While BMW is best known for their smooth naturally aspirated inline sixes, they have a history with 4-cylinder engines as well. Their first big success in the US, the 2002 sport sedan, came with the M10 2.0L 4-cylinder, and the addition of fuel injection turned it into the 2002tii, which you can now find on Bring a Trailer any day of the week selling for more than a new 3-Series sedan. Nelson Piquet won the 1983 Formula 1 championship in a Brabham powered by a BMW M12 4-cylinder, which was “related to” the M10 and made 850hp in qualifying spec – further development led to up to 1400 hp during the 1986 season. The first-ever BMW M3 used a high-revving 4-cylinder instead of the torquey 6-cylinder in the 325i.

When BMW released a new 3 Series for the 2012 model year, the base model replaced a 3.0L 6 cylinder with a 2.0L turbo 4 (engine code N20) while keeping the same name. The new 328i made more power than the previous one, while delivering up to 34 mpg. This engine quickly spread to every other BMW -28i model. BMW also produced a version of this engine for some 328i models that met stricter SULEV emissions standards, which has many of the same performance specs and shares most of the parts but got a new engine code (N26). To check if your 328i has the N20 or N26 engine, you can check the emissions label on the underside of the hood. If the emissions programming is LEV (Low Emissions Vehicle) or ULEV (Ultra Low Emissions Vehicle), your engine code is N20. If it is SULEV (Super Ultra Low Emissions Vehicle) then you have the N26 engine.

While BMW surely learned a lot from the famously problematic N54 twin-turbo 3.0L, the N20 still has a couple of issues. Much like the M62 V8 from the late 90’s 540i and 740i, the timing chain guides are made of plastic that wears prematurely, causing the timing chain to lose tension, and if that problem goes untreated long enough, the engine could lose timing and cause irreparable damage. BMW extended the warranty for the timing chain to 7 years/70k miles to address complaints about this. Oil leaks from the (also plastic) valve cover and oil filter housing are common as well, just like they are on the N54 and N55 6-cylinders.

One N20 issue that is specific to the turbocharger system is a rattle from the wastegate on cold starts. While the noise may sound problematic, it’s actually intentional, to a limited degree. When the metal of the exhaust manifold expands with heat, the slack in the wastegate flapper goes away and the wastegate actuation tightens up. If you continue to get this noise when the engine is at operating temperature, this usually indicates that the bushing inside your exhaust manifold is worn beyond acceptable tolerances. While it is technically possible to repair this problem, replacing the bushing requires removal of the turbo, grinding off welds, pressing the bushing, and re-welding of the flapper arm assembly. Almost all of our customers, even the most experienced technicians, will opt for a complete turbocharger replacement rather than attempt this repair. This issue happens on both the pneumatic and electronic wastegate versions of the N20 turbos. Unfortunately, if the bushing inside the turbine housing is excessively worn, tightening of the wastegate actuator rod, or replacing the actuator with a new unit is a temporary fix, at best.

Despite the fact that it says “Twin Power Turbo” on the engine cover, the N20 only has a single turbo. Twin Power Turbo refers to the twin-scroll turbocharger, where the exhaust manifold is specifically designed to route exhaust pulses timed to the firing order of the engine. This means the turbo can spool up quicker and more efficiently.

The N20 uses a Mitsubishi TD04-LR6 turbo, but there are two distinct variants of it – an earlier model with a pneumatic (vacuum) wastegate actuator, and a later one with an electronic wastegate actuator. For some specific year/make/model combinations, the change happened midway through the model year, so you may need to verify your vehicle’s production date. This is the exact date that your vehicle rolled out of a BMW factory, and you should be able to find it on the VIN label on your driver’s door jamb. You can also contact us with your vehicle’s VIN and we can look that up as well. All vehicles with the N26 engine use the electronic version.

