Engine problems are the nightmare scenario for any used car buyer. Repairs can cost thousands – often more than the car is worth. If your engine has developed problems after purchase, here's what you need to know about your rights.
Common Engine Problems
Engine knocking or rattling usually indicates serious internal problems – worn big end bearings, piston slap from worn cylinders, timing chain wear, oil starvation damage, or detonation. Knocking often means the engine is near end of life, with repairs typically requiring an engine rebuild or complete replacement.
Misfiring means the engine runs rough, hesitates, or feels down on power. Causes range from relatively cheap fixes like faulty spark plugs or coils (£100-£300) through to fuel injector problems, compression loss, and major internal damage (£3,000+). A diagnostic scan will usually identify which cylinders are misfiring and why.
Excessive oil consumption – using more than about 1 litre per 1,000 miles – is a fault for most cars. The usual causes are worn piston rings, worn valve stem seals, turbo failure, or internal leaks. Dealers sometimes try to dismiss this as normal, but it's not – it indicates components that were worn before you bought the car.
Exhaust smoke tells you a lot about what's going wrong. Blue smoke means the engine is burning oil (worn rings, valve seals, or turbo failure). White smoke – particularly thick, sweet-smelling steam – indicates coolant is burning, pointing to a head gasket failure or cracked cylinder head. Black smoke means the engine is running rich due to a fuelling problem or sensor fault.
Loss of power can result from turbo failure, a blocked DPF or catalytic converter, fuel system problems, compression loss, or sensor faults. An engine warning light covers many possible faults and always needs investigation – it's never safe to ignore, regardless of what the dealer claims.
Timing chain or belt failure is catastrophic on interference engines – the pistons hit the valves and the engine is usually destroyed. Warning signs include a rattling noise on startup (for chains), no service record of belt replacement, and high mileage without a change. Turbo failure produces loss of power, excessive smoke, a whining noise, oil in the intercooler, and boost leaks – see our turbo failure guide for more detail.
Is It a Fault?
An engine warning light, knocking or rattling, major oil consumption, constant smoking, complete engine failure, and misfiring are all unambiguously faults – there's no reasonable argument that any of these represent a "satisfactory" car.
The timing test matters. Engine problems don't develop overnight. If issues appear within weeks of purchase, the fault was developing at sale, symptoms may have been deliberately masked, and you haven't had the car long enough to cause the wear yourself. Within 6 months, the law presumes the fault was present at purchase – the dealer must prove otherwise.
Watch for signs the dealer knew. A suspiciously recent oil change with cheap oil may be hiding consumption. Additive bottles visible in the engine bay suggest they've been masking problems. Thick oil is a classic trick for quietening engine knocks. An engine bay cleaned spotless could be hiding leaks. And if the dealer insists you view the car with a warm engine, they may be concealing cold-start problems like rattling timing chains or excessive smoke on startup.
Think you might have a claim?
Check if you're entitled to a refund under the Consumer Rights Act. Free, takes 2 minutes.
Your Legal Rights
Consumer Rights Act 2015
A car with engine problems isn't of satisfactory quality (the engine must work), isn't fit for purpose (it must function as transport), and isn't as described (unless the faults were disclosed and priced accordingly).
30-Day Right to Reject
Within 30 days, you can reject for a full refund. Engine faults make this clear-cut – you don't have to accept a repair. If your engine failed on the way home from the dealer, that's the strongest possible rejection case.
After 30 Days
You can request repair, but with major engine problems be cautious: repairs may be temporary, underlying damage may emerge later, and if the repair fails you can reject for a refund with a possible small deduction for use.
When the Engine Is Destroyed
If the engine has failed completely, the car clearly isn't satisfactory quality. Demand a full refund – don't accept a partial repair to a dead engine or a "reconditioned" unit of uncertain quality. Reject outright.
Repair Costs
| Problem | Typical Cost |
|---|---|
| Spark plugs/coils | £100-£400 |
| Fuel injectors | £300-£800 |
| Timing belt/chain | £400-£1,200 |
| Turbo replacement | £800-£2,500 |
| Head gasket | £600-£1,800 |
| Engine rebuild | £2,000-£5,000 |
| Engine replacement | £2,500-£8,000+ |
Engine repairs are the most expensive you'll face. Don't pay if the fault existed at sale.
