BMW sDrive18i
Compact turbo four-cylinder based on the PSA collaboration (Prince engine). Timing chain and turbocharger are known weaknesses; regular oil changes are essential.
Underpowered
Too little engine for too much car. Hills become an exercise in patience.
Engine Weaknesses 7
Prince engine with known timing chain defect. Plastic chain tensioner becomes brittle, chain stretches. If ignored, valve and engine damage is likely.
Symptoms: Rattling on cold start, engine warning light, rough idle, power loss
The O-rings on the turbocharger oil feed and return lines harden and crack. Oil enters the engine bay and, if repair is delayed, can starve the turbocharger of lubrication.
Symptoms: Burning oil smell; visible oil film around the turbocharger; slight blue smoke under acceleration; whistling turbo noise if bearing damage develops
From around 100,000–150,000 km, N13 engines show increased oil consumption through worn piston rings and valve stem seals. Ignored oil consumption causes cylinder wall scoring.
Symptoms: Oil level drops more than 0.5 L/1,000 km; light blue smoke when accelerating; oil pressure warning at low level; no oil spots under the car (oil is being burned)
The plastic coolant connector at the rear of the cylinder head warps from heat and loses its seal. Affects early F20 build dates up to around 2014. Improved replacement part available.
Symptoms: Coolant level warning, dried coolant traces on the gearbox casing, continuous coolant loss without visible overheating.
The turbocharger shaft seals become porous and allow oil into the charge air flow. Occurs especially at high mileage and with frequent short-trip driving.
Symptoms: Blue smoke on cold start or under hard acceleration, increased oil consumption, oil mist in the intercooler, occasional sweet smell from the exhaust.
Wear in the wastegate mechanism causes rattling, especially at low rpm. Less widespread than on the N54 but documented.
Symptoms: Metallic rattling at low load, clattering at idle
The camshaft adjustment solenoid valves in the PSA/BMW Prince engine become fouled and wear. Affordable Pierburg replacement valves are available; fault codes on failure are straightforward to diagnose.
Symptoms: Rough idle, hesitation at low rpm, engine warning light, camshaft adjustment fault code.
Vehicle Weaknesses 7
The transfer case (ATC350) on xDrive variants suffers premature wear of the needle bearing at the propshaft take-off. Noises from around 100,000 km; complete failure is possible.
Steering knuckles, strut mounts, driveshaft flanges and underbody components corrode early. BMW classifies it as surface rust and declines warranty.
Front axle shock absorbers wear out from around 130,000 km. Secondary damage through increased tyre wear and heavier loading of control arms and springs is possible.
The 12V on-board electrics are sensitive to voltage drops. A weak battery can cause simultaneous failure of ABS, DSC, xDrive and the fuel pump. A faulty main relay (K2003a) is also a known single cause.
The electric power steering on early production years can slightly 'notch' when turned. The car then wanders off course at higher speeds. A revised steering rack (PUMA) was fitted from model year 2011/2012.
Wheel bearings — especially at the rear — wear out prematurely on the E84 from as early as 20,000–50,000 km. If both sides fail, they should be replaced simultaneously.
On the N20 petrol engine, the oil filter module and porous coolant hoses can leak — sometimes only visible at operating temperature. In the worst case, coolant enters the engine oil.