The four-cylinder BMW N46 engine was used to power various marques of BMW from 2003 to 2012. BMW developed this versatile engine off the back of the previous N42 generation. While it did incorporate newer, more advanced technology, it was also tasked with improving the brand’s reputation for reliability.
The BMW N46 was a new-generation engine, but it did suffer from some common problems. These included high oil consumption, vibration caused by the VANOS variable valve timing system, leaking valve stem seals, and rattling noises caused by worn timing chain tensioner and guides.
BMW used the N46 engine in the BMW 316i, 316ti, 118i, 318i, 318ci, 318ti, 320i, X3, SDrive 1.8i, and the BMW 520i between the years 2003 to 2012. BMW had recently suffered some setbacks in its overall reputation for reliability and the next-generation BMWs powered by the N46 engine were designed to start the drive to improve this.
The BMW N46 Significantly Improved The Previous N42
In 2021 BMW achieved a JD Consumer rating of 80/100; however, in the early 2000s, the situation was very different. In 2006, on average, BMW vehicle owners experienced 212 problems per 100 vehicles sold compared to the winning brand, Lexus, of 136 problems per 100 vehicles sold.
The 3 series has long been among the most successful BMW models. It started production in 1975 and has been BMW’s most popular model ever since. Being one of the most crucial revenue earners for BMW made it extremely important to fix the reliability problems of the previous generation N42 engine.
The N46 included the following upgrades and changes:
- BMW upgraded the engine management system to a Bosch MV17.4.6 engine unit
- BMW installed double overhead camshafts
- The valves per cylinder were increased to four
- The crankshaft was modified
- The engineers modified the Balance Shafts
- The Connecting Rods (Pleuel) were modified
- BMW improved the Vacuum Pump
- The Roller Cam was strengthened
- The Cylinder Head Cover was revised
- BMW incorporated two gear balance shafts
- The intake manifold was adjusted
These changes resulted in a more refined engine with smoother power delivery. Simultaneously the BMW N46 improved its eco-credentials by boasting lower:
- Fuel Consumption
- Exhaust gas levels
- Carbon monoxide
- Hydrocarbon (HC)
- Nitrogen oxide (NOx) levels
The N46 also emitted lower, carcinogenic benzene emissions in full-load operation.
The displacement and output of the N46 were increased over the engine’s lifetime.
| Year | Displacement | Power | Torque |
| 2003 | 1796cc | 85kw @ 5,500rpm | 175Nm @ 3,750rpm |
| 2004 | 1995cc | 110kw @ 6,200rpm | 200Nm @ 3.600rpm |
| 2006 – 2012 | 1995cc | 125kw @ 6,400rom | 210Nm @ 4,100rpm |
The BMW N46 Engine Had Some Faults
As with any engine, there have been a few issues that have appeared as a pattern with the BMW N46.
BMW N46’s Developed A Reputation For High Oil Consumption
The causes of the N46’s high oil consumption were often a result of prematurely worn valve stem seals.
The failure of the N46’s valve seals was mainly caused by a clearance problem between the valve and valve guide located in the cylinder head.
A clue that this is becoming a problem is increased oil consumption and the appearance of puffs of white, grey, or bluish smoke from the exhaust pipe when accelerating. It is particularly true after sitting with the engine idling for a while (such as at the traffic lights) and then accelerating away.
When the N46 first arrived you actually needed to remove the N46 head to change the valve seals. The situation has been dramatically improved, and now with the correct tools, the seals can be replaced without removing the head.
An Irritating Vibration From The N46’s VANOS System
A solenoid in the VANOS regulates the amount of oil pressure being applied which, in turn, controls the movement of the cam gear outward or inward, which sets the valve timing.
Sometimes the VANOS system caused vibration and a “rattling” sound from the unit. Unfortunately, this is a common problem on 3 Series BMWs dating back to E36 Vanos units. Owners could sometimes mitigate the rattling problem by cleaning the N46’s VANOS variable valve timing system.
The process to clean the VANOS system involved:
- Removing the piston from the VANOS cylinder
- Spraying brake cleaner on both the VANOS piston and cylinder
- Apply oil to the piston and cylinder and reinstall the piston
- Checking that the piston moves freely
- Reinstalling the unit
Below is a great video tutorial on cleaning the Vanos solenoid.
A competent DIY car owner could complete this work. However, it should be noted that cleaning the VANOS often will not resolve the rattle entirely and you will then need to replace several of the gears.
