What Fluids Should I Top Off?

While there are several fluids in modern gas-powered cars (and some in electric vehicles) that can be checked and topped off, many would only be low if there’s a leak in that system; only a few normally get low just through use. Which ones should be topped off? Check out our list below.

Fluids found in gas cars are listed below, with those that should be most frequently checked at the top. For anything you can’t check just by looking — or if you need to add fluid — have a rag handy and wear gloves as well as safety glasses.

Fluids That Should Be Most Frequently Checked

Brake Fluid

This is not only very important, but it can get low over time as your brake pads wear. Thankfully, it’s often contained in a translucent reservoir so you can visually check the level.

Note that brake fluid is very corrosive, so you don’t want to spill it. It also easily absorbs water — which is bad — so you want to make sure it’s coming from either a new bottle or one that’s been tightly sealed immediately after opening.

Windshield Washer Fluid

This is another important fluid; when you need it … you need it. If you have a rear wiper/washer, you may have a second tank in back. Note that it’s not uncommon for the plastic tanks to crack and leak, which is another reason to check it periodically.

What keeps washer fluid from freezing in cold weather is usually methanol (a poisonous alcohol), which can evaporate in summer heat — which means the “Good to -20 degrees F” washer fluid you put in last year might not be good anymore. It’s thus a good idea to fill your tank in late fall with fresh washer fluid, preferably the “Good to -35 degree” kind (often purple). After doing so, run the washer for a bit to clear the lines of old fluid.

Engine Oil

While newer cars often don’t need to have oil added between scheduled changes, some might, and older ones certainly may. So it’s a good idea to check the oil level periodically — even on newer cars.

However, it’s really important to do it right. Before checking, the engine should be off for at least five minutes to allow all the oil that circulates through the engine to drain back into the oil pan. It’s also important that the oil not be overfilled, as that can result in engine damage. Also, different cars use different “weights” of oil (10W-30 is a popular one), so make sure you get what the manufacturer of your vehicle recommends.

Fluids That Shouldn’t Be Low but Might Be Due to Leaks

Coolant

Sometimes referred to as “antifreeze” (which technically makes up only about half of your coolant mix, the other half being water), this fluid can usually be visually checked in the translucent coolant overflow tank. However, you typically shouldn’t need to add much unless there’s a leak in the system. If the fluid in the tank is really low or you want to be thorough, you could also remove the radiator cap, but you have to be certain that the radiator is cold, or scalding coolant could spray out.

A cautionary note: Antifreeze used to always be green, but there’s now also an orange version — and maybe other colors — and you need to use the proper kind; consult your owner’s manual.

Automatic Transmission Fluid

While this used to be a fairly easy and fundamental fluid to check, some cars don’t include a transmission-fluid dipstick. There might be a plug you can remove, but it’s often tough to find and get to.

If you have a dipstick, consult your owner’s manual for the proper procedure to check the fluid level. As with engine oil, it shouldn’t be overfilled. If you need to add some, check to make sure what kind you need, as there are several, and they shouldn’t be interchanged.

Power-Steering Fluid

Power-steering fluid should only be low if there’s a leak, but it’s still a good idea to check it periodically. This is another case where there are different types for different vehicles, so check which kind you need.

Fluids Only Found on Certain Cars

Differential Fluid

This usually only applies if you have a separate front or rear axle, which is typically the case with rear-wheel-drive, all-wheel-drive or four-wheel-drive vehicles. You usually have to get under the vehicle to check it, but it should only get low if you have a leak.

Manual Transmission Fluid

This only applies if you have a manual transmission, and it shouldn’t get low. If you have a manual transmission, you might also need to check …

Clutch Fluid

Typically, clutch fluid is contained in a reservoir much like the one for brake fluid (so make sure you check the right one), this can get low through use or a leak.

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