What Fluids in a Car Need to be Changed?

Cars need a lot of fluids. Sure there's stuff like gas or diesel that the engine converts to energy, but that doesn't begin to scratch the surface. And we’re not even talking about the age-old joke of “Blinker fluid”. Braking, steering, engine cooling systems, the transmission, and more require fluids to work properly. Learn about the different fluids you need to change to keep your ride running smoothly. We'll include an estimate for when each fluid needs to be changed, but the actual amount of time depends on what you drive, so check your owner's manual for the most accurate information.

Car Fluids You Need to Change

1. Motor Oil

When your engine is in operation, a lot of metal parts rub against each other. This rubbing would generate a lot of friction and heat without oil to lubricate the engine’s internals. Engine oil also acts as a coolant to keep hot engine parts, like the bottom of the piston and skirts cool.

Traditional wisdom puts the oil change interval every 3 months or 3,000 miles, but this interval will differ depending on your year, make, model, and engine, as well as the type of oil you use (conventional or synthetic). Check your owner’s manual for the correct interval.

2. Transmission Fluid

Regardless of whether you have a manual or Automatic transmission, it contains fluid that needs to be changed in intervals. This fluid lubricates the gears and synchros in a manual transmission, and does the same with clutch packs and gears in an automatic transmission. You don’t need to change transmission fluid nearly as often as oil, but it’s important to note that neglecting it can quickly lead to transmission failure, which is nearly as costly a repair as changing an engine. Most manufacturers recommend transmission fluid changes between 25-40,000 miles.

3. Brake Fluid

Most braking systems use hydraulic fluid with a Master Cylinder to compress Brake Calipers, which then squeeze the pads to the rotors and bring the vehicle to the stop. Brake fluid is hygroscopic, which means it absorbs water, which leads to rust, corrosion, and a lower boiling point for brake fluid, which operates at extremely hot temperatures near the caliper. Brake fluid should generally should be flushed every 25,000 miles or when the pads and rotors are replaced. Learn more about flushing brake fluid here.

4. Engine Coolant

Engine coolant, or antifreeze, does what it sounds like it would do: it cools your engine. Without it, the engine would overheat and seize. When you need new coolant and what coolant you need depends on what you drive, so check that owner’s manual, or read here about what antifreeze you need, or how to flush and fill it.

5. Power Steering Fluid

Hydraulic power steering systems use hydraulic fluid similarly to how brake fluid works. Over time, this fluid goes through a multitude of heat cycles, gets dirty, and begins to break down. Power steering fluid generally gets neglected the most out of any fluid, but it also tends to last the longest. A service interval of 60-80,000 miles is generally ok.

6. Differential Fluid

No matter what kind of car you have, you have some form of a differential, which through a series of gears, transmits the engine-to-transmission torque to the axles and wheels. 4 wheel drive vehicles generally have a front and rear differential, and many AWD vehicles have a center differential as well as a rear. This gear oil breaks down over time, gets dirty, and needs to be changed. Most manufacturers put the interval at 80-120,000 miles, so check accordingly.

7. Windshield Washer Fluid

Washer fluid isn’t a crucial maintenance fluid in that your car can still function without it. That said, you’ll regret not topping it up if something gets on your windshield while you’re driving. There are special formulations for removing bugs or ice and frost as well as general purpose fluids. There’s no precise interval for replacing this fluid, but you can check it under the hood and fill up as needed.

It’s important to note though, that different washer fluid has different freeze temperatures, and if you live in the northern half of the country that encounters below-15 degree temperatures, it’s important to note that not all washer fluid is equal. Summertime washer fluid, like Bug Wash, can freeze in sub-zero temperatures, rendering your washer system useless when you most need it. Once fall comes, it’s a great idea to get any summertime fluid out, and replace it with De-icer, which is always rated into negative temperatures.

Helpful How-To’s

If it’s time to change any of your car’s fluids, shop online or go to your local AutoZone to find any fluids your vehicle needs. Our associates can help you find out which fluids need to be changed and which versions of the fluid to use for your specific vehicle.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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