How to Check the 5 Essential Fluids in Your Car

Here is a quick rundown of the five most important fluids found in most cars, and how to check the levels, from guest blogger Toby Schultz, Master Mechanic at YourMechanic.

QDT Editor
4-minute read

One of the easiest and most important things you can do for the wellbeing of your vehicle is to ensure that the fluids are kept at the proper level and in good condition. Performing regular scheduled maintenance addresses the condition of the fluids, but it’s also important that the fluids remain at the correct level between these services.

Here is a quick rundown of the 5 most important fluids found in most cars, and how to check the levels. 

1.) Engine Oil

Description: All internal combustion engines require engine oil to lubricate the many moving internal parts. Engine oil is the lifeblood of your car.

Precautions: Used motor oil is a potential carcinogen, so please be sure to wear gloves if you have them, and wash your hands thoroughly after handling motor oil.

Risks: Letting the oil get below the minimum level of the operating range can have detrimental effects on engine performance, including the possibility of complete engine failure.

How to check: Most vehicles have an oil dipstick, with maximum and minimum marks, for checking the oil level. Pull the dipstick all the way out and wipe the bottom clean with a dry rag. Then re-insert the dipstick completely, and remove it again, this time keeping it held upright or flat so the oil doesn’t run up the dipstick causing an inaccurate reading. Where the dipstick is now covered in oil is where the level is; ideally somewhere between the maximum and minimum marks.

2.) Engine Coolant

Description: Despite the name, there is nothing cool about engine coolant. Heat is a normal byproduct of the internal combustion engine. The cooling system absorbs this heat and dissipates it through the radiator, allowing the engine to remain at a designated operating temperature.

Precautions: The engine coolant can be quite hot and under a lot of pressure. This can make opening the system very dangerous. If you do have to open the system, please be careful to only do so on a cold engine, and do it very slowly, or you risk getting seriously burned.

Risks: A low coolant level can lead to overheating of the engine, which can cause severe damage to it.

How to check: The best way to check your coolant is after the car has been sitting for several hours, usually first thing in the morning after sitting overnight. Some vehicles allow you to check the level simply by looking through a translucent coolant expansion or overflow tank, and verifying that the level is between the minimum and maximum marks. Others require that you open the radiator or pressurized expansion tank (commonly found in BMWs) to check the level. 

3.) Brake Fluid

Description: When you depress your brake pedal, the master cylinder (which is attached to the brake pedal) moves brake fluid through the brake lines and into the brake calipers or wheel cylinders where it is used to apply the brakes.

Precautions: Brake fluid is hygroscopic, which means it absorbs moisture in the surrounding environment. Keep all brake fluid containers and reservoirs tightly sealed until you need to add fluid, then immediately seal them up again after adding the fluid. Brake fluid is also extremely damaging to paint, so if you spill any, be sure to thoroughly wash the area with soap and water right away.

Risks: If the brake fluid is allowed to get too low, you could experience a loss of brake pressure, or even a complete brake failure.

How to check: Most modern vehicles use a translucent plastic reservoir that allows the fluid level to be checked without opening the system. As with the other fluids, you are simply looking through the reservoir to see that the fluid level is between the minimum and maximum marks.

4.) Power Steering Fluid

Description: Many manufacturers now equip vehicles with much more efficient electric power steering systems. Despite this fact, there are still plenty of vehicles using older-style hydraulic power steering systems. These systems use pressurized power steering fluid to assist you in turning the steering wheel.

Precautions: Power steering fluid varies between manufacturers, and some are potential carcinogens. Just to be safe, I suggest you wear gloves and thoroughly wash your hands after handling the fluid.

Risks: Low fluid levels can cause a loss of steering assist or a total failure of the power steering system, which could result in an accident.

How to check: Most power steering reservoir caps have a small dipstick built into them, or they use a translucent reservoir that allows you to view the fluid level from the outside. The process is similar to checking engine oil: Remove the dipstick, wipe it clean, and then re-insert and remove it again. The level should be between the minimum and maximum marks. If it's the type with the translucent reservoir, just look through it to see that the fluid level is between the marks.

5.) Windshield Washer Fluid

Description: Windshield washer fluid does exactly what the name implies—it washes the windshield of your car.

Precautions: Washer fluid is pretty innocuous, though depending on the alcohol and detergent content, it is a potential skin irritant. If you get some on your skin, you can simply wash it off with soap and water.

Risks: The only risk you run by having low washer fluid is that you may run out of fluid and be unable to clean your windshield when you need to, potentially limiting your visibility while driving.

How to check: The nice thing here is that you don’t actually need to check the level. Most vehicles don’t even have a way to check the level. Instead, if you run out or you believe the fluid is getting low, you can just fill the reservoir all the way back up to the top any time you want—there’s no risk of overfilling it.

Disclaimer: This list is neither all-inclusive nor vehicle-specific. It is meant to serve as a general guide to the most important fluids in the majority of cars on the road. If you’re having trouble locating any of the fluids listed above, the vehicle owner’s manual usually has a diagram specific to your car model.

These checks should be performed when the vehicle is stationary, on a level surface, and with the engine off. If any of the fluids are found to be low, it is strongly suggested that you top them off with the correct fluid (e.g., the correct weight of oil, not just any oil you have lying around) and have the vehicle inspected by a certified mechanic to diagnose why the fluid level was low.


Toby Schultz is a Master Mechanic at YourMechanic, which delivers mobile car repair by certified mechanics in over 300 U.S. cities. Their top-rated technicians can perform over 400 services at your home or office and will even answer your questions online.