Published 10 Jul 2026 · By AI-Diagnostics-Pro · 8 min read
Engine bay checks are a common part of the Show Me Tell Me section of the UK driving test. The examiner may ask you to check the oil, coolant, brake fluid, or power steering fluid — or explain how you'd do it.
These checks are also essential for keeping your car MOT-ready and preventing breakdowns. Here's how to perform each one correctly.
Always check with the engine cold: Most fluid checks should be done with the engine off and cool. Hot coolant can be pressurised and dangerous to open.
1. Engine Oil Level Check
The engine oil lubricates your engine. Running low can cause serious damage.
How to check:
Park on level ground and turn off the engine
Wait 5 minutes for oil to settle back into the sump
Locate the dipstick (usually has a yellow or orange handle)
Pull the dipstick out completely and wipe it clean with a cloth
Reinsert the dipstick fully, then pull it out again
Check the oil level — it should be between the minimum and maximum marks
If oil is low: Top up with the correct grade of oil for your vehicle (check the handbook). If you're topping up frequently, there may be a leak or engine issue — get it checked.
2. Engine Coolant Level Check
Coolant keeps your engine from overheating. It's checked in the expansion tank, not the radiator.
How to check:
Make sure the engine is cold (never check a hot engine)
Locate the coolant expansion tank (usually a translucent plastic tank)
Check the level against the minimum and maximum marks on the tank
The coolant should be between these marks
Never open the radiator cap on a hot engine — pressurised coolant can spray out and cause burns.
3. Brake Fluid Level Check
Brake fluid transfers force from the brake pedal to the wheels. Low fluid can reduce braking effectiveness.
How to check:
Locate the brake fluid reservoir (usually near the back of the engine bay, on the driver's side)
Check the level against the minimum and maximum marks
The fluid should be a clear, light amber colour
If it's dark or murky, it may need changing
Consistently low brake fluid can indicate worn brake pads or a leak in the system — get it checked by a mechanic.
4. Power Steering Fluid Check
Power steering fluid makes it easier to turn the steering wheel. Low fluid can make steering heavy.
How to check:
Locate the power steering fluid reservoir (check your handbook for the exact location)
Check the level against the minimum and maximum marks
Some cars have a dipstick in the reservoir cap
The fluid should be clean and at the correct level
Not all cars have power steering fluid — electric power steering systems don't have a fluid reservoir. Check your handbook to confirm.
5. Windscreen Washer Fluid
While not technically an engine bay check, washer fluid is topped up under the bonnet.
How to top up:
Locate the washer fluid reservoir (usually has a blue or yellow cap with a windscreen symbol)
Open the cap and pour in windscreen washer fluid
Don't overfill — leave a small gap at the top
6. Engine Air Filter
The air filter keeps dust and debris out of the engine. A clogged filter can reduce performance and fuel economy.
How to check:
Locate the air filter housing (usually a black plastic box near the front of the engine)
Unclip or unscrew the housing lid
Remove the air filter and hold it up to the light
If you can't see light through it, it needs replacing
AI-Diagnostics-Pro provides AI-generated information for educational purposes only. Always consult your vehicle handbook and a qualified mechanic for maintenance advice. Content reviewed July 2026.