Most 2021 i30 diesels use Hyundai’s 1.6 CRDi engine with a 6-speed manual — reasonable power (about 115–136 hp depending on tune) and very good real-world mpg on longer trips. These engines have DPF and EGR systems and some late diesels also use AdBlue/SCR, so they prefer regular motorway runs rather than lots of short-town trips; the manual clutch is the main wear item to watch on this drivetrain.

• DPF behaviour and regeneration history — ask for evidence of regular long runs or recent forced regens; check for frequent warning lights or limp-mode events.
• If fitted, check AdBlue tank level, dosing pump operation and any injector leaks or warning messages.
• Clutch feel and bite (slipping, judder or heavy pedal) and look for clutch replacement receipts or recent mileage consistent with clutch life.
• Turbo and boost health — listen for whistle/whine, check for blue/grey smoke on acceleration and test for lag across the rev range.
• Underside and wheel-arch corrosion around seams and exhaust hangers (Irish salty roads accelerate local rust after 4–6 years).