What fluids are in a car and what do they do?

Quick insights

Cars can be, in many ways, like people. We sometimes give our cars names, and they have vital parts that need regular maintenance and repairs. Another similarity is that just as people have fluids to help regulate their bodies, cars also have essential fluids that are vital to helping them operate. As a car owner, learning about these fluids may be helpful, since most car maintenance routines recommend checking them periodically. Let’s explore some of the major fluids that keep your vehicle running.

Regular or diesel fuel

A prominent fluid for any vehicle is its gasoline or diesel fuel. This fluid is essential for powering an internal combustion engine. Fuel is stored in the gas tank and moves through fuel lines, typically aided by a fuel pump, before being injected into the engine cylinders where it ignites to create power. Understanding the different types of gas for cars might help you choose the right option for your specific vehicle.

Engine oil

Engines have moving parts that can potentially rotate several thousand times a minute. Engine oil is an essential car fluid used to provide lubrication to prevent these parts from generating excessive friction that would wear them out faster. It also assists in cooling the engine. Because of the intense work an engine does, oil moves continuously through the engine to lubricate parts and becomes dirty over time, meaning it typically needs to be changed regularly.

You can usually find the engine oil dipstick within or close to the engine bay. When checking your oil, a mechanic might ask you to wait at least 10 minutes after shutting off the car so the engine can cool and the oil can settle. They may then remove the dipstick, wipe it clean, re-insert it and pull it back out to check the level. It’s generally preferable to keep your oil closer to the maximum level indicated. You can learn more about how to check your oil to stay prepared.

In general, engine oil is meant to be replaced roughly every few months to a year, depending on the motor, the type of oil you use and your regular driving conditions. If the oil is discolored, has a gritty feel or looks different from its usual honey or amber color, it might be time to replace it. Additionally, if you notice a honey- or amber-colored stain where your car was recently parked, or if you get a consistently low reading on the dipstick, it may indicate an engine oil leak.

Coolant (antifreeze)

Engines produce heat, and coolant is the fluid that works to absorb that heat and carry it away from the engine block, typically dissipating it via the radiator. This function regulates engine temperature and prevents damage from overheating. Coolant is also called antifreeze because it contains additives that prevent freezing in the winter, which helps prevent cold-weather damage to the engine, radiator and water pump. Coolant is generally meant to last for several years and thousands of miles at a stretch, but consult your owner’s manual for specific flushing recommendations.

Coolant is typically stored in the radiator, and there’s generally an overflow or expansion tank that gives the fluid additional space to expand as it absorbs heat. When checking your coolant, a mechanic will likely wait for the automobile to cool before looking to see that the fluid is between the minimum and maximum levels indicated on the tank. Consistently low levels of coolant could indicate a leak, as could stains matching the color of the coolant you use. If your engine oil looks cloudy, it may also indicate your coolant is leaking into it.

Power steering fluid

If you’ve ever driven a classic car, you may have noticed how heavy the steering can feel. Newer vehicles use pressurized power steering fluid to make maneuvering easier and improve responsiveness on the road. Unlike engine oil, power steering fluid is designed to last a while, and you typically don’t need to change or flush it regularly unless recommended by your manufacturer.

Power steering fluid typically has its own dipstick or cap in the engine bay. Checking it is very similar to checking engine oil, requiring a visual inspection of the dipstick or reservoir markings. A common sign of a power steering fluid leak is if you find yourself constantly having to top it off, or if the steering starts to feel sluggish and heavy. Power steering fluid is often pinkish in color, so stains or residue in this hue may also indicate a potential leak.

Transmission fluid

Transmission fluid serves a similar function as engine oil by cooling and lubricating parts throughout the drivetrain. It plays an important role in helping the transmission convert the engine’s torque into propulsion to provide smooth, seamless shifting. Some cars have “lifetime” transmission fluid that requires minimal maintenance, but you can consult your owner’s manual for specific service intervals.

If your car has a transmission fluid dipstick, checking it is similar to checking other fluids. If it doesn’t, you may have a sealed transmission that requires a mechanic to perform a more involved procedure. Transmission fluid is often a reddish-amber color. Reddish-brown stains on the ground near where you parked, consistently low fluid levels or moisture around the transmission could indicate a leak.

Brake fluid

Brake fluid helps to transfer the force from the brake pedal to the actual brake calipers. These calipers, along with the brake pads, then clamp down on the wheel to create the friction required to slow down or stop your car. Brake fluid tends to get flushed every couple of years or so, but it’s best to change it based on the manufacturer’s recommendations.

Brake fluid is typically stored in a marked reservoir in the engine bay. Checking it involves a procedure that requires taking off the cap and visually inspecting to make sure the fluid inside is near the top. Brake fluid generally has a transparent amber coloration, and any discoloration could indicate an issue. Brake fluid leaks can cause the brakes to feel irregular, spongy or soft. Visible fluids under the car or the presence of a brake warning light on your dashboard may also be potential signs of a leak.

Windshield wiper fluid

Windshield wiper fluid doesn’t make a tangible difference to the mechanical performance of your car, but it affects visibility through your windshield. Flushing out the windshield wiper system isn’t typically a routine procedure. However, if you notice uneven, inconsistent spraying—or no spraying at all—even when you have adequate fluid, it could mean there’s a blockage that requires a mechanic’s attention.

The fluid is often stored in a translucent, labeled tank under the hood, making it easily identifiable since most washer fluids come in bright colors. A visual inspection of the tank should typically suffice to check the level. Consistently low fluid levels are often the most obvious indicator of a leak, along with puddles or wet stains near the front of the vehicle.

Air conditioner refrigerant

Air conditioner refrigerant is a specially formulated fluid that absorbs heat from the cabin and releases it outside, keeping the interior of your car cool and comfortable. Unlike engine oil or windshield wiper fluid, changing or recharging your AC refrigerant is not a frequent maintenance task. However, if you notice your air conditioning is no longer blowing cold air, it may be necessary to have a mechanic check the system and recharge the fluid to keep it working as intended.

In summary

Car fluids serve a specific and important purpose in keeping your vehicle running smoothly. From the fuel that powers the engine to the oil that lubricates moving parts to the refrigerant that cools the cabin, these fluids are essential to your car's overall health. As a car owner, understanding how and when to check these fluids, as well as how to diagnose potential leaks, could help extend the quality and life of your ride.