Amber to dark brown and oily = engine oil. Green, orange, pink, or blue and slippery = coolant. Clear to light amber and slick = power steering or automatic transmission fluid (which turns reddish when new). Clear water with no smell in warm weather = normal AC condensation, not a leak. Dark brown-red and thin means brake fluid — the most urgent to diagnose, since it points to a failing seal in the braking system.
At a glance
| Colour | Likely fluid | Urgency |
|---|---|---|
| Clear, watery, no smell | AC condensation | Normal — no action needed |
| Amber to dark brown, oily | Engine oil | Check level; book a check within days |
| Green / orange / pink / blue | Coolant | Check level soon; don't drive if overheating |
| Reddish to brown, thin | Brake fluid | Urgent — get brakes inspected immediately |
| Red to brown, slick | Transmission / power steering fluid | Check level; book a check within days |
Why colour alone isn't always enough
Colour is the fastest first clue, but texture, smell, and where the puddle sits under the car narrow it down further. Oil is slippery between your fingers and smells faintly petroleum-like; coolant feels slightly sticky (from the glycol) and smells sweet; brake fluid feels oily but thinner, with a mild chemical smell; power steering fluid smells burnt if it's been leaking a while onto a hot component.
Fluid-by-fluid identification
Engine oil (amber to dark brown/black)
Usually drips from underneath the middle of the engine bay — a valve cover gasket, oil pan gasket, or drain plug are the most common sources. New oil is amber; used oil darkens toward black. A small drip after a car has been parked overnight is common on older engines and not automatically an emergency, but check the dipstick level before your next drive.
Coolant (green, orange, pink, or blue depending on formulation)
Coolant typically shows up near the front of the engine bay (radiator, hoses) or center-front under the car. It has a distinctly sweet smell — pets are drawn to it, which is part of why it's dangerous if left in a driveway. A coolant leak combined with a rising temperature gauge means stop driving immediately; running low on coolant is one of the fastest ways to cause serious engine damage.
Brake fluid (clear to brown, thin and oily)
Found near a wheel (caliper or wheel cylinder) or under the brake master cylinder near the firewall. Any confirmed brake fluid leak is urgent — it usually means a failing seal, and brake performance can degrade with little warning. Do not drive until it's inspected.
Transmission and power steering fluid (red when new, browning with age)
Transmission fluid tends to drip further back, roughly under the middle-to-rear of the engine/transmission housing; power steering fluid leaks are usually near the front, close to the steering rack or pump. Both are typically red or pink when fresh, turning brown as they age or overheat.
| Fluid | Typical smell | Typical leak location |
|---|---|---|
| Engine oil | Petroleum, slightly burnt if hot | Center of engine bay |
| Coolant | Sweet | Front (radiator/hoses) |
| Brake fluid | Mild chemical | Near a wheel or firewall |
| Transmission fluid | Slightly burnt, petroleum | Middle-to-rear underside |
| Power steering fluid | Burnt if long-standing | Front, near steering rack |
| AC condensation | None | Center-front, only in warm/humid weather |
A simple confirmation test
- Place a sheet of light-coloured cardboard or paper under the suspected drip overnight
- Note the colour, thickness, and smell of the mark in daylight
- Cross-check against the table above and the fluid's likely under-car position
- Check the corresponding dipstick or reservoir level to confirm which fluid is low
- If it's coolant or brake fluid, avoid driving until a mechanic confirms the source
Never assume a leak is "just condensation" if the weather is cold or dry — AC condensation only appears after the air conditioning has run in warm, humid conditions. Any puddle in cool weather deserves a proper look.
Frequently asked questions
What colour is a coolant leak usually?
Is it normal for water to drip from under my car?
How urgent is a brake fluid leak?
Can I tell transmission fluid from engine oil by colour?
What should I do if I can't identify the leak?
Sources & further reading
- NHTSA — Vehicle Maintenance Basics
- AAA — Identifying Car Fluid Leaks
- RAC — Common Car Fluid Leaks Explained
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