Early Pneumatic Actuator Turbo

New OEM w/ One Year Warranty: New Genuine OEM Mitsubishi Turbocharger For 2012 2013 BMW 320i 328i 528i X1 X3 Z4 2.0L TUR-100028-MTN

Remanufactured OEM w/ Two Year Warranty: Turbochargers Direct Remanufactured OEM Mitsubishi Turbo For BMW 228i 320i 328i 428i 528i X1 X3 X4 X5 Z4 N20 TUR-102737-TDR

New Aftermarket w/ Three Year Warranty: New Factory Turbochargers Replacement Turbo For BMW 320i 328i 528i X1 X3 Z4 2.0L N20 TUR-100028-FTN

Fits:

2012 320i w/ Prod. Date of 10/31/2012 or earlier

2012 328i w/o SULEV Emissions AND w/ Prod. Date of 6/30/2012 or earlier

2012 528i

2013 528i w/ Prod. Date of 6/30/2013 or earlier

2012 X1 sDrive28i & xDrive28i w/ Prod. Date of 6/30/2012 or earlier

2013 X3 sDrive28i & xDrive28i w/ Prod. Date of 3/31/2013 or earlier

2012 Z4 sDrive28i

2013 Z4 sDrive28i w/ Prod. Date of 8/31/2013 or earlier

Later Electronic Actuator Turbo

New OEM w/ One Year Warranty: New Genuine OEM Mitsubishi Turbocharger For BMW N20 2.0L TUR-102737-MTN

Remanufactured OEM w/ Two Year Warranty: Turbochargers Direct Remanufactured OEM Mitsubishi Turbo For BMW 228i 320i 328i 428i 528i X1 X3 X4 X5 Z4 N20 TUR-102737-TDR

New Aftermarket w/ Three Year Warranty: New Factory Turbochargers Replacement Turbo For BMW 228i 320i 328i 428i 528i X1 X3 X4 X5 Z4 N20 TUR-102737-FTN

Fits:

2014-2016 228i

2015-2016 228i xDrive

2012 320i w/ Prod. Date of 11/1/2012 or later

2013-2018 320i & 320i xDrive

2012 328i w/ SULEV Emissions

2012 328i w/o SULEV Emissions AND w/ Prod. Date of 7/1/2012 or later

2013-2016 328i & 328i xDrive

2014-2016 428i & 428i xDrive

2015-2016 428i Gran Coupe & 428i xDrive Gran Coupe

2013 528i & 528i xDrive w/ Prod. Date of 7/1/2013 or later

2014-2016 528i & 528i xDrive

2012 X1 sDrive28i & xDrive28i w/ Prod. Date of 7/1/2012 or later

2013-2015 X1 xDrive28i & sDrive28i

2013 X3 sDrive28i & xDrive28i w/ Prod. Date of 4/1/2013 or later

2014-2017 X3 xDrive28i & sDrive28i

2015-2018 X4 sDrive28i & xDrive28i

2016-2018 X5 xDrive40e

2013 Z4 sDrive28i w/ Prod. Date of 9/1/2013 or later

2014-2016 Z4 sDrive28i

Another turbocharger-specific issue on the N20 is the turbo’s oil feed line. Just like any other vehicle, we strongly advise you clean or even replace the oil feed and return lines when you install a new turbocharger, to ensure a reliable supply of clean oil to the center bearing housing. Early N20 models were the subject of a BMW Technical Service Bulletin (TSB SI B11 11 16) to address an internal oil leak that causes affected cars to emit a plume of blue smoke for 10-20 seconds after a cold start. This was due to oil continuing to flow into the turbo after the engine is shut off, and leaking into the exhaust housing. The fix is a replacement oil feed line (BMW part number 11 42 8 678 840, available here) with an integrated check valve that cuts off the oil supply when it measures too much oil pressure inside the turbo itself. The BMW factory warranty on the original oil feed line has been extended to 10 years or 120k miles, and affects the following vehicles:

2012 328i Sedan with a production date between 10/19/2011 and 7/20/2012

2012 and 2013 528i Sedan with a production date between 8/22/2011 and 6/27/2013

2012 and 2013 528i xDrive Sedan with a production date between 6/7/2011 and 6/28/2013

2013 X3 xDrive28i with a production date between 12/8/2011 and 3/28/2013

2012 and 2013 Z4 sDrive28i with a production date between 6/9/2011 and 2/26/2013

We have multiple replacement turbocharger options for the N20 and N26 – new or remanufactured, OEM or aftermarket – as well as turbos for the N54, N55, S55, B58, N62, LBZ, ISB and any number of other indecipherable 3-digit product codes. Contact us for knowledgeable assistance in getting the correct replacement turbo for anything that had one from the factory!