Leaks
How to Spot and Identify Common Car Fluid Leaks
Every fluid in a car is a different colour, sits in a different place and matters a different amount. Two minutes of looking will usually tell you which one you have and how worried to be.
What this guide covers
The Identification Table
| What you see | Most likely | How urgent |
|---|---|---|
| Clear, watery, front passenger side after AC use | Air conditioning condensate | Normal |
| Green, pink, orange or blue, slightly slimy | Coolant | Urgent |
| Dark brown to black, thick, slippery | Engine oil | Depends on rate |
| Reddish, thin, slippery | Transmission or power steering fluid | Soon |
| Clear to light brown, oily, near a wheel | Brake fluid | Stop driving |
| Dark, near one wheel only | Leaking damper | Book it in |
| Blue, watery | Windscreen washer fluid | Harmless |
| Petrol smell, evaporates quickly | Fuel | Stop driving |
If you cannot confidently identify it and it is anywhere near a wheel, treat it as brake fluid until proven otherwise. That is the one where being wrong has immediate consequences.
The Test That Answers Everything
Lay a sheet of white or light-coloured cardboard under the car overnight, positioned under where you saw the patch.
In the morning you have colour against a clean background, exact position, and a sense of volume. You also learn whether it is your car at all, which in shared parking is not a trivial question.
Position narrows things considerably. Front and centre points at engine oil or coolant, near a wheel points at brakes or a damper, and mid-car often means transmission.
Fluid by Fluid
Air conditioning condensate: the false alarm
Clear water under the front passenger area after running the air conditioning is the system draining moisture out of the cabin air.
In this climate it can be a surprising amount. It is completely normal and it is the single most common thing owners mistake for a fault.
Coolant: the urgent one
Brightly coloured and faintly sweet-smelling. A cooling system is sealed and does not consume coolant, so a falling level always means a leak.
Treat this as more urgent than an oil leak of similar size. See common causes of coolant leaks.
Engine oil: measure before worrying
Dark and thick. The question is not whether it drips but whether the level is dropping, and how fast.
See is your car leaking oil to confirm it, and how long you can drive with an oil leak for urgency.
Transmission fluid: do not ignore
Reddish, thin and slippery, usually mid-car. Automatic gearboxes are sensitive to level, and running one low causes damage quickly.
This deserves attention sooner than an equivalent oil leak.
Brake fluid: stop
Clear to light brown, oily, near a wheel or under the pedal area.
Brakes are hydraulic and a leak means the system can lose pressure. If the pedal also feels soft or sinks, do not drive the car.
Power steering fluid
Often reddish like transmission fluid, but at the front near the steering rack.
Heavy steering, or a whine when turning at low speed, points here.
Damper fluid
A damper that is wet down one side has failed internally. It is not a spill, it is the damper telling you it has stopped working.
Dampers are replaced in pairs so the axle behaves consistently.
Two Things Not to Do
- Do not clean the engine before diagnosis. The trail is how the source gets found, and washing it away means waiting for it to come back.
- Do not rely on stop-leak products. They circulate through the whole system and cannot target the leak you meant. Acceptable to move a car, not to fix one.
Getting It Traced
Fluids travel once they escape, so where it lands is often not where it came from. That is the whole difficulty with leak diagnosis.
Exotic Auto Services degreases, uses UV dye where needed and pressure tests the cooling system, which turns guesswork into an answer in one visit.
For general symptoms, see common car problems sorted by what you notice.
Frequently Asked Questions
What is the clear liquid dripping under my car?
If it is under the front passenger area and appears after using the air conditioning, it is condensate: the system removing moisture from cabin air. In this climate it can be a surprising amount of water and it is completely normal. If it is clear, oily and near a wheel, that is a different matter and should be treated as brake fluid.
How do I know what colour a leak is?
Lay white or light-coloured cardboard under the car overnight. Against a clean background the colour is obvious, and you also get the exact position and a sense of volume. It also confirms whether the leak is from your car at all, which in shared parking is worth establishing first.
Which car leaks are the most urgent?
Brake fluid and fuel mean stop driving. Coolant is urgent because an engine that overheats is a far larger repair than the leak. Transmission fluid should be dealt with promptly because gearboxes are sensitive to level. Engine oil depends on how fast you are losing it, and washer fluid is harmless.
Is a wet shock absorber a leak I should worry about?
It means the damper has failed internally rather than spilled something. A damper that is no longer controlling the spring lengthens braking distances and lets the tyre lose contact with the road, so it is worth replacing, and they are replaced in pairs so the axle behaves consistently.
Should I use a stop-leak product?
Only to get a car to a workshop. These products circulate through the entire system and cannot target the specific leak, so they lodge in narrow passages such as a heater matrix or a thermostat, and in the case of engine oil they swell every seal rather than the failed one. They buy time and cost capacity.
