The facelift is the key buying split because most Cooper S models move to the improved N18 engine, which is notably less troublesome than the earlier N14.
The "Death Rattle" is the defining issue of the N14-engined Cooper S and JCW. The chain stretches and the tensioner fails, often due to low oil levels, leading to valves hitting pistons if ignored.
Prince engines (N14/N18) can consume up to 1 litre of oil every 1,000 miles. Neglecting this leads to timing chain failure and turbo damage. Many owners fail to check the dipstick regularly enough.
HPFP failure causes long cranking, stumbling under load, and limp mode on turbo petrol cars, particularly where heat and infrequent fuel-filter maintenance have taken a toll.
The FRM controls lights and windows. It is prone to failing if the battery is disconnected or goes flat, or due to water ingress from blocked sunroof drains.
The plastic thermostat housing and attached pipework crack, causing slow coolant loss that often gets ignored until the engine overheats.
Direct-injection N14 and N18 turbo cars build carbon on the intake valves, costing power and making idle quality feel rough. "Walnut blasting" is the standard UK fix.