The Essentials
Engine Compartment Basic Components

Engine Compartment Basics - Driving Test Essentials

Updated Dec. 29, 2020

Now it’s time to pop the hood and familiarize yourself with some basic features of your car’s engine compartment. It’s important to know roughly what everything is, even if you never intend to work on the car yourself. Eventually, you will need to perform basic maintenance tasks like checking oil levels or topping up coolant. The information in this guide will help you find your way around when the time comes.

Motor oil cap

You will need to find the motor oil cap whenever you want to check or top up the engine oil. The oil tank cap is usually on top of the engine, though in some vehicles it can be found high up on the side. Your vehicle owner’s manual will be able to pinpoint the exact location of the cap if you cannot find it at first glance. If you take the cap off to check, top-up or change the oil, remember to replace it when you’re done. Driving with your oil cap off can damage the engine if oil leaks from the tank and levels become too low.

Oil dipstick

When you need to check your engine oil level, you will do so with the oil dipstick. This must be pulled out, wiped clean and re-inserted into the engine. When you pull the dipstick out for a second time, the oil tide mark on the stick will tell you how much oil is in the tank and whether it needs topping up. Before checking your oil level or removing the motor oil cap, ensure the car is parked on a flat surface and the engine has been switched off for long enough to be cool.

The oil dipstick can be tricky to locate, so you may want to refer to your vehicle owner’s manual. In most front-wheel-drive engines, the dipstick is in the middle of the engine. In rear-wheel-drive vehicles, it is more likely to be somewhere near the front-left of the engine.

Radiator cap

The vehicle’s radiator system pumps coolant around the engine in a network of tubes. The liquid coolant absorbs excess heat from the engine to keep it at a safe temperature. This heat is then expelled from the vehicle via the radiator, as the heated coolant passes through it. The radiator itself is usually situated at the front of the engine, where it can release heated air through the air vents. On the top or top/side of the radiator is the radiator cap, which also serves as a pressure valve. When the coolant pressure gets too high, the valve will release hot air. Never remove the radiator cap when the engine is running, as you may be sprayed with hot coolant.

Coolant reservoir

Around the radiator, you should see one or more hoses connecting it to a separate tank. This tank is your engine coolant reservoir; in most vehicles, the reservoir is translucent and pale in color. Along the side of the coolant reservoir, there will be a line or marking indicating the minimum level that the coolant must reach when the engine is cool. If the fluid level is below this line, you will need to remove the cap and top up the coolant.

Even though locating and topping up the coolant reservoir is a straight-forward task in most vehicles, you must check your vehicle owner’s manual before removing any caps or adding any fluid. This will make sure you are in the right place, reading the level correctly and using the right type of coolant for your engine.


Every electronic system in your vehicle – including the ignition – is powered by the car battery. It uses up a great deal of energy starting the vehicle but is automatically recharged as the engine is running. In most vehicles, the battery is found in the front of the engine bay, off-set from the engine to the left or right. In some cars, the battery is fitted in the trunk compartment, though this is quite uncommon. The battery itself looks like a small, rectangular box with wires protruding from the top – it should be easy to spot. On top of the battery, there will be a positive terminal (marked with a plus symbol) and a negative terminal (marked with a minus symbol). This is where the jumper cables would be attached if you needed to jump-start your car.

Air filter

All combustion engines require a constant supply of clean air to produce energy and run smoothly. The air filter is a vital engine component, as it cleans dirt, dust, bugs and residue from the air before it passes through the engine cylinders. In most modern vehicles, the air filter can be found inside a rectangular cold air box toward the front of the engine compartment. The air filter will need to be replaced roughly every 6,000 to 12,000 miles (depending on how regularly you drive on unpaved, dirt roads). If you choose to do this yourself, you will need to unscrew the top of the rectangular cold air box to access the filter. Be sure to consult your vehicle owner’s manual before attempting to change the filter.

Windshield wiper fluid reservoir

Windshield wiper fluid helps your windshield wipers to clean dirt, grime and other residues from the windshield. It is comprised mainly of water, with a few other chemicals mixed in to prevent a “streaky” finish. It is important to top up your wiper fluid regularly so that you do not get caught with an empty tank and a dirty windshield.

The windshield wiper reservoir should always be at least half full. The reservoir itself is usually a clear or translucent tank, located at the back of the engine compartment under the windshield. In many vehicles, it will be marked with a sticker or raised print which identifies it as the wiper fluid container. On top of the reservoir, you should see a cap, which will need to be unscrewed and replaced whenever you top up the wiper fluid.

Engine compartment warnings

To stop vehicle owners from accidentally injuring themselves or damaging the engine, most car manufacturers include stickers with additional information and warning messages at key points around the engine. You are likely to find these warning labels at the front of the engine compartment, on the battery and on the radiator. While you’ve got the hood open, have a look at these labels and take note of the information they contain.

If in doubt, call a professional

If anything goes wrong with your engine, do not be tempted to explore components under the hood that you do not understand. Most motorists are capable of changing oil, wiper fluid and coolant when necessary. Anything beyond this should be dealt with by a certified mechanic unless you happen to be an experienced mechanic yourself. Keep in mind that in certain new cars, you can void the manufacturer’s warranty by messing around with the engine!

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