The VANOS solenoid very rarely failed. However, it could leak oil from the electrical connector in some cases, which would require it to be replaced.
Rattling Noise Caused By The Timing System
One of the engine components which has remained in the internal combustion engine from the earliest days is the timing chain.
An Internal combustion engine needs three things to work.
- Fuel
- Air
- Spark
The Fuel and Air mixture is injected at the optimum point in the pistons cycle. Simultaneously the ignition sends an electrical charge to the spark plug, which ignites and causes the fuel/air mixture to combust. The subsequent expansion of the gases forces the piston down and onto the next cycle.
The N46 timing chain is positioned in front of the N46 motor. It is attached to gears that connect to various mechanical components, including the crankshaft and camshaft.
The N46’s timing chain must rotate smoothly around the gears for the engine to fire.
As the name implies, the chain tensioner and guide rail keep the timing chain at the correct tension and running smoothly.
Unfortunately, BMW used a plastic guide rail which was known to fail. This is a significant problem and you will not find issues with the timing chain guide rails/tensioners on older BMWs.
Indications that the N46 tensioner or the guide rail is failing may include the following symptoms:
- Engine rattles while idling
- Noisy engine at the front, particularly from a cold start
- Engine misfires or runs poorly
- Metal shavings are found in the oil
- The N46 engine won’t start or fails
- The N46 check engine light is on
- Error codes for camshaft sensors appear when the sensors are OK
How Do You Replace The Timing Chain?
Very rarely will a BMW owner ever have to replace a timing chain. Timing chains are designed to last the lifetime of the vehicle, however, things do happen sometimes, and the N46 had more timing chain issues than most other BMWs.
I do not recommend that the hobbyist DIYer attempt to replace the timing chain unless you have significant experience with more serious DIY work. Here are the general steps on how to do it:
- Remove the rocker cover
- Remove the camshaft
- Remove the VANOS unit
- Remove the whole cassette, which contains the timing chain and guides
- Cylinder number one needs to be at Top Dead Centre (TDC) before installing the new chain
- The timing chain and guides for the BMW N46 engine are sold as one unit in a cassette and are reinstalled in the reverse procedure as you removed it
- Changing a timing chain is best left to someone with BMW engine experience.
Here is a great video tutorial on replacing the N46 timing chain.
The N46 engine service bulletin recommends that the timing chain be replaced every 60,000 miles (100,000 km). I personally think this is insane, 60,000 miles is far too little for a timing chain.
My recommendation is to be aware of the warning signs of timing chain and chain tensioner issues. If you allow these problems to develop then they can damage your engine. A broken timing chain will result in the piston and valves colliding, which will cause damage to the cylinder head, valve, piston, cylinder, and camshaft. It is a sure-fire way of ruining your day.
The BMW N46 Transmission Needs Servicing
BMW models, equipped with the N46 engine, were offered in manual or automatic transmissions.
A common issue of the N46 engine was that the transmission output shaft seal needed to be replaced.
When an output shaft leaks, it could release transmission fluid, allowing debris into the output shaft.
A leaking output shaft seal could develop as the vehicle became older and the seals became harder. The shaft seal was also vulnerable to being hit and dislodged. If an output shaft seal does leak, it must be repaired immediately.
The BMW N46 Engine Used Plastics In Various Systems
If you have read any of my other critiques of BMW engines, you know that usage of plastic parts in the coolant system is an epidemic. BMWs as far back as the E36 Series needed their entire coolant system to be replaced every 50-60,000 miles or else things would randomly start cracking. The N46 unfortunately is no different, it used plastics in the engine, cooling, and ventilation systems, and they can become brittle with age and eventually crumble.
The oldest N46 engines are almost 20 years old, so replacing all the fittings as a preventative measure is always a good idea.
Conclusion
The BMW N46 engine fulfilled its mission in that it helped BMW to re-earn its reputation as a manufacturer of high-quality, reliable vehicles. Despite this, these vehicles powered by an N46 powerplant are now at least 10 years old, and, understandably, parts that are vulnerable to wear may need to be replaced.
If you’re thinking of buying a car powered by the N46 engine, with more than 60,000 miles on the odometer, have someone who knows these cars check it out. It’s also worth getting to know a BMW specialist mechanic to keep your vehicle running smoothly in the future.
References
https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-timing-chain
https://www.e46fanatics.com/threads/need-to-clean-and-potentially-replace-exhaust-vanos.1176633/