Open the bonnet, spot the symbol
The caps under your bonnet are marked with small standard icons, not words. Here's what each one means and where to expect it.
This page is just the "what am I looking at" reference. For the actual step-by-step on checking levels and topping each one up safely, that's over on Maintenance.
These are the six fluids and caps you'll find on almost every petrol or diesel car — some vehicles (EVs, certain hybrids) won't have all of these.
Oil can, dripping
Engine oil
Usually a bright yellow cap, often with an oil-can-shaped icon moulded straight into the plastic.
Top of the engine, fairly central and easy to spot.
Thermometer in waves, or "coolant"
Coolant
A translucent plastic reservoir tank with min/max lines on the side — you can usually see the fluid level without opening it.
Often near the radiator, sometimes labelled instead of symbol-only.
Never open when the engine's hot — it's pressurised.
Circle with an exclamation mark
Brake fluid
A small reservoir, usually near the back of the engine bay on the driver's side, often marked "DOT 4" or similar.
Level drops very slightly as brake pads wear — that's normal.
A sudden drop is not normal — get it checked, don't just top up and ignore it.
Windscreen with spray lines
Washer fluid
Usually a blue cap with a windscreen-and-jet symbol — the cheapest and easiest one to top up on any car.
Often towards the front or side of the engine bay, blue cap is the giveaway.
Steering wheel icon
Power steering fluid
Only relevant on older or hydraulic-assist cars — many modern cars use electric power steering with no fluid at all.
If your car has it, usually a small reservoir near the steering rack or belt area.
Battery symbol
Battery (12V)
Sealed on most modern cars, so there's no fluid to check — just terminals to keep clean and tight.
Usually a black box with red/black terminal caps, corner of the engine bay.
Blue filler cap, often marked "AdBlue"
AdBlue (diesels only)
A urea solution that some diesels inject into the exhaust to cut emissions. Not a fluid the engine uses — it has its own separate tank and its own dashboard warning.
Usually a blue cap beside the diesel filler, sometimes in the boot or engine bay instead.
Run out and the car will refuse to restart once it has stopped. The warning starts thousands of miles ahead — don't ignore it.
Often no cap and no dipstick at all
Gearbox / transmission fluid
Many modern gearboxes are sealed for life with nothing for you to check or top up. Where there is a dipstick, the procedure is car-specific — some need the engine running and warm.
If your car has one, the handbook will say where. If it doesn't mention one, you haven't missed it.
This is a handbook job, not a guess. Wrong fluid or wrong level can be expensive.
Clipped or screwed plastic box
Engine air filter
Not a fluid, but it lives under the bonnet and gets changed at a service. A paper element in a plastic housing that stops grit reaching the engine.
A large plastic box to one side of the engine, with a thick duct running off it.
Lid with a printed fuse diagram inside
Fuse box
Where to look when one thing has stopped working — a single window, a socket, the radio. The lid usually has a map printed on its underside saying which fuse does what.
Often in a corner of the engine bay, and frequently a second one inside the car near the driver's footwell.
Replace a blown fuse with the same rating, never a higher one. A fuse that blows again is telling you about a fault elsewhere.
Symbols vary a littleManufacturers don't all use identical icons, but they're close enough across brands that once you know the general shape (a can for oil, a windscreen for washer fluid), you'll recognise it on almost any car. If in doubt, your handbook has an "under the bonnet" diagram that names everything exactly.