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These are the 8 essential car fluids you should be checking regularly

ICE vehicles need more than just gas and oil to run

Most car owners don’t realize how complicated their vehicles really are. Cars with an internal combustion engine need fluids, and lots of them, to operate smoothly. You probably know about the basics, like engine oil, gasoline, coolant, windshield washer fluid, and transmission fluid. But what about differential fluid, brake fluid, power steering fluid, and air conditioning refrigerant? All of these fluids need to be checked routinely and flushed on a regular schedule. 

technician checking under the hood of a car.
Photo by Kenny Eliason on Unsplash

Depending on your vehicle, you might need some special tools to get to these fluids if you want to replace them. But if you’re just looking to check what kind of shape they’re in, most are easy to get to. 

Since every car is different, you’ll want to follow your owner’s manual to see where you can find these fluids on your specific vehicle and what kind of fluids your car needs. 

What fluids does a car need? 

Gasoline is just one of the many fluids your car needs. Some fluids, like engine oil, transmission oil, and coolant are obvious, but there are a few other obscure ones that you may not know about. Here’s a list of the eight car fluids that you should keep an eye on:

  • Engine Oil
  • Transmission Fluid
  • Brake Fluid
  • Power Steering Fluid
  • Differential Oil/Transfer Case Fluid (4WD)
  • Coolant
  • Window Washer Fluid
  • Air Conditioning Refrigerant

Engine oil

Jug of Pennzoil engine oil being poured out with a yellow background.

This one is the simplest fluid to check. The majority of new cars on the market have a dipstick with an orange or yellow top that can be pulled out. Once the dipstick is out, you’ll want to check the dipstick to see what color the engine oil is – a darker, black color signifies oil that needs to be changed, while a lighter, caramel-colored oil is relatively new. 

It’s best to wipe the dipstick with a clean white rag to double-check the color and insert it back into the dipstick tube, before wiping off the oil a few times. You’ll want to keep an eye on the level, which is located at the bottom of the dipstick, to make sure that the engine has enough oil.

It’s best to check engine oil once the car has had time to fully warm-up, but you’ll want to keep the engine off when completing the test. 

Depending on what kind of oil you use in your car, you’re looking at changing engine oil every 3,000 miles for conventional oil to 10,000 miles for full synthetics. 

Transmission fluid

Like the engine oil dipstick, the transmission fluid dipstick is located underneath the hood. The dipstick for the transmission is located further back in the engine bay and typically has a different color or a transmission symbol on the actual dipstick. If you can’t find a dipstick, don’t fret. Some modern vehicles have a transmission that’s sealed for life from the factory and don’t require new fluid. 

Checking transmission fluid requires the vehicle to be warmed up and running at idle to be checked. With the dipstick pulled out, you’ll want to check the level at the bottom to ensure that there’s enough fluid in the transmission, and clean the dipstick with a white rag or towel to check the color. Healthy transmission fluid will have a red or pink color, while fluid that needs to be changed will have a brown or black look. 

Some vehicles require owners to change the transmission oil every 30,000 miles. 

Brake fluid

Your car’s brake fluid resides in a reservoir underneath the hood. Usually, it’s marked by a black lid with a circular image. It’s usually located close to the firewall. Checking the brake fluid is simple. All you have to do is peek into the reservoir, see what color the brake fluid is, and make sure it’s close to the “full” line. New brake fluid is almost translucent with a golden tint to it. 

If your brake fluid is dark brown or black, it needs to be flushed. Low brake fluid is a sign that you could have a leak or that your brakes need to be replaced. Be sure to follow your owner’s manual to use the specific type of brake fluid that your automaker recommends. 

Brake fluid mostly depends on driving habits. If you drive a performance vehicle and stomp on the brakes a lot, you’ll want to flush your brake fluid multiple times in a year. For the majority of other drivers, brake fluid should be changed every two years. Owners can purchase test strips to check the quality of the brake fluid. 

Power Steering fluid

The reservoir for the power steering system is also located underneath the hood. Most of the time, the power steering reservoir is a darker color than the brake fluid reservoir and the black cap usually has “Power Steering” written on it. Some power steering reservoirs are clear, which means checking it just requires you to look at the color and fill level. 

For dark reservoirs, there’s a little dipstick that’s attached to the cap. You can check the level of the fluid by looking at the leveler on the dipstick. Checking the quality and age of the fluid requires a white rag that you can clean the dipstick with. Power steering fluid is usually red or pink, so anything brown or black needs to be replaced. 

Power steering fluid is something that differs depending on the automaker, but a good rule of thumb is every 30,000 miles. If your car has an electric steering system, you don’t have to worry about changing the power steering fluid. 

A jug of Prestone predicted 50/50 antifreeze/coolant in front of a yellow classic pickup truck in a garage.


Coolant, as its name implies, helps keep your engine cool and often goes overlooked as it’s out of sight. To check your antifreeze, you’ll have to order an antifreeze coolant tester, which looks like a funky turkey baster. Then, you’ll have to open the radiator cap – only do this when the car is cool! – suck some coolant with the tester, and check the reading. You can also look at the bottom of the radiator cap and inside the radiator to check for signs of sludge or gunk. Some cars have a coolant reservoir that you can check instead of the radiator. 

Different automakers use different types of antifreeze, which can make diagnosing bad antifreeze difficult. You’ll want to follow your owner’s manual to get the correct type of coolant for your vehicle. Most coolant needs to be replaced every three years or 36,000 miles. 

Air conditioning refrigerant 

Checking air conditioning refrigerants is tricky because it requires special tools. One workaround for this is to purchase a recharge kit, which usually comes with an easy-to-use gauge. These kits require you to attach a coupler to the low-pressure port of your car’s AC system and read the gauge when the air conditioning is running. That’s it! Mostly. There are a few more things you have to do, but it’s that simple. 

A good rule of thumb is to check your AC system annually. Skipping a check could mean going without air conditioning in the summer. If you find that your car’s air conditioning system needs to be recharged consistently, you can check for leaks with a special refrigerant with some UV dye in it, which will glow a certain color under UV light. 

Differential oil and transfer case fluid

Differential oil and transfer case fluid are some of the hardest fluids to check. Most of the time, these fluids are locked away behind fill and drain bolts that need to be removed to check the quality and level of the fluid. We don’t recommend removing either of these unless you know what you’re doing, have extra fluid on hand, and a pump to put new fluid in. For these, it’s best to stick with the automaker’s schedule and regularly check for leaks. Differential oil and transfer case fluid should usually be replaced every 30,000 miles for conventional gear oil and 60,000 miles for synthetic oil. 

Mechanic working underneath a black classic muscle car in a garage.

What is the cost to change all fluids in a car? 

When it comes to changing all the fluids in your car, the most expensive part of the job is the fluids themselves. Some vehicles require pricey fluids with extra additives that can add up while using synthetics that will last longer and will drive up the initial cost. With a manual and some help from YouTube, changing all the fluids in your car is a straightforward DIY job, similar to changing your engine’s air filter. If you head to a shop, you could be looking at spending anywhere from $500 to $1,000 to get all of your car’s fluids flushed. 

Changing all of the fluids in your car may seem like a difficult task, but checking them is usually straightforward. To get into a groove, you’ll want to check all these fluids every year to stay on top of them — especially before heading on a road trip. When the fluid gets old, it loses its helpful properties and puts components in danger of failing. Routinely checking your fluids may seem like a tedious task, but replacing them every few years is far more affordable than replacing the components they protect. Spend some time checking and replacing the fluids in your car regularly and it will reward you with more years of trouble-free ownership.

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