Looking at a used car is a situation where it's easy to get carried away. The car looks nice, the seller talks convincingly, the price seems fair. And then, three weeks later, the engine starts knocking or the coolant disappears without a trace. You can predict most expensive surprises if you know what to look for while you're still at the seller's place.
What to Check While the Engine Is Cold
The most important rule: show up for the viewing while the car is cold. If the engine is warm when you arrive, the seller started it before you got there — and that might mean they wanted to hide cold-start problems.
Open the oil filler cap and look at the underside. If you see yellowish foam or emulsion, that's a sign that coolant is mixing with the oil. The most common cause is a blown head gasket, and that's an expensive repair. A greasy, thick sludge on the cap points to infrequent oil changes or a faulty PCV valve.
Check the coolant expansion tank. The fluid should be clean and the right colour (green, pink, or orange depending on the type). If you see an oily film on the surface or dark particles floating around, it may mean the head gasket is leaking and combustion gases are forcing their way into the cooling system.
Check the engine oil level on the dipstick. The oil should sit between the MIN and MAX marks. If it's well below minimum, the car either burns oil or the owner hasn't been keeping up with maintenance. Pay attention to the colour as well: black oil isn't automatically bad, but if it's overly thick and gritty, that speaks to neglected oil changes.
What to Listen and Watch for When You Start the Engine
Stand next to the exhaust while someone else starts the engine. White smoke that clears within the first minute or two is normal condensation, especially in cold weather. But white smoke that doesn't stop, smells sweet, and gets worse with revs almost certainly means coolant is entering the cylinder.
Blue smoke on startup points to worn valve stem seals or worn piston rings. The engine is burning oil, and that's a problem that only gets worse over time. Black smoke on a petrol engine means an overly rich mixture, usually caused by a faulty sensor or a fuel injection issue.
Listen to the engine while it's running cold. A brief knocking sound in the first 5–10 seconds can be normal, especially on engines with hydraulic lash adjusters (HLA). The oil needs time to fill the channels. But if the knocking lasts longer than 15–20 seconds or is particularly loud, it could be a worn timing chain, crankshaft bearings, or a more serious problem in the bottom end.
Pay attention to the idle as well. The engine should run smoothly, without jerking and without fluctuating RPMs. If the tachometer needle bounces up and down or the car shakes slightly while standing still, something is off — whether it's the spark plugs, ignition coils, intake flaps, or a vacuum leak.
The Test Drive — What to Watch For
The test drive should last at least 15 minutes — long enough for the engine to reach operating temperature and for problems that don't show up when cold to surface.
Run the gearbox through all gears. A manual transmission shouldn't grind when shifting, and the clutch shouldn't slip under hard acceleration in a higher gear. With an automatic gearbox, watch for jerks when shifting, delays, or unusual sounds.
Test the brakes on a quiet stretch of road. The car must brake in a straight line without pulling to one side. If you feel vibrations in the steering wheel or brake pedal, the discs are most likely warped. Squealing under light braking usually means the pads are worn.
Let off the throttle on a flat road and listen. Noise that appears when you release the gas but disappears when you press it again often comes from worn CV joints or wheel bearings. Testing with left-right turns in a parking lot can reveal the characteristic clicking of a worn CV joint.
Turn on the air conditioning and check that it actually cools. A non-working or weak A/C might just need a refrigerant recharge, but it could also be a compressor on its last legs — and that's a significantly more expensive fix.
Signs the Odometer Has Been Rolled Back or the Car Has Been Dressed Up
Compare the interior condition with the displayed mileage. A worn steering wheel, scuffed pedals, a sagging driver's seat, and a peeling gear knob on a car supposedly showing 120,000 km clearly tell you it's done considerably more.
Look at the screws on the instrument panel and around the steering column. If they're damaged or show tool marks, someone may have taken the dashboard apart to access the odometer. On newer cars the mileage is rolled back via software, but records often remain in other control units that OBD diagnostics can read.
Before putting down a deposit, it pays to check the car's documented history. Using the chassis number, the easiest way is through carVertical, which pulls real odometer readings by date from international registries, along with recorded accidents, number of previous owners, and indicators of theft or total loss. We consider this a mandatory step before buying any used car, and you can use the code GAGA at checkout for a 20% discount.
Also check the service book if one exists. Regular entries with service stamps, parts invoices, and oil change receipts paint a better picture than any promise from the seller.
When to Bring a Mechanic or Take the Car to a Workshop
Everything we've described so far you can do on your own, without any equipment. But it's only a first filter. If the car passes your inspection and you're still interested, the next step is a pre-purchase inspection at an independent workshop.
On a lift, a mechanic sees what you can't: the condition of the undercarriage, sills, leaks from the gearbox and differential, the state of the tie rods, worn joints, and bushings. OBD diagnostics reads stored fault codes across all control units, not just the engine. Sometimes a seller clears the codes before the sale, but certain faults reappear as soon as the car is driven.
Don't take the car to a workshop the seller suggests. Choose an independent shop you trust. An hour on a lift with a diagnostic scanner can save you thousands of marks and months of frustration.
If you're not sure where to get an inspection done, get in touch. It's better to invest an hour now than to spend months paying for repairs you didn't expect.