The N46 is documented to suffer from upper timing chain guide splitting and timing chain stretch. Honest John specifically flags split upper timing chain guides on the N46 1,995cc petrol engine. Left unaddressed, catastrophic engine failure is possible.
Rattling or knocking noise on cold start
Timing-related fault codes
Mechanic inspection revealing slack in chain
Engine running rough at idle
DIY: Expert
Valve Stem Seal & Oil Consumption€800-2,500 · 100,000-200,000 kmHIGH
N46 engines are known for hardened valve stem seals leading to oil burning and blue smoke, particularly after cold starts or extended idling. Forum data confirms this is a widespread issue with an established repair cottage industry.
Valve cover gasket leaks are commonly reported on the N46, with forum threads specifically referencing the E90 N46 320i. Oil can seep onto hot engine components and create burning smells or fire risk if neglected.
Forum data documents sporadic low oil pressure at idle on the N46B20, sometimes linked to a faulty oil pressure sensor or switch, but also to genuine internal wear. Head gasket failure between cylinders 3 and 4 has also been associated with oil pressure issues on this engine.
Oil pressure warning light flickering at idle
Low oil pressure reading for 2-3 seconds on startup
Faulty or incorrectly wired lambda sensors are reported on N46 engines, with forum evidence of wiring harness interference causing sensor misreadings. Multiple pre-cat sensors can complicate diagnosis.
Forum data documents N46 engines developing crankcase overpressure, noted by excessive pressure when removing the oil cap. Associated with vibration but reportedly no smoke in some cases. Likely linked to PCV/breather system blockage or wear.
Visible pressure blast when removing oil cap
Whole-car vibration
Oil leaks from multiple seals due to pressure
DIY: Low
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Buying Checklist
Cold-start the engine and listen carefully for any chain rattle or knocking in the first 10-30 seconds — walk away if heard
Request full service history showing oil changes no longer than every 10,000 km; reject any car with Longlife 30,000 km intervals
Perform or request an OBD scan using INPA or ISTA for live lambda data, timing faults, and valvetronic fault codes
Inspect the top of the engine and valve cover area visually for oil seepage or burnt oil residue indicating gasket leaks
Check the oil cap for excessive crankcase pressure (strong blow when removed) and inspect the dipstick for milky oil indicating head gasket issues
Verify the Takata airbag recall has been completed — check with BMW using the VIN before purchase
The BMW N46 320i is a driver's car at heart but carries real mechanical risk, particularly around the timing chain and valve stem seals, both of which can become expensive if ignored. Only buy a well-documented example with consistent short-interval oil change history and no cold-start rattles whatsoever. Budget €1,500–3,000 upfront for preventative timing chain work if the car has no proof of prior replacement above 100,000 km. This engine rewards attentive ownership but will punish neglect quickly and expensively.
Parts People Buy
BMW N46 Timing Chain Kit (chain, guides, tensioner)Link unavailable
BMW N46 Valve Cover Gasket SetLink unavailable
BMW N46 Valve Stem Seal SetLink unavailable
BMW N46 Oil Pressure Sensor / SwitchLink unavailable
BMW N46 Lambda / O2 Sensor (pre-cat)Link unavailable
BMW N46 PCV Crankcase Breather ValveLink unavailable
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