Inside Your Engine Bay: What Every Driver Should Recognise

For many drivers, lifting the bonnet can feel intimidating. Wires, caps, hoses, metal parts — it's easy to assume you need to be a trained mechanic to understand what's going on. But here's the truth: you don't need a toolbox or overalls to recognise key components inside your engine bay — and knowing the basics can save you money, stress, and even an MOT fail.

Whether you're a seasoned car owner or just got your first set of keys, this guide will help you confidently identify what’s under the bonnet, what’s normal, and when something needs a professional look.

? First Things First: Open the Bonnet Safely

Before we dive in, always check your owner's manual for how to safely open the bonnet on your specific vehicle. Most UK cars have a bonnet release lever inside the cabin (usually near the footwell), followed by a secondary latch at the front of the car. Make sure the engine is off and the area is well-lit. When checking anything under the bonnet, always let the engine cool first to avoid burns or injury.

? 1. Battery

Your car’s battery powers everything electrical — from the ignition to your headlights. You’ll usually find it in a black plastic casing with two cables: red (positive) and black (negative).

A healthy battery should have clean, tight terminals and be free of bulges or corrosion. Corrosion often looks like a white or green crusty residue on the terminals. If you see this, it’s worth getting it checked professionally.

What to look for:

• Clean, tight terminals (no white or green corrosion)

• No bulging or cracks on the casing

• Securely mounted

? Also read: Driving With Confidence – How Our Diagnostics Can Save You Money

?️ 2. Oil Dipstick & Filler Cap

Oil lubricates your engine. The dipstick lets you check the level, and the filler cap is where you add oil if it’s low. To check your oil, remove the dipstick, wipe it clean, reinsert it fully, then pull it out again to check the level.

If the oil is very dark, sludgy, or smells burnt, it’s due for a change. Also check around the oil filler cap — if you see a white or milky residue, it could be a sign of moisture mixing with oil, which may suggest condensation from short journeys or, in some cases, a more serious issue like a blown head gasket. If in doubt, get it inspected.

What to look for:

• Clean dipstick with a clear ‘min’ and ‘max’ marking

• Oil should be amber to brown (not thick or black)

• Milky residue around the filler cap could indicate moisture or internal issues

• Filler cap usually says ‘OIL’ and may have a small oil can icon

? If you're unsure where to add oil, refer to your car’s manual — but most caps are clearly marked and located near the engine block.

? 3. Coolant Reservoir

The coolant (or antifreeze) keeps your engine at the right temperature. The reservoir is usually a clear plastic container with coloured fluid (pink, green or blue). It circulates through the engine and radiator to prevent overheating or freezing.

A sudden drop in coolant level can indicate a leak. Never open the coolant cap while the engine is hot — the system is pressurised and could cause scalding.

What to look for:

• Fluid between ‘min’ and ‘max’ markings

• No crusty residue or leaks around the cap

• Cap secured tightly

? 4. Brake Fluid Reservoir

Essential for stopping power, the brake fluid reservoir is usually located near the back of the engine bay, closer to the driver’s side. Brake fluid absorbs moisture over time, which can reduce braking performance.

If your brake pedal feels spongy or your stopping distance has increased, poor fluid could be to blame.

What to look for:

• Light yellow to golden fluid

• Fluid between the ‘min’ and ‘max’ lines

• Cap may have a warning symbol or say ‘DOT 4’ (or similar)

? Why Brake Fluid Needs More Attention Than You Think

?️ 5. Air Filter Housing

The air filter ensures clean air enters your engine. It’s usually housed in a black box with clips or screws, near the front or side of the engine bay. A dirty or clogged filter can lead to reduced performance and increased fuel consumption.

Replacing an air filter is one of the easier DIY jobs for many car owners.

What to look for:

• Casing should be closed and secure

• Air filter (if inspected) should be light-coloured — not black or clogged

? 6. Drive Belts (Auxiliary/Serpentine Belt)

These long rubber belts drive your alternator, water pump, and other components. You can usually see them on the side of the engine and they’re critical for engine operation.

Inspect the belts for cracks, fraying, and glazing — which is a shiny, smooth appearance on the belt’s surface. Glazing happens when a belt becomes too hot or worn, reducing grip and causing slippage. If you hear squealing noises or see visible wear, it's time to have them checked.

What to look for:

• No cracks, fraying or glazing (shiny surface)

• Good tension (not overly loose or tight)

? 7. Fuse Box

The fuse box protects your car’s electrical circuits. It's often located near the battery or inside the cabin. Under the bonnet, it’s typically a black box labelled ‘FUSE’ or similar.

Fuses can blow if there’s a short or surge in the circuit. They’re inexpensive to replace but should be matched with the correct amperage.

What to look for:

• No loose connections

• Clean, dry housing

• Fuse diagram inside the lid can help identify issues

? 8. Washer Fluid Reservoir

This one’s easy. Look for the blue cap with a windscreen symbol. It's the simplest top-up job but a critical one — washer fluid is required by law for an MOT.

In winter, use proper screenwash to prevent freezing.

What to look for:

• Fluid present (especially in winter)

• Cap secured

? Building Confidence Under the Bonnet

If you’re a new driver or someone who’s never looked under the bonnet before, the key is not to be afraid. You’re not expected to fix things — just to know what looks right, and when to seek help.

Learning to identify the basics isn’t just about car knowledge — it’s about peace of mind and proactive care. Knowing what’s under your bonnet means you can spot potential problems early, save money, and feel more confident speaking to a mechanic.

At Brede Garage, we’re always happy to explain what’s going on inside your engine bay. Whether you're prepping for an MOT or just want to learn more about your car, we’re here to help.

? Book a vehicle inspection or diagnostic check and let us help you build confidence — one bonnet lift at a time.