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The Ultimate Guide to Car Fluids

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The Key To Proper Vehicle Maintenance Is Regular Fluid Changes. Here’s Everything You Need To Know About The Fluids In Your Car.

Fluids are literally the lifeblood of your car with most of them providing lubrication for major components. But properly caring for your car goes beyond basic oil changes and topping off the windshield washer reservoir. At FIXD, our mission is to make car care as simple, affordable, and stress-free as possible, so we’ve put together this ultimate guide to car fluids so that you know what fluids to look for, how often to change them, and if it’s worth the cost to do it yourself!

There are 10 car fluids that require regular attention on your car. Check them all out below or use the table of contents to navigate to the car fluid you have questions about. Even if you don’t plan on changing these fluids by yourself, this is still important information to have when taking your car to a repair shop.


Engine Oil

Change engine oil about every 3,000 to 10,000 miles depending on your vehicle.

Even for non-DIYers, engine oil might be the most commonly recognized item of the car fluid guide. This fluid lubricates the engine’s internals that include the pistons, crankshaft, and camshaft, and regular oil changes are important to ensure that your engine stays running properly for years.

Failing to change the oil can lead to a breakdown in the viscosity, which can limit its effectiveness as a lubricant and lead to damage that includes anything from engine failure to sludging. If the engine has an oil leak or is burning oil, this can lead to the engine not having enough oil causing expensive internal damage. 

How often to change engine oil: 3,000 – 10,000 miles

Here’s a guide for how to change your car’s oil as well as a breakdown of how much an oil change should cost.

Engine Coolant

use a funnel to fill radiator with new engine coolantChange engine coolant about every 30,000 depending on your vehicle.

While oil keeps the engine’s internal components properly lubricated, the coolant ensures that the engine runs at optimal temperatures. Failing to properly service the engine coolant can cause damage to the engine as well as the water pump, radiator, and even the heater core. When changing the coolant, it’s also important to inspect the radiator hoses. 

How often to change engine coolant: 30,000 miles

Check out the how-to guide for changing the engine coolant and a breakdown for how much it should cost to change the coolant.

Transmission Fluid

Change transmission fluid about every 50,000 depending on your vehicle.

Whether you have an automatic or manual transmission, both have fluids that must be changed at regular intervals. Manual transmissions are much easier to work with when it comes to DIY fluid changes, but advanced-level DIYers can tackle a fluid and filter change on an automatic transmission.  

How often to change transmission fluid: 50,000 – 100,000 miles

Here’s how to change the fluid in an automatic transmission, and here’s how to perform this service on a manual gearbox.

Power Steering Fluid

Power steering fluid reservoirChange power steering fluid about every 50,000 depending on your vehicle.

While most modern vehicles are using electric motors for the power steering system, the majority of cars on the road still use a system filled with hydraulic fluid. This fluid breaks down over time, and it can lead to noises, leaks, or excessive wear on the serpentine belt

How often to change power steering fluid: 50,000 miles

Check out the how-to guide for changing power steering fluid as well as a breakdown of how much a power steering fluid change should cost.

Transfer Case Fluid

Change transfer case fluid about every 30,000 depending on your vehicle.

On vehicles equipped with all- or four-wheel drive, a transfer case (also known as the t-case) attaches to the transmission, and it splits the power between the front and rear axles. Changing the transfer case fluid is usually as simple as draining and refilling the transfer case in a similar fashion to how you change manual transmission fluid. 

How often to change transfer case fluid: 30,000 miles

Here’s more information on transfer case fluid, including how to change it.

Differential Fluid

closeup view of the differential coverChange differential fluid about every 30,000 to 60,000 depending on your vehicle.

Cars equipped with rear-, all- or four-wheel drive utilize axle differentials, which feature a fluid that must be changed regularly. Not performing this service can lead to excessive wear, noise, and/or damage to the axle’s internal gears. Fortunately, this is an extremely easy (albeit smelly and messy) job for DIYers to perform. 

How often to change differential fluid: 30,000 – 60,000 miles

Here’s what you need to know about changing the differential  fluid, and here’s how much a differential fluid change should cost.

Brake Fluid

check brake master cylinder fluid reservoirChange brake fluid about every two years depending on your vehicle.

Generally speaking, you don’t have to worry about brake fluid too often except for topping off the reservoir under the hood when the brake light comes on. Flushing the brake fluid is recommended at normal service intervals, and the brake fluid system must be bled when calipers or wheel cylinders are replaced. 

How often to change brake fluid: two years

Windshield Washer Fluid

Windshield washer reservoirRefill windshield washer as needed; some cars have a light that comes on when this fluid is low.

Perhaps one of the most overlooked fluids on your vehicle is the windshield washer fluid… until you need to spray bugs or dirt off the windshield. Most cars will have a low washer fluid light to alert the drivers, and keeping this fluid topped off likely means you should be able to change the wiper blades less frequently.

How often to change windshield washer fluid: fill the reservoir as required

Here’s what you need to know about windshield washer fluid.

Diesel Exhaust Fluid

Diesel exhaust fluid bottleRefill diesel exhaust fluid as needed; a warning light will illuminate when this fluid is low.

Diesel exhaust fluid (DEF) is a lot like filling your fuel tank in that this fluid needs to be added regularly instead of changed. Failing to add DEF to a diesel vehicle could result in the vehicle not running, but that is due to computers shutting the engine down. No damage will be caused by an empty DEF tank. 

How often to change diesel exhaust fluid: fill the tank as required

Here’s all you need to know about diesel exhaust fluid.

Fuel Tank

Speaking of the fuel tank, you can’t overlook the one fluid that makes your vehicle run. Whether it’s a gasoline or diesel vehicle, the only reasons you would ever need to drain the fuel tank would be contaminated/old fuel or to perform maintenance or repairs such as the replacement of an in-tank fuel filter or fuel pump. 

How to Dispose of Old Car Fluids

For DIYers, this car fluid guide is meant to breakdown all of the fluids on modern vehicles, but all of these fluids are hazardous and should only be disposed of properly. Engine oil is the easiest to deal with since most auto parts stores will recycle this oil for you at no charge, but you should also make sure to let all of the oil drain out of the oil filter before throwing it away. 

All other vehicle fluids require special recycling and should not be poured in the grass or down the storm drain. Contact your local city or county government to find out how to properly and responsibly dispose of used vehicle fluids, or if you do occasional fluid changes as DIY maintenance, you could try to find a local shop that might let you recycle small amounts of fluid at no charge.


So there you have it. Whether you’re changing fluids or just topping them off, this guide to car fluids is all you need to know to perform regular maintenance that keeps your vehicle running smoothly.

Be sure to get the FIXD Sensor and free app today so that you will never miss important maintenance (like fluid changes). The free app not only scans your car for check engine problems and translates them into simple terms, but it also alerts you when it’s time for routine maintenance, displays live engine data, helps you find reliable repair shops, and much more. Learn more at fixdapp.com.

Other Common Car Repair Costs Transmission oil change cost Car AC recharge cost Average cost for front brake job Cost to replace spark plugs Timing chain replacement

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.

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About the Author

Jeffrey N. Ross

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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