Evidence You'll Need
Document the symptoms with video of any knocking or rattling, records of smoke colour and when it occurs (cold start, under load, etc.), a log of oil consumption rate, photos of warning lights, and detailed descriptions of performance issues.
Get a professional diagnosis from an independent garage – not one connected to the dealer. Ask for a compression test, oil analysis if appropriate, a diagnostic scan for fault codes, a visual inspection, and a written report covering their findings and whether the wear is consistent with the car's age and mileage.
Check the car's history through service records (look for oil changes, timing work, and any evidence of prior engine problems), MOT history (emissions failures, smoke advisories), any previous owner complaints, and relevant manufacturer recall information.
Common Dealer Excuses
"Engines wear out"
Your response:
"Not within [X] weeks of purchase. This engine was already failing when you sold the car."
"It's a high-mileage car"
Your response:
"High mileage doesn't excuse selling a car with a failing engine. You're still required to sell goods of satisfactory quality."
"You should have spotted it on the test drive"
Your response:
"The duty is on you to sell satisfactory goods, not on me to be a mechanic. Many engine faults aren't obvious without diagnosis."
"The warning light might be nothing"
Your response:
"The warning light indicates the car's own systems have detected a fault. 'Might be nothing' isn't acceptable – diagnose it properly."
"We'll top up the oil for you"
Your response:
"Topping up oil masks excessive consumption. The underlying fault still exists and needs proper repair."
"It just needs a service"
Your response:
"[Knocking/smoking/misfiring] isn't solved by a service. This is a mechanical fault."
What to Do
Don't make it worse. If you suspect serious engine problems – low oil pressure, overheating, severe knocking – stop driving immediately. Continued driving with these symptoms causes rapid, irreversible damage, and the dealer could argue you made the problem worse. Arrange recovery if needed, and document why you stopped.
Get a proper diagnosis from an independent specialist. A full engine assessment including fault code reading, compression test, and a written report gives you the evidence you need. Then check the car's history – MOT records for emissions failures or smoke, service records for prior engine work, and whether the engine has been replaced before.
Write to the dealer formally stating the specific fault identified, when symptoms started, your mileage since purchase, a clear demand (rejection or repair), and a 14-day deadline for response. Keep records of everything.
Make a decision based on severity. For a minor fault, you might accept a repair with a written guarantee. For a major fault, consider rejection. For complete engine failure, reject outright – don't accept a reconditioned unit of unknown provenance.
Escalate if the dealer refuses. Your finance company is jointly liable and often more cooperative than the dealer. Trading Standards can investigate the dealer's practices. And small claims court is accessible, affordable, and effective for claims under £10,000.
Recommended reading
Special Cases
Timing belt/chain not done: If the belt was due for replacement and the dealer didn't do it or disclose it, the car wasn't of satisfactory quality. If it subsequently fails and destroys the engine, they're liable for the full cost – not just the belt replacement they should have done.
Previous engine replacement: If the engine was previously replaced, was this disclosed? Why was it replaced? Non-disclosure of a replacement engine may constitute misrepresentation, and the replacement engine's history and quality become relevant.
Known model faults: Some engines have well-documented problems – excessive oil consumption on certain BMW and VAG engines, timing chain issues on various makes, and the Ford EcoBoost wet belt failure that can destroy the engine. Research your specific engine, as known issues don't excuse the dealer selling you a faulty car, but they do help prove the problem isn't something you caused. Technical Service Bulletins from the manufacturer may exist that support your case.
Remapped or modified engines: If the engine was remapped and this wasn't disclosed, the car isn't as described. Remaps can cause accelerated wear and component failure, and the warranty may be voided. This is a clear misrepresentation if you weren't told.
The Bottom Line
Engine problems are catastrophic for used car buyers. A failing engine can turn a £5,000 car into a £500 one overnight. But you have rights: an engine that doesn't work properly isn't satisfactory quality, problems appearing shortly after purchase were pre-existing, and you're entitled to rejection or repair at the dealer's expense. Don't accept excuses about "wear and tear" or "high mileage" – you're entitled to a car that actually runs properly.
Engine problems on your recently purchased car? Check if you qualify for a rejection before it gets worse.
Engine problems on your recently purchased car? Check if you qualify for a rejection before it gets worse.
Related Topics
