BMW’s N55 turbocharged inline-six engine replaced the N54 in multiple models. We review the N55’s performance and reliability.
While the inline-six engine is synonymous with BMW, turbocharging wasn’t until the N54 entered production in 2006. Three years later, BMW came out with the N55 as a replacement in 2009.
Unlike the N54, the N55 has a single turbo, but still produces the same power and torque while being more efficient. They share displacement, bore, and stroke, along with the same 10.2:1 compression ratio.
However, two big changes did occur. The first change was the Valvetronic system. “Both the N54 and N55 use BMW’s VANOS system on both the intake and exhaust camshafts, but only the N55 uses the Valvetronic system which allows for variable lift control”, explains Dust Runners Automotive Journal, which provides some substantial background on the system.
The second change was to the fuel injectors, which were switched to a lower-pressure, less expensive Bosch setup. Going to a single, twin-scroll turbocharger offers many advantages, including being easier to package, cheaper to make, more efficient, and more reliable than a twin-turbo setup. Still, the N55 makes 20 more horses than the N54 did, with better fuel economy.
Why an I-6 layout? “The best configuration for a turbocharged engine, the automaker argues, is to have the intake on one side of the engine and the exhaust manifold and turbocharger on the other,” explains Wards Auto. “A ‘V’ engine, by contrast, needs to pump air to both rows of cylinders, which is a more complex arrangement and needs more packaging space.”
What BMWs Have the N55 Engine?
The “35i” badge after the model name denotes the use of the N55, as oppose to a “28i,” which means it’s powered by a four-cylinder engine. Outliers include the 6 Series and 7 Series, which use the “40i” designation, and the BMW M2, which used the N55 until it was refreshed with the S55 M engine.
- 2009-2017: 535i
- 2010-2013: 335i
- 2010-2013: 135i
- 2010-2017: X3 xDrive35i
- 2011-2013: X5 xDrive 35i
- 2011-2015: 335i
- 2011-2014: X6 xDrive 35i
- 2012-2015: X1 xDrive35i
- 2013-2016: 435i
- 2014-2018: X5 xDrive 35i
- 2014-2019: X6 xDrive35i
- 2014-2016: X4 xDrive 35i
- 2013-2016: M235i
- 2012-2015: 740i/Li
- 2011-2018: 640i
- 2016-2018: BMW M2
The N55 Driving Experience
As you would expect from a longtime and multiple Ward’s “10 Best Engines” award winner, the N55 delivers smooth throttle response; excellent power and torque; and a sound many describe as the perfect inline-six.
“We loved the 2012 BMW 335i’s engine, which helped propel the four-door to a 4.8-second 0-60 mph time — far better than the Mercedes C350 and Cadillac ATS with which it was competing,” explains Motor Trend.
Car & Driver was a fan of the N55 in that was in a 2014 BMW X5 that the editors tested. “The boosted 3.0-liter in the 35i is a sweetheart,” said Car and Driver. “It’s smooth and quiet, with a torque curve that looks like the profile of the old airport mesa in St. George, Utah—long, high, and flat, with all 300 lb.-ft. online from 1,300 rpm, barely off idle, to 5,000.”
N55 Engine: Performance and Reliability
There are some common issues for the N55 engine that can affect your BMW, especially as models using it continue to age.
Valve Cover Gaskets and Valve Covers
The rubber valve cover gasket can degrade over time, causing oil leaks. The valve covers themselves can also crack, as the BMW enthusiast site BMW Tuning reports: “The valve cover is made of plastic and the high temperatures cause it to potentially develop cracks down the road. This is a less common issue than the valve cover gasket, and it will typically last closer to 100,000 miles.”
Water Pump
A water pump circulates coolant through the engine block, and the one in the N55 can fail quite suddenly. This failure can occur more frequently on higher mileage cars, usually past 80,000. Signs to look for include leaking coolant, steaming radiator, and the engine overheating.
Oil Filter Housing Gasket
Back to gaskets. The one used in the oil filter housing can fail, causing oil to leak around the filter. While not a problem that requires immediate repair, it will likely need attention at some point, least it drip onto drive belts and cause them to wear prematurely.
VANOS Solenoid Failure
The VANOS system is responsible for variable intake timing on the N55, and over time, the solenoids can fail. It’s also possible for them to become dirty, making them fail prematurely. N55s produced from 2010-2012 had a recall for VANOS bolts. So, be sure to check that this was completed if you’re looking at a BMW from those years.
BMW’s N55 Engine: Vehicle History Owner Experience
Vehicle History always presents an unbiased opinion, and on occasion, we’ll ask our writers to share personal ownership experiences regarding models and engines that we are covering. The author of this article, Machines with Souls‘ Mike D’Ambrosio, is a BMW owner and expert with vast experience with the vehicles and the N55 engine.
“I purchased a CPO 335i in October of 2018,” says D’Ambrosio. “The N55 in the 335 is an excellent motor, and very smooth. However, there were some reliability issues over the course of 45,000 miles.
“I’ve had to replace the valve cover gasket, an oil filter housing, oil pan gasket, front pinion seal, oil filter cover, drive pulley, and drive belt,” he adds. “If you’ve found a BMW with an N55 that you love, consider a pre-purchase inspection to ensure all the seals and gaskets are in good working order.”
Is the N55 Engine Still Relevant?
In 2016, BMW began phasing in the B58 engine, a large improvement over the N55 that featured more power and better efficiency.
However, the N55 is a flexible engine that’s still plenty powerful (BMW offers factory-backed tuning upgrades for more power). It’s also very reliable as long as proper maintenance is completed. One stab of the gas is usually enough to provoke a wide grin, and that makes the N55 an overall excellent engine.
Photos: BMW; Machines with Souls
