BMW's N20 engine pitfalls: Timing and oil pump woes

From a market perspective, starting in 2011, the N20 engine was meant to succeed naturally aspirated six-cylinder engines with moderate power output, which could no longer meet emission standards. BMW's model range therefore gradually incorporated turbocharged petrol units, both four- and six-cylinder, featuring direct fuel injection.

The N20 engine design was installed in many BMW models from 2011 to 2016 and exclusively in cars of this brand. The trade designation 18i indicates a power output of 156 BHP, 20i reaches 184 BHP, and 28i was meant for the most powerful version, with a power output of 245 BHP.

Below is a list of cars with the N20 engine along with their nomenclature:

• Z4 sDrive18i / 20i / 28i (E89),
• X1 xDrive / sDrive20i / 28i (E84),
• X3 xDrive20i / 28i (F25),
• X3 sDrive18i (F25),
• X4 xDrive28i (F26),
• X5 xDrive40e (F15),
• 125i (F20),
• 220i / 228i (F22),
• 320i / 328i (F30),
• 320i / 328i GT (F34),
• 420i / 428i (F32),
• 520i / 520Li / 525Li / 528i (F10).

The article continues below the video

It is also worth noting that the N20 engine comes in two capacities: 1.6 litres and 2.0 litres, but the smaller one is rarely found in Europe. The 1.6-litre N20 engine should not be confused with the 1.6-litre engine fitted around the same period in Mini cars. This is actually a unit developed with PSA from the Prince family, which I have thoroughly described in the text below.

The N20 featured all the ecological "innovations" that began to appear in other petrol engines at the time. However, BMW reached a higher level of sophistication with the engine commercially named TwinPower Turbo.

It features double Vanos, which means variable valve timing on both the intake and exhaust sides. Additionally, it includes a twin-scroll turbocharger, meaning it has dual channels (hence the TwinPower Turbo moniker), allowing it to spool up faster than a traditional one. There is a third-generation Valvetronic system, which enables continuous valve lift regulation, eliminating the need for a traditional throttle, although the N20 engine has one employed mainly during startup and warming phases, or if Valvetronic fails.

The start-stop system aims to promote fuel economy, and an electric water pump is used for faster and fully controlled temperature regulation. The N20 is a lightweight design made from aluminium, with two camshafts within the head, a chain-driven timing system, and an additional chain driving the oil pump.

The N20 engine underwent technical modifications in mid-2013, preparing it for the Euro 6 standard. Among other changes, pistons and the fuel system were updated, although Bosch remained the supplier throughout the production period. The turbocharger's control was also adjusted from vacuum to electric.

Initially, a major and severe concern for car users with this engine was the timing drive. In theory, it was a simple design with a chain, hydraulic tensioner, two variable phase gears, and several guides.

Unfortunately, after the first oil change, the chain often began making noise. In many cases, it didn’t last more than 60,000 kilometres. If the car was mainly driven on motorways or serviced against the manufacturer’s recommendations (with more frequent oil changes), the system lasted longer but still rarely exceeded 100,000 kilometres. In 2017, users in the USA even filed a class-action lawsuit against BMW.

The primary issue was the durability of the parts, but the problem of fuel mixing with the oil and uncontrolled pre-ignition, caused by crankcase fumes, was also significant.

If the engine operated under reasonably constant load (e.g., on the motorway), the system managed, but city driving or idling, as well as frequent starts and stops from the start-stop system, proved destructive to the timing drive.

A stretched chain wears down the plastic guides (polycarbonate), and fragments end up in the oil, not only degrading it further but causing issues for the tensioners, Valvetronic system, or oil pump module. If that weren't enough, the original guides were so fragile they cracked, sometimes immediately blocking proper oil flow, not to mention the sudden loosening of the chain.

Over time, specifically in 2015, the manufacturer recognised the issue and improved the quality of the timing drive components, making cars from this year considered less problematic in this area. Unfortunately, the overall mechanism’s durability remains poor, as it results not just from the strength of the parts but also from the engine operating with frequent pre-ignitions. Therefore, it is advisable to replace the chain and all related parts every 100,000 kilometres.

Following the timing chain problems, a second issue emerged concerning the oil pump, specifically its drive. What the engineers devised at the lower part of the engine can be described in various ways - from a technical marvel to madness.

Beneath the engine block lies a mechanism with a balance shaft for the engine, hence the unusual shape of the oil pan made from plastic. The balance shaft module connects to the oil pump, receiving power via a gear from this shaft. The entire module is driven by a small chain, obtaining power from the crankshaft.

However, it was not the complex pump and balancing shaft module that proved weak, but its simple drive. Both the tiny wheel at the crankshaft and the thin chain barely lasted 100,000 kilometres. This caused the module to stop, thus halting the oil pump and leading to engine seizure.

If that were not enough, there is also a hydraulic tensioner in this simple drive, which, operating with old oil, does not properly tension the chain, causing wear to the plastic guides.

The original set of the module drive costs 850 PLN (~£160), while a substitute can be purchased for half the price. It is necessary to replace this alongside the entire timing drive set, which costs between 1500 and 2500 PLN (~£283 to ~£471), depending on the manufacturer, for a substitute. The original set is not much more expensive, provided you do not order variable valve timing gears, which have prohibitive prices.

