Different Fluids Your Car Needs and What They Do

March 22, 2021

Do you like to sip a refreshing glass of lemonade or iced tea on a hot summer day? And on those bone-chilling Iowa winter days, hot coffee, cocoa with marshmallows, or herbal tea with honey really hit the spot! Our bodies need liquids, especially water. Similarly, our vehicles need a variety of fluids to make them operate well and serve us for many years.

Here’s a quick overview of the fluids your car needs and what they do:


This gold-colored liquid powers your vehicle and is essential to proper operation. When you put gas in your vehicle, the gas goes from the gas tank to the fuel pump, which pumps the gas into the fuel lines (strategically placed away from heat and exposure to the elements). Lastly, the gas passes through the fuel filter, removing debris and impurities. Once it reaches your engine, you’re good to go, until the meter moves close to “E” for empty.


The fluid that needs to be changed the most often is the engine oil. It provides necessary lubrication for an engine’s crankcase, preventing heat and friction from destroying valves, pistons, and other parts. You don’t want to put off oil changes! Dirty oil and a clogged oil filter will cause internal wear and tear that can cause damage or even make your vehicle unusable. If you regularly have your oil changed according to the manufacturer’s recommendations, your vehicle could provide you with 200,000+ miles of service.

Brake Fluid

Probably the most important vehicle fluid for passenger safety is brake fluid. The brake-line system uses hydraulic pressure to control the vehicle’s ability to stop. When you press down on the brake pedal, the brake fluid is forced toward the pistons in the brake caliper and wheel cylinder. This increases pressure, sending the fluid into motion, causing the brake pads to compress against the rotors that are attached to the wheel, which stops the rotation. Brake fluid should be replaced by a professional every 30,000 miles.

Brake lines must also be kept in good shape because a rusty brake line can cause the brake fluid to leak out. When this happens, you could press on the brake and have it go all the way to the floor. If brake fluid failure happens while you’re moving, you could have a collision, so be sure to have your brake lines checked for integrity every so often.

Power Steering

Power steering fluid makes it possible for you to steer your vehicle with ease. If you’ve ever driven an old tractor, you may know what it’s like not to have power steering! The power steering system uses a hydraulic pump (powered by the engine), making it easier to control your vehicle. Dirty power steering fluid damages the power steering pump and other parts of the system. So, be sure to ask your mechanic to check your power steering fluid levels.

Transmission Fluid

Similar to motor oil, transmission fluid cools and lubricates the inner parts of the transmission. In some cases, it also provides the hydraulic power necessary to shift gears in an automatic transmission. A qualified service technician should flush and refill the transmission, replace the filter, tighten the transmission valve body bolts and install a new transmission oil pan gasket to avoid any leaks. Transmission fluid replacement is recommended every 50,000 – 100,000 miles, depending on the make and model of your vehicle.


Coolant, also known as antifreeze, is a heat transfer liquid. It cycles around a running engine, collecting heat as it flows through and returns it to the radiator. In most climates, coolant is a 50/50 combination of water and radiator coolant; in colder climates, the ratio will contain more coolant. Without proper coolant levels, a car will quickly overheat and be inoperable. Always be sure your vehicle has proper antifreeze levels before traveling a long distance.

Differential Fluid

This often-forgotten fluid is just as important as engine oil. The differential fluid distributes power created by the transmission to each wheel, accommodating the different speeds and distances each wheel rotates. For example, when you’re turning a corner, the inside wheels rotate less than the outside wheels. Changing the differential oil is one of the most overlooked maintenance services and should be changed every 30,000 – 50,000 miles. 

Windshield Wiper Fluids

While this is not an essential fluid in operating or stopping your vehicle, it is necessary for having a clear view for driving through rain, sleet, and snow. It is also useful in clearing your windshield of dust, bug debris, and other random particles. The fluid is easily replaced by the vehicle owner as needed. You can find specialized windshield wiper fluid for winter that will also help you de-ice your window.

Air Conditioner Refrigerant

There is nothing more refreshing on a hot summer road trip than cool air blowing through the vents! The cold air generated by your A/C system is actually hot air with hot gases removed during a multi-step process. Changes in pressure cause changes in temperature. The compressor pushes refrigerant gas through the system to provide cool air.

Your AC system probably doesn’t need to be recharged/refilled very often. If you notice the air isn’t blowing as cool as it should make an appointment. Since this process uses special equipment, you may need to go somewhere other than your trusted mechanic: ask him to recommend someone to you.

Battery Fluids

Vehicles with maintenance-free batteries don’t require checking of the battery fluid. Other car batteries, however, must have their individual cells refilled from time to time. Your mechanic can check your battery during regular vehicle maintenance.

We hope this brief overview of car fluids has helped you understand better how your car works and what you need to do to keep it in good running condition. In order to ensure safety for you and your family, as well as prevent costly repairs or replacements, regular maintenance is the key! And, if you happen to have a brake failure or other mishap that causes a collision, just let us know. Waln Repair & Collision Center is here to help you get back on the road as soon as possible!