BMW 5 Series 523i.
What to Check Before Buying.

The BMW 5 Series 523i suits buyers wanting executive comfort and performance without the running costs of six-cylinder models. This 2.5-litre petrol inline-six variant, produced between 1995 and 2000 for the E39 generation and 2007 to 2010 for the E60, delivers a strong balance of smoothness and efficiency. The engine is generally reliable when properly maintained, though E60 models can suffer from electric water pump failures and occasional issues with the variable valve timing system. When inspecting a used 523i, check the service history thoroughly for evidence of regular oil changes, as these engines are sensitive to poor maintenance. Examine the cooling system carefully, particularly the water pump and expansion tank on later models. Listen for any unusual rattles from the valve train during a cold start. Check all electrical systems work correctly, especially on the E60 where iDrive and comfort features can be expensive to repair. A comprehensive inspection before purchase will help identify potential issues early.

The average used car has 3+ known model faults the seller won't mention.