infinitum. It’s the piston you need to pay special attention to. While it pulls gas in, compresses it, and pushes exhaust out, it’s moving up and down. On the other end of the piston is a connecting rod. This connecting rod leads to the crankshaft, which can be thought of as a giant pole near the bottom of the engine block. The pistons are oriented in an up-down position relative to your car, while the crankshaft stretches from front to back. The movement of the piston works a little like an inverted crank on a jack-in-the-box or a bicycle pedal, converting up and down motion into circular motion and spinning the crankshaft. As the piston goes up and down, the connecting rod goes in a circle, and the crankshaft carries this circular motion out of the engine and, eventually, to the wheels.
This is the key to how an engine functions: the pistons and crankshaft convert heat energy from the explosion of fuel and air into circular movement energy.
The exact timing of the intake and exhaust valves mentioned above is controlled by cams on the camshaft, which is not unlike a secondary crankshaft, oftentimes above the pistons. This is intentional: the camshaft is connected to the crankshaft by the timing belt or timing chain. As the crankshaft moves with the pistons, the camshaft opens the valves above at exactly the time needed.
Another belt, sometimes called the alternator belt or serpentine belt connects from the end of the crankshaft, in the same way as the timing belt, but to the alternator. This spins the alternator, which uses that circular energy to generate the electricity that charges your battery and runs other electrical functions on the car. This belt and others help power your air conditioning compressor, water pump, or power steering pump, each of which are self-explanatory.
Meanwhile, all of this is kept running smoothly by the oil that you put in your car’s engine. An oil pump keeps the oil, held by the oil pan at the bottom of your engine, flowing through the oil filter and to all these moving parts. This does many things, including cooling the engine, improving sealing, and lubricating parts so they don’t grind against each other.
So, let’s recap. Piston goes down, drawing air into the cylinder as it’s filled with fuel. As the piston goes back up, the valves are closed and the mixture is compressed. The distributor sends electricity to the spark plug, igniting the air and fuel, thus forcing the piston back down. This turns the crankshaft, which carries that circular energy to the wheels, and to a series of belts that power the alternator and accessories. Then, it all starts over again, thousands of times a minute.
As ingenious as all this is… it’s also fairly simple once you understand how it works: the engine draws in boom juice and air, blows it up, and uses that explosive force to spin a shaft that makes it do things.
Turning this Into Practical Knowledge
There are two ways to go about solving mechanical problems. The first is to look up the problem, itself, and hope you find the right solution. The second is diagnosis—the gradual elimination of possible causes for the problem until you hit on the correct solution. When you understand how the engine works, diagnosis becomes much easier and more satisfying. It also decreases the chance of wasting time and money on the wrong solution, and being able to anticipate how one repair may affect other parts of the vehicle.
Always trust your senses. What do you hear? What do you see? What do you smell? What do you feel? Sometimes, your car will just sound different, smell different, feel different, or look different. What, if anything, are your gauges telling you?
Looking at the outline above, it becomes possible to separate categories of car issues into six groups: moving parts, oil, fuel, air, coolant, and electricity. All parts of a car—and their functions and issues—focus on one of these five. And if any one of them stops completely, your car doesn’t run. Or, in the case of oil, it destroys itself. There are, of course, parts that interact with several categories. The spark plug can be seen as a bridge between the electric, fuel, and air categories.
Understanding how these all fit together means that, when your car is experiencing issues under the hood, you can start asking yourself which category the issue fits into and exclude the others. If you hear high-pitched squeaking, for instance, that seems unlikely to involve the fuel, air, oil, coolant, or electric systems. It must be a moving part, right? If you can hear the engine sputter when you push the gas, you can think through the process of fuel moving to circular energy, and figure out where, along this path, the problem is likely occurring. If it’s doing that when you press on the gas, it’s likely before the explosion of fuel has translated to mechanical energy, but after the fuel has reached the piston. Instead of looking helplessly over the entire engine, you know that the most likely culprit is up where fuel becomes fire. In this case, it could turn out to be the spark plug,distributor, or a fuel injector.
In other words, the key to turning all of this into practical mechanical knowledge is taking a moment to think about the problem your car is having, think about what you now know about the engine, and figure out where that problem is most likely originating.
But doing so is difficult, at best, until you understand how your engine works. Hopefully, you’ve now taken a long stride towards doing exactly that.