How to Check and Top Up Your Car's Fluids

Checking your car's fluids takes about ten minutes and catches problems early: a slow oil leak, a coolant loss that would end in overheating, brake fluid dropping because pads are worn. You do not need tools beyond a rag and a flashlight. This guide covers each fluid, how to read the level, what to top up with, and what the warning signs look like.

Do a full check once a month and before long trips. Your owner's manual has the exact locations, fluid specifications and capacities for your car; when it differs from general advice here, follow the manual.

• Park on level ground. A slope can make levels read high or low.
• Know which checks need a cold engine (coolant, and oil on most cars) and which need a warm engine (automatic transmission fluid on many cars). The sections below say which.
• Open the hood and find the caps. Most are labeled with symbols and are often yellow or another bright color.
• Have a clean, lint-free rag or paper towel, a flashlight and a funnel.

Oil is the most important check, and many engines consume some oil between changes, especially as they age.

How to check

1. 1With the engine off (wait about 5 to 10 minutes after driving so oil drains back, or check cold, as your manual specifies), pull out the dipstick. It usually has a yellow or orange loop handle.
2. 2Wipe it clean, push it fully back in, and pull it out again.
3. 3Read the level: the oil should be between the two marks (often labeled MIN/MAX, L/H, or a crosshatched area).
4. 4Look at the color and feel. Amber to dark brown is normal. Milky or foamy oil can mean coolant contamination; gritty oil or a strong fuel smell also needs a mechanic's attention.

Some newer cars have no dipstick. They show the oil level in the instrument cluster or infotainment menu; the manual explains how to read it.

Topping up

• Use the viscosity grade and specification in your manual, such as 0W-20 meeting a specific API or manufacturer standard. See synthetic vs conventional oil.
• The distance between the two dipstick marks is often about one quart, but it varies; check the manual.
• Add half a quart at a time through the filler cap on top of the engine, wait a minute, and recheck. Do not overfill; too much oil can foam and cause damage.

How often to change it is a separate question; see oil change interval.

Coolant keeps the engine at the right temperature and protects it from freezing and corrosion.

How to check

1. 1Make sure the engine is completely cold.
2. 2Find the translucent coolant reservoir (overflow tank), usually near the radiator, with MIN and MAX (or COLD/HOT) marks.
3. 3The level should be between the marks when cold.

Topping up

• Use the coolant type specified in your manual. Coolant chemistries differ (and colors are not a reliable guide), and mixing types can reduce protection.
• Many coolants are sold premixed 50/50 with water; concentrate must be diluted as the label directs.
• Fill to the line, not above it.

If you keep having to add coolant, there is a leak or an internal problem. Look for drips, crusty residue around hoses and the radiator, a sweet smell, or white exhaust smoke. Long-term replacement is covered in coolant flush: when and how.

Brake fluid transmits pedal pressure to the brakes. It should never need regular topping up.

How to check

1. 1Find the brake fluid reservoir, usually on the driver's side near the firewall, on top of the master cylinder. It is translucent with MIN and MAX marks.
2. 2Check the level through the side without opening it.
3. 3Look at the color. New fluid is clear to light amber; it darkens with age and absorbed moisture.

What the level tells you

• The level drops slowly as brake pads wear, because the caliper pistons move outward. A level near MIN can mean pads are due; see when to replace brake pads.
• A sudden drop, a soft or sinking pedal, or wetness around a wheel means a leak. Do not drive until it is inspected.

Topping up

• Use only the type on the cap or in the manual, commonly DOT 3, DOT 4 or DOT 5.1. Never use DOT 5 (silicone) in a system not designed for it.
• Wipe the cap before opening so dirt does not fall in, use fluid from a sealed container, and close it promptly; brake fluid absorbs moisture from the air.
• Avoid spills: brake fluid damages paint.

Brake fluid needs replacing on a time schedule on many cars, commonly every 2 to 3 years; see brake fluid flush.

Many modern automatic transmissions are sealed and have no dipstick; checking them requires a lift and a specific procedure. If yours has one:

1. 1Most automatics are checked with the engine warm and running, in Park (some specify Neutral), on level ground. Follow the manual exactly.
2. 2Pull the dipstick, wipe, reinsert, pull again.
3. 3Read the level against the HOT or COLD marks as appropriate.
4. 4Fluid should be red to light brown and smell normal. Dark, burnt-smelling fluid, or metal particles, needs a professional look.

Use only the exact fluid specified; the wrong transmission fluid can cause shifting problems. Manual transmissions are checked at a fill plug, usually by a shop. Service intervals are covered in transmission fluid change interval.

Many newer cars use electric power steering with no fluid at all. If yours has a hydraulic system:

1. 1Find the reservoir, often labeled with a steering wheel symbol.
2. 2Check the level against the marks on the side or on the cap's dipstick; some are marked for HOT and COLD.
3. 3Top up only with the fluid in your manual. Some cars use automatic transmission fluid, others a specific power steering fluid.

A whining noise when turning or stiff steering can mean low fluid or a leak.

• Washer fluid: the reservoir cap usually shows a windshield symbol. Fill it to the neck. In winter, use a fluid rated for freezing temperatures. Do not use plain water in cold climates, and never use antifreeze.
• Diesel exhaust fluid (DEF): diesel vehicles with SCR systems have a separate DEF tank, usually with a blue cap. The car warns you when it is low; running out can limit engine power.
• Hybrids and EVs: many have separate coolant loops for the battery and power electronics. Check the manual; some are not owner-serviceable.

Place a piece of cardboard under the engine overnight to see what is dripping and where.