As long as this was a new engine and not a second hand engine, the fact that it has had a replacement engine is good news not bad news. Delays the point at which you would need to replace the timing belt, etc. But if the engine is a second hand replacement engine you can reject the car outright because the dealer was under a legal obligation under the 2008 CPRs to disclose that to you. Law here: www.honestjohn.co.uk/faq/consumer-rights/ The Consumer Protection from Unfair Trading Regulations May 2008 (CPRs) contains a general prohibition against unfair commercial practices and, in particular prohibitions against misleading actions, misleading omissions and aggressive commercial practices. The Regulations are enforceable through the civil and criminal courts. This creates an offence of misleading omissions which would not previously have been an offence if the consumer had not asked the right questions. So if a salesman knows a car has, for example, been badly damaged and repaired and does not tell the customer, he could later be held liable if the customer subsequently discovered that the car had been damaged and repaired.