The N55 is widely considered to be one of the best tunable engines from German automaker BMW. BMW built this engine from 2009 to 2019 and used the motor in the majority of the BMW product lines, including the 3 Series, 4 Series, and 5 Series sedans.
That said, is the N55 engine reliable? In this article, we’ll take a look at the N55 engine and discuss some of the engine’s reliability issues.
Table of Contents
BMW N55 engine overview
5 most common issues with the BMW N55 engine
1. Valve cover and oil filter housing gasket leaks
2. Turbocharger wastegate rattle
3. Electric water pump failure
4. High-pressure fuel pump (HPFP) issues
5. Charge pipe cracking
Conclusion
BMW N55 engine overview
The BMW N55 is a turbocharged inline-six-cylinder engine that combines performance, economy, and cutting-edge technology. The N55, launched in 2009 as the successor to the N54, is BMW’s first production engine to have a single twin-scroll turbocharger.
The design maximizes turbo performance, minimizing lag and producing improved power throughout the rev range. Additionally, the N55 also uses BMW’s Valvetronic valve timing, double-VANOS cam timing, and direct fuel injection for performance and fuel efficiency.
The N55 engine is considered to be versatile and has appeared in a number of BMW models, including the F30 335i and F32 435i sedans, the E90/E92 335i coupes, and the F10 535i luxury car, displaying its adaptability to various types of vehicles and driving style.
It also powers compact sports coupes such as the X3 xDrive35i, X4 xDrive35i, and X5 xDrive35i. The high-performance crowd, meanwhile, will find the turbocharged engine in the M135i, M235i, and even the first-generation M2, beloved by car enthusiasts.
5 most common issues with the BMW N55 engine
Even though it’s been deemed more reliable than its predecessor, there are a few flaws with the BMW N55 engine that drivers should be aware of. Below, we’ll detail five of the most frequent problems:
1. Valve cover and oil filter housing gasket leaks
The valve cover gasket and oil filter housing gasket are among the most common maintenance problems when it comes to the BMW N55 engine. These gaskets are used to seal various components and prevent oil from seeping into the areas where it can damage the engine. But, given the engine’s high operating temperatures and pressures, these gaskets are prone to wear down over time.
The valve cover gasket sits between the valve cover and the cylinder head, securing the top of the engine. With time, the gasket is likely to weaken and crack, leaking oil. Signs that a valve cover gasket is leaking include the smell of burning oil, oil seeping onto the hot exhaust manifold, visible oil at the valve cover corners, or oil on the engine itself. Unrepaired, the leak can create additional problems, including misfires or damage to surrounding parts, such as ignition coils.
The issue also affects the oil filter housing gasket, which seals the oil filter housing and the block. When this gasket breaks, oil is likely to enter parts such as the alternator or belt. This can lead to electrical issues or accessory drive problems.
Leaks here are commonly recognized by oil staining on the filter housing and gradual oil loss and must be repaired to keep the engine running. The valve cover gasket and oil filter housing gasket are pretty easy to replace, though it will require cleaning the mating surfaces to get a good seal with the new gasket.
2. Turbocharger wastegate rattle
A rattle emanating from the turbocharger wastegate is one of the more common problems with the BMW N55 engine, which is powered by a single twin-scroll turbo for both performance and efficiency.
The wastegate, which sends exhaust to the turbocharger, can eventually wear down, resulting in a metallic rattle. It’s usually most evident while idling or at low RPMs, when the turbo is not working hard.
Wastegate rattle is generally caused by a loose wastegate actuator or linkage. The actuator positions the wastegate flap, and as tolerances reduce with age or use, the flap will begin to vibrate. In extreme cases, such wear can cause leaks in the wastegate and loss of boost pressure. This results in poor engine performance, sluggish acceleration, and worse fuel economy.
Unfixed, a damaged wastegate can further stress the turbocharger and other engine parts, resulting in higher repairs. For retailers and repair professionals, early detection is key. Occasionally, the problem can be temporarily solved by tuning the actuator, but more frequently, the turbocharger system or wastegate must be replaced.
3. Electric water pump failure
The N55 incorporates an electric water pump for superior cooling efficiency and accuracy. But this part can wear out after 60,000 to 80,000 miles and can leave drivers stranded on the roadside if ignored.
Engine overheating, dashboard warning lights, sputtering coolant, and poor cooling system performance are all signs of a leaking water pump. Drivers may even experience strange sounds coming from the engine bay or sudden power cuts caused by thermal management.
As the water pump is a critical component in keeping the engine running, diagnosis and replacement of this issue are imperative.
4. High-pressure fuel pump (HPFP) issues
Problems with the BMW N55 engine’s high-pressure fuel pump (HPFP), which supplies fuel at the high pressures needed by the engine’s direct injection system, are also well-documented.
When the HPFP falters, it can interfere with the accuracy of the fuel’s flow, affecting performance. Typical signs of a broken HPFP include trouble starting, prolonged cranking, noisy idling, stalling, activation of limp mode, and a noticeable loss of power during acceleration.
While BMW has made significant changes to address these concerns through improvements in pump technology and production, it can still fail, particularly in older models. Fuel contamination, internal component wear and tear, or faulty fuel system electronics can all lead to HPFP failure.
Fixing a damaged HPFP is not a simple, cheap fix, so diagnostic and prevention measures are important. Mechanics can employ powerful diagnostics to detect early HPFP faults, such as error codes (e.g., P142E or P0087) or incorrect fuel pressure readings.
5. Charge pipe cracking
The BMW N55 plastic charge pipe runs from the intercooler to the intake manifold, but it can crack when exposed to high temperatures and pressure around the turbocharger. That will eventually result in the part warping and eventually cracking, leading to boost leaks, which means decreased power, poor throttle response, and even misfires.
It’s a good idea to replace the plastic charge pipe with a strong aftermarket aluminum or silicone component. They are resistant to heat and more durable, less prone to cracks, and maximize air circulation. Additionally, performance charge pipes should work, which increases airflow, keeping the engine efficient and giving owners reliable operation.
Conclusion
The BMW N55 engine has a powerful combination of efficiency and performance but is not without its share of issues. Oil leaks, electric water pump failures, HPFP failures, charge pipe cracks, and turbocharger wastegate rattle are just a few of the problems that impact reliability and require special care.
To address these problems, businesses should ensure that they stock the right auto parts so that customers can find the necessary parts to get their BMW engine back up and running.
