The N46 engine by BMW is one of those universally hated engines. Wondering why? Well, for one, the second-hand, high mileage owners usually cashed out their wallets on all the repairs and secondly, the N46 replaced some of the legendary 4 cylinder engines (M44 for example) that were featured in the E46 BMW 3 Series.
Here are the most common BMW N46 engine problems:
- Timing chain and tensioner failures
- Various and serious oil leaks
- Cam and crankshaft sensor failure
- VANOS solenoid problems
- Valvetronic and VVT motor failures
To find out more about these problems, I contacted 3 past owners of BMW E90s with this engine and I did thorough research online. Here is more details about each problem I listed above.
BMW N46 Engine Specs & Applications
Before we get into all the concerns surrounding this engine, it’s important that you know the basics of the engine construction and the cars that feature it.
The N46 engine has a displacement of 1.8 or 2.0 litres, depending on the version (N46B18 is the 1.8 and the N46B20 is the 2.0). Both variants feature 4 cylinders in a straight four configuration.
This engine uses direct fuel injection and BMW’s Valvetronic valve timing technology, which makes sure that the valves are adjusted continously.
All variants of the engine are naturally aspirated, meaning you don’t need to worry about any turbocharger relates problems. Talking about turbo’s, let’s cover the power and torque figures next.
- N46B18:
- Power: Approximately 115hp / 85 kW
- Torque: Approximately 175 Nm at 3750 rpm
- N46B20:
- Power Output: Approximately 127 to 170 hp (depending on the variant)
- Torque: Approximately 180 to 210 Nm
The N46 engine can be found in the following BMW models:
- 1 Series – E81/E82/E87/E88 with the 120i badge made from 2007 to 2011
- 3 Series – E90/E91/E92/E93 with the 320i badge made from 2007 to 2013
- 5 Series – E60 with the 520i badge made from 2007 to 2010
- X1 Series – E84 with the xDrive 18i badge made from 2009 to 2015
- X3 Series – E83 with the X30 2.0i badge made from 2007 to 2010
Common BMW N46 Engine Problems
I listed all the common engine problems for you at the beginning, but I’m sure you want to know more. Here’s more detail for each of the problems.
Timing chain and tensioner failure
They say the apple doesn’t fall for the tree and in this case it’s not good news. Just like the N47 engine I wrote about recently, the N46 engine also suffers from timing chain problems.
This is most evident in early model years of the N46 and the main problem is timing chain stretching. This occured mainly as a consequence of timing chain tensioner failures, but the result could be catastrophic if left ignored.
The main symptom of this issue is the typical cold engine rattling, the ignition of the check engine warning light and reduced engine performance.
Like I said before, if left untreated, the timing chain could skip ahead and cause catastophic engine damage. The repairs for this issue are far from cheap and due to the outrage amongst the owners.
This lead to BMW ackonwleding these timing chain issues in some of their models equipped with the N46 engine, and in certain cases, they have extended the warranty or offered assistance with repair costs for affected vehicles.
Sensitive to engine oil type
If you’re buying a BMW with this engine, make sure that through it’s lifetime it received regular replacements of fully synthetic BMW approved oils.
A lot of owners report the importance of only pouring in fully synthetic engine oil that is recommended by BMW. Failing to do so can exaggerate and fast track some of the problems on this list.
If you just bought a N46 powered BMW, make sure, that from now on you only pour in fully synthetic engine oil.
Valvetronic motor and crankshaft sensor failures
A common problem reported on the N46 engine is the failure of the Valvetronic motor. Once this motor fails, the engine may start showing signs of all kinds of problems, including:
- Hard or no-start occurances
- Rough idling
- Power loss
- Reduced fuel economy
- Engine warning light illumination
The Valvetronic, together with the VANOS system is designed to optimize engine performance by adjusting the timing of the opening and closing of the engine’s intake and exhaust valves.
On the other hand, a failed crankshaft sensor is also common on the N46 engine and it may cause the same issues. That is understandable, since the crankshaft sensor is responsible for monitoring the position and speed of the crankshaft and is crucial for engine management, ignition timing, and fuel injection.
Cam sensor failure
Long cranking, stalling at low speeds, engine warning light. All of these symptoms indicate a failed camshaft position sensor. This is a common, but easy to fix issue on this engine.
High oil consumption and numerous oil leaks
I decided to group all of these oil leaks in a single “problem” because there’s too many common oil leaks to list one by one. Let’s dive in!
Valve stem seal oil leaks
This is the most common culprit behind the high oil consumption phenomena with this engine. If you do a quick Google search for “N46 and valve stem oil leak”, you’ll see a whole number of DIY guides and even owners printing their own 3D parts trying to solve and prevent this issue.
The most common symptom of this oil leak is incredibly high oil consumption and white or blue smoke coming out from the exhaust pipe.
Oil filter & oil cooler housing seal oil leaks
This is one of the most common oil leak areas on this engine and one that you’ll face eventually. Replacing both gaskets is a rather simple DIY job, so this one is not a deal breaker.
Oil sump gasket leaks
The oil sump gasket is bound to start leaking at one point in time on this engine. Again, if you’re into DIY repairs, this should not be too hard. Make sure you check your bottom engine protection for oil leaks regularly as this oil leak can lead to significant loss of engine oil.
Valve cover gasket oil leaks
This should be on your to-check-list when it comes to finding oil leaks on the N46 engine.
Brake vacuum pump O-ring and main seal oil leak
This oil leak location is typical for both the N42 engine and the N46 engine. Owners describe the main tell tale sign of this oil leak is the smell of burned oil when braking and after braking. You can also see hints of white smoke coming from below the hood as the oil burns off the hot manifold.
When you break, the oil leaks out of the vacuum pump on the O-ring and the main seal of the vacuum pump and it drips on hot engine components.
This is common issue so in case it hasn’t been take care off yet, expect to do the job sometime in your ownership. Luckily, it’s not a big nor expensive repair so you should be just fine.
If you want to tackle this repair on your own, I suggest you follow this amazing guide.
Dirty or faulty VANOS solenoids
VANOS solenoids on all BMW models are responsible for controling the flow of oil to the VANOS unit, which regulates the timing adjustments of the camshafts.
If you’ve ever owned a BMW than you know VANOS problems are bound to arise. Two of the common problems are dirty or faulty VANOS solenoids. Once these solenoids became dirty or faulty, they lose their ability to control oil flow.
This leads to timing issues, which results in poor idling, poor and unpredicatable engine performance and even the ignition of the engine warning light.
At the same time, also common is the deterioration of the VANOS seals. As these seals fail, they leak oil and the loss of pressure in the VANOS system can lead to rough idling, reduced power, and poor engine performance, especially at lower RPMs.
FAQ
Is BMW N46 engine reliable?
No, BMW’s N46 engine is definitely not BMWs most reliable petrol engine. One of the biggest issues we see with this engine is the timing chain and tensioner problems which can lead to expensive repairs or catastrophic engine damage.
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