#UnderTheBonnet: Buying a Used Car

What to check before making a purchase

Checking under the bonnet of a used car

Checking Documents


A V5C or log book is a small booklet that tells you who the registered keeper of the vehicle is. It doesn’t need to be present when you buy the vehicle but if it’s not it makes it difficult as you’ll have to request one from the DVLA by application form at your local Post Office. It’s also not a good sign and it would be advisable to check the vehicle details online to ensure it’s not stolen.

Can the owner show you the car’s V5C document that shows they’re the registered owner? If not, ask them why not? You’ll need this document to tax the car and transfer ownership to you.

V5C document for a used car

Check that the VIN (vehicle identification number), engine number and colour matches the information on the V5C. Check that the VIN etched onto the windows and/or lights also match the V5C and haven’t been scratched off.

Valid MOT Certificates

Check that the car has an MOT certificate that’s in date. If it doesn’t it cannot be driven, even for a test drive.

By law all vehicles need to have a valid MOT in order to be insured. If your vehicle is not insured or without a valid MOT it cannot legally be on the road. All MOTs are based on the vehicle, not the owner, so any MOT on the car when you buy it will be valid until it runs out. MOTs are needed yearly in order to keep the vehicle working to its best condition.

MOT certificate for a used car

If the MOT certificate has advisory actions (for example, new tyres) then check if they have been completed – ask the dealer and make sure you see evidence of their completion. Any work that has been done should have a valid receipt as proof and if you don’t see evidence that it’s been done (and it hasn’t) then you may be liable to the work before your next MOT.

Check if the MOT is valid at: https://www.gov.uk/check-mot-status

Service Book

Getting a car serviced is not a legal requirement but it’s always going to go in favour of the vehicle if it has had them. A regular service (every 12k miles or every year) will ensure likely issues are spotted and fixed before it becomes a bigger issue. Always ask for proof of the service and receipts of any work that’s been done.

You can check all vehicle details at: https://www.vehicleenquiry.service.gov.uk/


Having proof of work that’s been done means you’re able to see if there have been previous issues or anything that’s likely to go wrong. It also shows you things that you may not need to work about, for example, new brake pads or a recent oil change.

Checking for Damage

Some used cars have a degree of damage but remember, you are buying a used car so it won’t be perfect. That doesn’t mean you should accept large amounts of damage or wear and tear so check the car thoroughly for damage, including:

  • Any signs of gaps between panels, or mismatched colours. These could indicate poor quality or extensive repairs.
  • Are there any traces of paint spray across the car? This could be a sign of DIY repairs that are designed to cover further damage.
  • Check inside the bonnet to look for evidence of any unusual looking welding. This could indicate that some of the original car parts have been removed and replaced for others.
  • Also check that the tyres are worn evenly and within the legal limit (1.6mm). If they’re worn unevenly, it could be a sign of bad alignment, which could be expensive to fix.

Finally, check for any signs of forced entry or damaged locks which could show they’ve been replaced.

Starting the Car

Warning Lights

We could go into all the different warning lights that can appear but we don’t want to bore you. The message here is that, if there is one, check it out and find out if it’s important. It’s advised that you don’t buy a car with any warning light as it could be the sign of bigger issues later on.


When you start the engine from cold, it shouldn’t make any abnormal noises. Ensure that the car’s radio is turned off so you can hear the noise of the engine when you start it up.


There should also be no signs of excessive visible exhaust emissions.

If you spot white water vapour when the engine is cold, then there’s no need to worry; that’s completely normal. However, blue smoke isn’t: that’s burning oil. Black smoke indicates a serious issue.

Exhaust emissions of a used car

The car should have an emissions test (usually part of its MOT certificate) which will confirm that the car conforms to emissions standards.

Under the Bonnet

When looking under the bonnet, you should look to see whether it has recently been power-washed. If it has, then this could be a sign that the owner is trying to hide evidence of fluid leaks. However, it could also be a sign that they’ve looked after the car well. To decide, look again after a lengthy test drive and take a careful look for spills. Any problems should be clear.

Checking the engine of a used car

Take a look at the underside of the oil cap, too. If there’s a build-up of sludge under it, then it could mean that the car either hasn’t been serviced correctly, or that it usually only drives on short journeys.

Carefully inspect the hoses and belts - these should never have cracks and radiator hoses should not be soft.

Inspect the engine for leaks and corrosion, do this by looking on the block itself, look for oil stains and check the brake fluid reservoir to ensure that it isn’t leaking.

Under the bonnet

Check the oil level in the vehicle. If the oil level is low, then it could be a sign that the vehicle has been neglected. If it’s too high, the car could be using oil quickly or incorrectly.

Test Drive

This is probably the most important thing you should do before buying a vehicle. A test drive means you can feel how the vehicle drives, if there are any questionable noises (don’t have the radio on so you can hear everything), if you like the feel of it and generally if it’s the right car for you. Press all the buttons in the vehicle and we mean everything. Check the sunroof works, the seats move back, forward, up or down as they should, the windows come down, the central locking woks, etc. Check anything and everything that you will use if you buy the car.

Buying a used car can seem daunting but hopefully we’ve helped give you a starting point so you know what you’re looking for.

If you think we’ve missed anything get in touch on Facebook or Twitter.

Images courtesy of iStock.

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