Variable valve timing gears are also problematic. Over time, they begin rattling and struggle to reach full power. Ideally, they should be changed with the chain, but not everyone opts for this. While the prices of original parts are intimidating, substitutes can be purchased for under 100 PLN (~£20).

In essence, it’s not only the timing drive of this engine that should be replaced every 100,000 kilometres. Evidence suggests that at this mileage, many areas require review, and adhering to this rule ensures the car will run long and trouble-free. I will explain which areas are involved.

Engine N20 seizing is not always a rapid process; often it is slow. One cause is excessive petrol mixing with the oil in substantial quantities. This is not only due to poor lubrication, and thus excessive loads that injectors attempt to compensate for with excess fuel, but also a fundamental reason – faulty sealing of the high-pressure pump. Petrol leaks directly into the valve cover.

Another critical point is the pump drive in the form of a pusher that connects it to the camshaft’s cam. If you hear tapping from this area, it is this pusher that requires replacement. It is advisable to do this, along with the aforementioned sealing, every 100,000 kilometres. Fortunately, the injectors are durable and do not cause issues.

Additionally, note that if there is excess fuel in the oil, the oil level sensor fails to detect it, often ceasing to display the level altogether. Unfortunately, the designers have abandoned the traditional dipstick in favour of electronics. Thus, users often receive no indication that something is amiss or they think the only issue is a sensor malfunction.

Excess petrol in the oil results in combustible fumes escaping through the breather into the cylinders, where they burn uncontrollably, causing strong vibrations and carbon buildup. These vibrations certainly contribute to the faster destruction of the timing chain, completing the circle.

Oil leaks are common, including from the oil pan, heat exchanger seals, and the valve cover, which often cracks after 100,000 kilometres, more frequently after about 150,000 kilometres. The cost of a new original is about 1900 PLN (~£378), and aftermarket ones can be bought for around 600 PLN (~£120).

This component is surprisingly advanced, extensive, and crucial for the operation of interconnected components, so it’s worth spending the money to purchase the original. Add this to a set of gaskets for about 250 PLN (~£50) plus labour, making the bill amount to 2500 PLN (~£471). Now it is easier to understand why these engines are often literally covered in oil.

In extreme cases, oil leaks onto the exhaust manifold, causing unpleasant smells or even smoke, and onto the alternator belt, which, if broken, winds around the pulley. Not just the pulley, but the entire block sealing ends up needing replacement.

Leaks also occur in the vacuum pump, with oil entering the vacuum system, but this does not affect the braking system's operation; rather, it affects the turbocharger. The vacuum pump should be checked for leaks every approximately 100,000 kilometres. If it needs replacing with an original, the operation will be very costly. Parts alone cost about 2700–3000 PLN (~£537-£597).

A prevalent issue with the N20 engine and its turbocharger is the characteristic ringing, which most often results from play in the turbo control lever (at the wastegate valve), regardless of vacuum or electric control. Neglect in this area results in minor issues with turbocharger operation. Specialists fix it, although there is no factory repair technology, but an entire actuator (approx. 1500 PLN ~ £283) can be replaced.

If the engine begins to vibrate strongly, the culprit is usually the Valvetronic system, but it is not at fault itself. The real cause is a weak battery, which due to the electronic Valvetronic control, requires full efficiency to set all mechanisms relative to the crankshaft's position before starting the engine. If it is weak, this does not occur, resulting in vibrations. If vibrations arise during the ride, it is worth stopping, turning off the engine, and after a few seconds, starting it again. If the vibrations cease, it confirms the battery needs charging or replacement.

The reliability of the entire Valvetronic system is estimated to last around 300,000 kilometres. The actuator with a worm gear is the first to wear out, costing about 2000 PLN (~£397) (original). Fortunately, replacements can be found for about 700 PLN (~£139). Over time, the eccentric shaft wears, costing over 4000 PLN (~£796). However, this mainly affects poorly serviced cars with mileages over 350,000-400,000 kilometres.

After purchasing a car with higher mileage, it’s worth proactively replacing the electric water pump, especially if you regularly travel long distances on motorways. Although the failure is not common, it manifests as intensive fan operation, and if it occurs, you should not continue driving. Fortunately, substitutes are not excessively expensive (~£239), while an original will cost three times more.

Tuned engines are very risky, especially when simple chiptuning aims to achieve the power of a 28i from a 20i. These versions differ, among other things, in piston shape, and hence compression ratio. Such tuning not only escalates the phenomenon of petrol mixing with the oil but also results in serious failures, such as seizing or cracking of the head. It also increases the risk of injector and timing drive failures.

In summary, the N20 engine is not particularly successful, and its main problems are the timing drive and oil pump. It is believed that from the 2015 production year, these problems no longer occur, but according to the principle of limited trust, it is still recommended to replace the timing drive and check the described areas every 100,000 kilometres. It is also advisable to change the oil frequently because workshops with extensive experience confirm that with diligent servicing, many customers have run their cars trouble-free for over 200,000 kilometres and even about 300,000 kilometres.

So is it worth buying a car with this engine? It has good power, dynamics, and reasonable fuel consumption, so if you purchase a well-maintained car and are aware that the engine requires ongoing attention, which isn’t cheap, nothing stands in the way. This also applies to older model years where the timing drive was replaced with an improved version, although personally, I would still recommend replacing it right after purchase along with reviewing all critical points. Unfortunately, it won't be inexpensive.