N55 vs B58: What Changed and Which Engine Is Better?
Image: BMW B58B30C Complete Engine with just 30K Miles for £7,249.99 at MT Auto Parts
For most of the 2010s, a BMW with a 35i badge meant one engine: the N55, a 3.0-litre turbocharged straight-six. From 2015, BMW began replacing it with the B58 engine, and the badges changed to 40i. Both engines are smooth, quick and well liked, but the B58 is a different engine underneath, and the differences matter if you are buying a car or a replacement engine.
N55 vs B58 at a Glance
The BMW N55 Engine
The BMW N55 engine replaced the twin-turbo N54 in 2009, first appearing in the F07 5 Series Gran Turismo. It swapped the N54's two turbochargers for a single twin-scroll unit, added Valvetronic variable valve lift and used solenoid injectors in place of the N54's piezo type. In F-generation cars you will find it in the F20 M135i, F22 M235i, F30 and F31 335i, F32 435i, F10 and F11 535i, F25 X3 and F26 X4 xDrive35i, and the original F87 M2.
N55 engine reliability
The N55 is a big improvement on the N54, which was known for high-pressure fuel pump, injector and wastegate problems. Most N55 faults are well understood and relatively cheap in parts, although labour can quickly add up:
Electric water pump and thermostat. The most common serious fault. Failure can be sudden, and the car will warn of overheating with fault codes such as 2E81. Failures have been reported anywhere from around 30,000 to well over 100,000 miles.
Oil filter housing gasket. Leaks oil onto the auxiliary belt, which can then slip or break. It is worth checking on any high-mileage car.
Valve cover and gasket. The plastic cover and its gasket harden with heat. A burning-oil smell after a run is the usual sign.
VANOS solenoids and early-car issues. Worn or dirty solenoids cause rough running and timing fault codes. Some early cars, built around 2010 to 2011, also had high-pressure fuel pump problems, and in the US BMW recalled 2010–2012 six-cylinder models to replace VANOS housing bolts.
Tuned N55s: The N55 responds very well to remapping, and many have been modified. The plastic charge pipe is a known weak point on tuned cars. Ask about any modifications and check that the car runs cleanly.
The BMW B58 Engine
The B58 arrived in autumn 2015 in the F30 340i and is part of the same modular family as the B48 four-cylinder petrol and the B47 and B57 diesels. It soon spread to the M140i, M240i, 440i, 540i and 740i, and is now the standard six-cylinder petrol across the G-generation range. Toyota also uses it in the GR Supra.
BMW changed a lot. The block is closed deck, which makes it stiffer and better at coping with higher cylinder pressures. The stroke is longer, and the intercooler is a water-to-air unit built into the intake manifold, so the charge air has a much shorter path to the cylinders. The timing chain sits at the rear of the engine. In 2018, BMW updated the engine (often called the B58TU) with higher-pressure fuel injection, a revised one-piece timing chain, separate cooling circuits for the head and block, and a petrol particulate filter.
What is the B58B30C?
B58B30C is the engine code for the updated B58, fitted to many G-generation 40i models from late 2018 onwards. BMW's parts catalogue lists it for cars including the G05 X5, G06 X6 and G07 X7 xDrive40i, the facelifted G11 and G12 740i, the 840i and the G29 Z4 M40i. When you are buying a replacement engine, the full engine code matters more than the badge: an early B58 and a B58B30C are not interchangeable without checking ancillaries, wiring and software.
B58 engine reliability
The B58 has a strong reputation and has so far avoided the serious design faults seen on some earlier BMW engines. It is not fault-free. Coolant leaks from the water pump, expansion tank or pipework are the most reported issue, followed by the familiar valve cover and integrated PCV valve, and oil filter housing leaks at higher mileage. As with any direct-injection petrol engine, carbon can build up on the intake valves over time.
Oil on both engines: Both engines run long service intervals with BMW Longlife oil. Changing the oil more often than the service indicator suggests, especially on cars used for short trips, is the simplest way to protect the turbo, VANOS and timing chain.
N55 vs B58: Which Engine Is Better?
On engineering and track record, the B58 is the better engine. It is stronger, more efficient, more refined and suffers fewer of the cooling and oil leak issues that most N55s will need sorting at some point. It also takes power upgrades well, thanks to its closed-deck block.
The N55 is still a very good engine and much cheaper to buy into. An M135i, 335i or 435i with full history and evidence that the water pump, thermostat and oil filter housing gasket have been done can be excellent value. Budget for those jobs if there is no record of them.
If you are looking for an N55 or B58 engine for sale, match the full engine code to your car, not just the badge, and check the donor vehicle's mileage. MT Auto Parts lists used BMW engines and engine parts with the donor car's recorded mileage and condition notes, and almost all parts carry a 30-day warranty (T&C apply).
FAQ
Is the BMW N55 a reliable engine?
The N55 can be a reliable engine when properly maintained, but common issues include oil leaks from the valve cover and oil filter housing gaskets, electric water pump failure and charge pipe cracks. Check the service history and inspect these areas before buying a used BMW. Read our guide to common BMW N55 engine problems for symptoms and repair advice.
Is the BMW B58 more reliable than the N55?
Generally, the B58 has a stronger reliability reputation than the N55, although both engines need proper maintenance. B58 owners may encounter coolant loss, valve cover leaks, VANOS faults and turbocharger-related issues as mileage increases. Our guide to BMW B58 engine problems after 100,000 miles explains what to look for in higher-mileage examples.
Which BMW models have the N55 engine?
The N55 was fitted to various BMW models, including selected versions of the 1-6 Series, as well as the X1-X6. Applications vary by model year and specification. See our blog post fully explaining the list of BMW models equipped with the N55 engine.
Which BMW models have the B58 engine?
The B58 is found in selected petrol versions of the BMW 2-8 Series, alongside models such as the Z4, X3-X6. It also powers the Toyota GR Supra 3.0. The exact engine variant and power output depend on the model and production year. Read our guide to which BMW models have the B58 engine.
When did BMW replace the N55 with the B58?
BMW introduced the B58 in 2015, initially in the F30-generation 340i. The changeover happened gradually across the range. For example, the M135i and M235i were succeeded by the B58-powered M140i and M240i in 2016. Other models switched at different times, so the engine fitted depends on the exact model and production year.
What are the most common BMW B58 problems after 100,000 miles?
Higher-mileage B58 engines may develop valve cover gasket leaks, coolant loss, water pump problems, VANOS faults or wastegate rattle. These issues are not inevitable, and a car's maintenance history plays an important role in its condition. Read our detailed guide to BMW B58 engine problems at 100,000 miles and beyond.
Can I replace an N55 engine with a B58?
A B58 is not a direct replacement for an N55. Differences in engine electronics, wiring, cooling and supporting systems make a conversion a complex project. For most owners, sourcing a compatible replacement N55 is the more practical option. Always check the VIN and engine specifications before ordering a replacement.
How can I tell whether my BMW has an N55 or B58 engine?
Check the VIN using a BMW parts catalogue or ask a BMW specialist to identify the engine using diagnostic equipment and vehicle records. Badges such as 35i and 40i can provide a clue on some models, but they are not definitive proof. Confirm the exact engine code before buying replacement parts or an engine.
Disclaimer: This article is for general information only. Engine applications, codes and specifications vary by market and model year; always confirm the engine code for a specific vehicle by VIN. Any mileages or costs mentioned are indicative and will vary with maintenance history and workshop. Have faults diagnosed by a qualified BMW specialist before committing to repairs.
