Car Fluids 101: Protecting Your Vehicle’s Liquid Assets

Here are the most important car fluids and why they matter.


Just as your body needs water, your vehicle needs certain fluids to run properly. When they run low or become contaminated, your car becomes less efficient and can break down.

Find out why these seven car fluids are critical to keeping your car running smoothly.


What it does: Oil lubricates, cools and cleans moving parts in the engine.

Why it’s important: Without proper lubrication, engine parts stop moving, possibly damaging the engine beyond repair.

Top consideration: Synthetic oil is more expensive than traditional motor oil, but it performs an average of 47% better than conventional oil. Among the advantages of synthetic oil are better low- and high-temperature viscosity performance, increased stability, and less initial drag on the engine for improved horsepower and torque.


What it does: Transmission fluid lubricates moving parts within the transmission and helps maintain the hydraulic pressure necessary for changing gears. It also keeps seals flexible and acts as a coolant.

Why it’s important: Transmission gears eventually wear and fail without adequate lubrication.

Top consideration: Your transmission fluid doesn’t need to be changed often—depending on your vehicle’s typical driving conditions, transmission fluid can last 100,000 miles or more. But it’s certainly less expensive to replace the fluid than your entire transmission, so get the level checked.


What it does: Brake fluid transfers the proper hydraulic force to brake pads or shoes, which create the friction that stops your car when you apply the brakes.

Why it’s important: If the fluid is low or too much air gets into the brake line, you may not be able to properly stop your vehicle.

Top consideration: If the brake fluid level is low, there is likely either a leak or some other serious problem in the brake system. Have a qualified technician inspect the brakes right away.


What it does: This fluid powers the steering gear and makes steering easy. It also helps protect seals and rubber hoses in the system.

Why it’s important: Low levels of fluid cause the steering wheel to stick or catch, making it difficult to turn the wheel (and your car).

Top consideration: A buzzing noise when the steering wheel is turned at low speeds can indicate that the power steering fluid is low.



What it does: Coolant keeps the engine from freezing up in frigid temperatures, helps prevent overheating in summer, lubricates the water pump seals, and protects the cooling system from rust and corrosion.

Why it’s important: Without the proper coolant level, a car’s engine will quickly overheat.

Top consideration: At least once a year, preferably before the onset of winter in colder regions, get your coolant tested to determine its level of antifreeze protection.


What it does: This fluid clears dirt and grime from your windshield.

Why it’s important: A dirty windshield compromises your ability to see the road clearly.

Top consideration: In colder areas, make sure you are using a fluid formulation that won’t freeze on your windshield.


What it does: Fuel is a vital part of the combustion process that powers vehicle

Why it’s important: Check your vehicle owner’s manual to determine which type of gasoline or diesel fuel is recommended or required. Using the proper grade of fuel can have a significant impact on your vehicle’s performance and reliability.

Top consideration: AAA Members save at least 5¢ per gallon at participating Shell stations when joining the Fuel Rewards® program. Restrictions apply.

Car fluids: General DIY tips

  • Consult the maintenance schedule in your vehicle owners manual to determine when specific fluids should be replaced.
  • Only use car fluids that meet the automaker’s specifications.
  • Park on level ground when you check fluid levels.
  • Don’t overfill–too much fluid could be as harmful as too little.
  • Before removing dipsticks and reservoir caps, clean around them to help keep out contaminants.
  • If you find that your car’s fluids need to be topped off frequently, get it checked out by a mechanic.

When you go the DIY route, remember that AAA Members save 10% and earn NAPA Rewards points on most auto parts and accessories at NAPA.

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