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Engines · BMW

BMW N55 turbo straight-six common problems

The N55 is a 3.0 litre petrol straight-six with a single twin-scroll turbo, direct injection and Valvetronic, built from 2009. It replaced the twin-turbo N54 and was itself replaced by the B58 from 2015, and it powered BMW's 35i models, the M135i, M235i and the original M2. Otherwise a strong engine, and generally more reliable than the N54.

Common problems and what to look for on the N55

The known issues most worth checking when you view a car with this engine. None of them means a car is a bad buy, but they're worth knowing about before you buy, and a good history often shows they've been dealt with.

  1. Electric water pump and thermostat failure

    What to look for: Watch the temperature on the test drive and check for coolant or engine warnings. A cooling fan running at full speed, steam or a smell of hot coolant are warning signs. Ask for an invoice for a replacement water pump and thermostat.

    Why it matters: The N55's electric water pump is a known weak point and tends to stop working rather than leak slowly. Failures have been reported as early as 30,000 to 40,000 miles, though some pumps go well past 100,000. The pump and thermostat are normally replaced together, and a car with that invoice is in a good position.

  2. Oil leaks from the rocker cover, oil filter housing and sump

    What to look for: Use a torch to look around the rocker cover on top of the engine, at the oil filter housing and the drive belt at the front, and under the car at the sump. Look for wet oil, oily grime on the belt, drips on the ground and a burning oil smell after the test drive.

    Why it matters: The gaskets harden with heat cycles, and the plastic rocker cover, which also contains the crankcase breather valve, can crack with age. Oil from the filter housing can reach the drive belt and make it slip or shred. These are well-known jobs for a specialist, and many cars have had them done.

  3. Split charge pipe

    What to look for: On the test drive, accelerate firmly in a middle gear. A sudden loss of power, a whoosh of escaping air or a warning light points to a split charge pipe. Ask whether the pipe has been replaced, and with what.

    Why it matters: The plastic pipe between the intercooler and the throttle body can split and let boost escape. It is most common on remapped cars running extra boost, but standard cars are worth checking too. Owners often fit a stronger aftermarket pipe once the original fails.

More known issues, covered in the full guide for each car

  • High-pressure fuel pump on early engines
  • VANOS solenoid failure
  • Carbon build-up on the inlet valves

Cars with the N55

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General points for the engine, last checked October 2026. Every car is different, so treat this as a guide to what to look at, not a verdict on any car. CrankSight is independent and has no connection with any manufacturer.