How to Check Coolant and Other Fluids
Your car relies on several fluids to run, cool, brake, and clean — and they all need to stay at the right level. A quick under-hood check catches low fluid before it becomes a breakdown.
- Never open the radiator cap while the engine is hot.
- Check coolant, brake fluid, and washer fluid regularly.
- Use the correct fluid type for your specific car.
- Top up slowly and recheck to avoid overfilling.
Start with a cool engine
The golden rule of checking coolant is to do it when the engine is cold. The cooling system builds pressure when hot, and opening the radiator cap while it's hot can spray scalding coolant. Check fluids after the car has sat for a while, and never open a hot radiator cap.
Check the coolant level
Most cars have a translucent coolant reservoir with "min" and "max" lines on the side, which you can read without opening anything. The level should sit between those lines when the engine is cold. If it's low, add a 50/50 mix of coolant and water, or pre-mixed coolant, until it reaches the full line.
Use the right coolant
Coolant, or antifreeze, comes in different colors and formulations, and using the wrong type can cause corrosion or damage. Your owner's manual lists the correct type for your car — common ones include green, orange, and pink, each for different systems. Match the type rather than mixing whatever's on the shelf.
Check the brake fluid
Brake fluid lives in a small reservoir near the back of the engine bay, and it should sit between the marked minimum and maximum. If it's low, it can indicate worn brake pads or a leak — both worth checking. Never let brake fluid run low, since it directly affects your ability to stop.
Top up the washer fluid
Windshield washer fluid is the easiest one to check and fill, and it's worth keeping topped up — a dirty windshield in bad weather is a real safety hazard. Fill the reservoir with a washer fluid rated for your climate, and use a winter formula in cold months so it doesn't freeze.
Check the transmission fluid
Many cars have a transmission dipstick, similar to the oil dipstick but usually further back. Check it with the engine running, in park, and on level ground, and follow the owner's manual for the correct procedure. Some newer cars have sealed transmissions that don't need regular checks — the manual will tell you.
Know your power steering fluid
If your car uses hydraulic power steering, it has a small reservoir for power steering fluid. A low level can cause noisy or stiff steering. Check it occasionally and top up with the correct fluid if needed. Many newer cars use electric power steering and don't have this fluid at all.
Watch for leaks under the car
Fluid spots on your driveway are a clue that something's leaking. Coolant is often green, orange, or pink; oil is brown or black; and transmission fluid is reddish. Noticing and identifying a leak early lets you fix a small problem before it becomes a big one.
Make a fluids check part of your routine
You don't need to check every fluid every week, but a quick once-over every month or two catches most problems early. Pair it with your tire and oil checks, and you'll stay on top of the essentials with very little effort — and your car will thank you with reliable service.
Know the signs of low coolant
Low coolant often shows up as the temperature gauge running higher than normal, or a sweet smell from under the hood. Either is a signal to check the level — before the engine overheats. Catching it early is far cheaper than an overheating repair.
If the level drops repeatedly, that points to a leak worth finding. Topping up is a stopgap; diagnosing the cause is the real fix.
Frequently asked questions
Can I add water instead of coolant?
In an emergency, plain water works temporarily, but coolant provides antifreeze and corrosion protection. Add the correct coolant as soon as possible, and avoid pure water in cold weather.
How do I know if my brake fluid is low?
Check the reservoir's level against its markings. If it's low, have your brakes inspected — low brake fluid often means worn pads or a leak.
Why does my car lose coolant over time?
Some slow loss is normal, but a noticeable drop usually means a leak in a hose, the radiator, or the water pump. Have it checked before it causes overheating.