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#PopTheHood: A Dipstick’s Guide to Engines

Some people are geniuses when it comes to mechanical things. They can rebuild transmissions, restore junkyard antiques, or recharge flux capacitors.

But most people aren’t so mechanically inclined. Perhaps your only repair experience is that you’ve aired up a low tire once or twice. Or, your knowledge of engines may be limited to the fact that your car (apparently) has one.

If so, this post is for you. We want to help people have a basic understanding of how their cars work, so that you have some idea of how to care for them or what you should do if something goes wrong. It certainly won’t turn you into a master mechanic, but it will help you talk with them, and might just save you a few dollars down the road.

For a broad overview of what’s under your hood, check here. Today, we’re going to talk specifically about the number one part of your car: the engine.

Engine Basics

There are many different types, sizes and styles of car engines, but most all of them work the same way.

Let’s start with what you can see. If you pop the hood on your car, the engine will be the centerpiece and the biggest single part. The front of the engine will have a number of spinning pulleys and parts driven by one or more rubber belts, while the back of the engine connects to the transmission.

In most front-wheel-drive vehicles, the engine is placed sideways, so that the “front” and “back” face left and right. This is called a “transverse” engine placement.


Transverse engine in a BMC Mini. Photo source.


Most rear-wheel-drive or all-wheel-drive vehicles will have the front of the engine facing the front of the car and the rear facing the rear; this is sometimes called a “longitudinal” arrangement.


Longitudinal engine in a 2004 Dodge Viper. Photo source.


Engines are commonly referred to by their shape and number of cylinders:

A V8, for instance, has eight cylinders arranged in two rows (“banks”), with the cylinders forming the shape of a “V” when viewed from the front. A V6 has the same shape, but two fewer cylinders.


1996 Mercedes V6 Rennmotor. Photo source


“Inline” engines have just one bank of cylinders all in a row; an inline engine with 4 cylinders might be called an I4 or a “straight four.”


In-line engine in a 1953 Corvette Convertible. Photo source


Less common are “flat” or “boxer” engines, which have cylinders that lay horizontally.


UL Power flat engine. Photo source

How Engines Work

Attached to the top of the engine will be either the air filter, or (more commonly) a large tube that leads to the air filter, which is usually housed in a black plastic container. Replacing the air filter, by the way, is one of the easy repairs that literally anyone can do; it doesn’t even require tools.

The air filter cleans the air that then goes into the engine cylinders and is mixed with fuel from the fuel tank. This fuel/air mixture enters each cylinder through valves. In diesel engines, the high pressure caused by the cylinder compressing the fuel/air mixture is enough to ignite the diesel; in gasoline engines, spark plugs are used to ignite the gas. You can find the spark plugs on the outside of the engine by following the electrical wires that lead to each one.


Sparkplugs on a Nissan S20 engine. Photo source.


The small explosions push the cylinders down, turning the crankshaft at the bottom of the engine. The crankshaft connects to the transmission, which uses gears to adjust the speed of the rotation. The transmission turns the drive shaft, which transfers power to the wheels and thereby moves the car down the road.

The exhaust, meanwhile, is pushed out of the engine cylinders through exhaust valves and exits through the metal pipes that extend from the side of the engine. Exhaust pipes are generally the hottest part of the car, by the way, and are the last thing you would want to touch with your bare hands.

There are many more details we could get into about the insides of engines, of course, but we’d rather show you this cool infographic with animated models of how they all work. And in reality, most people won’t ever open up and rebuild an engine; you’re much more likely to replace spark plugs or work on parts that surround the engine, such as the alternator or air conditioning system. But we’ll cover those details in later posts.