Car basics · Easy · about 10 minutes

Check Coolant, Brake Fluid, and Washer Fluid

Besides oil, your car needs a few other fluids: coolant so the engine doesn't overheat or freeze, brake fluid so the brakes work, and washer fluid so you can see. Most sit in see-through tanks with marks on the side, so a quick look tells you if one is low.

When to teach it: Watch from about 8, help from about 10, do it alone from about 13.

You'll need

Owner's manual (it shows where each tank is and which fluids to use)
The exact coolant and brake fluid your manual lists, if you need to add any
Windshield washer fluid
A clean rag
A funnel

Before you start

Park on level ground with the engine off and cold.
Never open the radiator cap when the engine is hot. Hot coolant and steam can spray out under pressure.
Keep coolant and washer fluid in their original containers with the caps closed tightly, out of sight and reach of children and pets.

Step by step

Tick each step as you go if you like; ticks stay on this device.

Find the tanksOpen the hood and use your owner's manual to find the coolant reservoir, brake fluid reservoir, and washer fluid tank. The coolant reservoir is a see-through plastic tank, often near the radiator. The brake fluid reservoir usually sits toward the back of the engine area on the driver's side.
Check the coolantLook at the side of the coolant reservoir without opening it. The level should be between the low and full marks. On some tanks, the marks are labeled hot and cold.
Top off coolant if lowIf it's below the low mark, add the coolant your manual lists to the reservoir, up to the mark but not higher. Leave the radiator cap alone.
Check the brake fluidWipe around the brake fluid cap so dirt can't fall in. The level should be between the MIN and MAX marks on the side of the reservoir.
If brake fluid is lowBrake fluid drops a little as the brakes wear. If it's near or below the low mark, have a shop inspect the brakes soon. Use only the brake fluid your manual lists, and never mix types.
Fill the washer fluidOpen the washer fluid cap and fill the tank to the top. Where temperatures drop below freezing, use a winter washer fluid that resists freezing.
Clean up and closeWipe up any drips right away, tighten every cap, and close the hood.
Watch for repeatsIf you find yourself adding coolant or brake fluid often, have a shop look for a leak.

Chemistry

How it works: How antifreeze works in winter and summer

Plain water freezes at 32 °F and boils at 212 °F, and both are a problem in an engine. Water that freezes in a cold engine can crack it. Water that boils turns to steam and stops cooling.

Coolant is a mix of water and antifreeze, which usually contains ethylene glycol. When something is dissolved in water, its particles make it harder for water molecules to line up into ice, so the mix freezes at a lower temperature. They also make it harder for water to escape as vapor, so the mix boils at a higher temperature. Chemists call these colligative properties: they depend on how many particles are dissolved, not on what kind they are.

More antifreeze gives more protection, up to a point. One Kia owner's manual says a half-and-half mix protects down to about −31 °F, and it warns against using more than 60% or less than 35% antifreeze. Your manual lists the right coolant for your car.

Brake fluid has its own chemistry problem. It slowly soaks up moisture from the air, and that lowers its boiling point. That's one reason to keep the cap closed and use fluid from a sealed bottle.

drop in freezing point = K_f × m (K_f is a set number for water; m is how much is dissolved)

Try it: Fill two paper cups with the same amount of water. Stir a few spoonfuls of table salt into one. Put both in the freezer and check every 30 minutes. The plain water freezes first, while the salty water stays slushy longer because the dissolved salt lowers its freezing point. Never experiment with real antifreeze; it's poisonous.

Keep learning: Science

Teaching it to your kids

Have your child find each tank using the pictures in the owner's manual.
Ask them to read each level out loud: below, between, or above the marks.
Talk about why the radiator cap stays closed when the engine is hot.
Do the salt-water freezer test together before your first winter check.

Tips

One Kia manual says to check coolant and its freeze protection at least once a year, at the start of winter, and before a trip somewhere colder. Check what your manual says.
Clean around caps before you open them so dirt doesn't get in.
Don't let brake fluid touch the car's paint. It can damage it.
Don't overfill. Too much fluid can be as harmful as too little.

Common mistakes

Mistake	Instead
Opening the radiator cap on a hot engine	Read the see-through reservoir instead, and only when the engine is cold.
Using the wrong coolant or brake fluid	Use only the type your manual lists, and don't mix types.
Using summer washer fluid in freezing weather	Switch to a winter washer fluid that resists freezing.
Storing fluids in drink bottles	Keep them in their original containers. People sometimes drink these fluids by mistake.

Safe habits

Never open the radiator cap while the engine is hot.
Antifreeze and washer fluid are both poisonous. Antifreeze tastes sweet, which can attract children and animals.
Wipe up coolant spills and leaks right away.
Keep caps tightly closed and store bottles out of sight and reach.

When to call a pro

If the brake fluid is near or below the low mark, have a shop inspect the brakes for wear or leaks as soon as possible.
If you need to add coolant often, have the cooling system checked.
If the engine is overheating or steaming, don't open the radiator cap. Let it cool and get help.

Sources

Free how-to guides for families, with nothing to earn, pass or send in. They follow U.S. rules and sources; your owner's manual, product labels and state and local rules come first.