The Most Common BMW N55 135i, 235i, 335i, 435i, 535i Engine Problems
N55 Common Engine & Reliability Problems
For those in the market looking to purchase a BMW 135i, 335i, or 535i one important aspect to consider is reliability. In this post, we intend to highlight the most common problems with the N55 platform; please keep in mind – this is not an exhaustive list of every single potential problem. All cars and engines will have problems at some point. Some problems are unique and only affect a small number of cars, while in this post, we will address the most common engine problems that affect a larger number of N55’s.
Common N55 Engine Problems
- Valve Cover Oil Leak
- Water Pump Failure
- Leaking Oil Filter Housing Gasket
- VANOS Solenoid Failure
- High Pressure Fuel Pump Failure (HPFP) – Mostly older models
1. N55 Valve Cover/Valve Cover Gasket Oil Leak
Similar to the N54, a leaking valve cover, valve cover gasket, or PCV valve are among the most common problems with the BMW N55 engine. The rubber valve cover gasket is prone to degrading over time; typically rubber with high temperatures, and constant heating/ cooling do not mix well. Eventually, the rubber gasket begins to crack apart, resulting in oil leaks and potential build-up of oil in your engine.
Due to the relatively high operating temperatures of the N55 the valve cover develops similar issues. The valve cover is made of plastic and the high temperatures cause the valve cover 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 (though this may vary significantly). However, due to the excessive labor required to access the valve cover gasket, it is highly recommended you replace the valve cover as well. Whenever you remove the valve cover you should always replace the valve cover gasket.
N55 Valve Cover and Gasket Leak Symptoms:
- Low engine oil light
- Burning oil smells, or smoke coming from valve cover area
- Oil on spark plug threads
Another issue that ties into the valve cover and gasket is the Positive Crankcase Ventilation Valve (PCV valve). A PCV valve uses the engine vacuum to pull any blow-by gases out of the crankcase, and is integrated into the valve cover. Higher pressures and fatigue of the PCV valve lead to eventual failure, and this is a fairly common issue with the BMW N55. Due to the fact you must remove the valve cover and gasket to access the PCV valve you may want to consider replacing your valve cover, and as always, the valve cover gasket should be replaced. You can learn more about the PCV valve, and how to diagnose a failing PCV valve here:
Replacing N55 Valve Cover and Gasket
As your valve cover, gasket, and PCV valve are all in the same area, if any one needs repair, it is never a bad idea to replace all three as preventative maintenance. The parts are relatively inexpensive compared to the labor required, and may prevent running into additional issues in the near future. Whenever the valve cover is removed you should always replace the valve cover gasket, even if it appears to be in good condition.
Should You Replace a Leaking Cover or Gasket?
This subject is up for debate. A minor leak from the valve cover and/or gasket does not cause any significant, immediate risk to performance or longevity of the N55. However, the oil may be leaking onto belts or engine and transmission mounts. Over-time this may cause these parts to wear down prematurely and lead to additional expenses. My 335i currently has 103k miles, and the valve cover gasket began leaking around 80k miles. Up until roughly 95,000 miles it was a relatively minor leak that was not dripping oil onto any engine parts, however, it has recently become worse. With that being said, replacing the valve cover, gasket, and PCV valve is next on my list of things to repair.
Replacement Cost: $40 for the valve cover gasket, $270 for the valve cover, gasket, and hardware. Due to the intensive labor to access the valve cover, the cost of replacement at the dealer is roughly $1300 and $1000 at independent shops (this can vary quite a bit, however).
Buy it on Amazon: Valve Cover With Gaskets For 2011+ BMW N55
DIY Difficulty: Intermediate. This is not a complex DIY, but it does require removing a lot of parts to access. For an intermediate skilled DIY’er this can take up to 8 hours to complete.
2. N55 Water Pump Failure
Problems with water pumps do not only affect the N55, but are a widespread problem amongst most BWM engines. Water pumps are responsible for circulating coolant throughout the N55’s cooling system in order to cool engine temperatures. BMW uses electric pumps that are driven by a composite impeller, which do not have a very long lifespan. It is important to note – the thermostat is also a common point of failure. Due to the excessive labor to replace a water pump it is recommended you replace the thermostat along with the pump.
To reference our experiences with the N54 (same water pump) our 535i is on its third water pump; the original pump failed at 52k miles, and the second pump at 84k miles. The water pump in Jake’s 135i failed at 33k miles, while the pump on my 335i lasted until 95k miles. The longevity of these BMW water pumps may vary significantly, with failures commonly cited as early as 30-40k miles while others may last more than 120,000 miles. On average, if your original pump and thermostat last until 100,000 miles they are likely soon on their way out.
BMW water pumps typically do not show any symptoms before failure, but rather, fail quite suddenly. If the pump is slowly failing electrically, this can simply be tested by examining the coolant flow in the cooling system; a failing pump will not flow coolant at the intended pressure. The following signs may indicate your N55 water pump has failed.
Signs of N55 Water Pump Failure:
- Engine overheating significantly – usually rapid over-heating once the pump fails
- Cooling Fan running full speed (noisy)
- Coolant boiling out of coolant cap
N55 CEL Codes for Failing Water Pump:
- 2E81, 2E82, 2E83, 2E84, 2E85
- Remember to check fuses
N55 Water Pump Replacement
Due to the rapid engine over-heating caused by a water pump failure it is important the water pump is replaced immediately, otherwise the car should not be driven. The OEM water pump is roughly $450, and installation will likely cost an additional ~$500. Replacing the water pump is not overly challenging, however, it is a time-consuming repair and it is important to properly bleed the cooling system afterwards.
Replacement Cost: $325 for water pump, ~$500 installation
Replacement Part: Water Pump for E-series N55
DIY Difficulty: Intermediate to Advanced
3. N55 Leaking Oil Filter Housing Gasket
Yet another weak point of the N55 is the Oil Filter Housing Gasket (OFHG), which begins to degrade and leak oil with age. An OFHG leak is not a severe problem in the short run, however, not to overly scare anyone, the oil commonly leaks onto the belt tensioner and drive belt. Oil dripping onto belts is never a good thing. This may lead to the belt snapping or slipping off the pulley, which can cause damage to other engine parts and, in the worst case, may even be pulled into the crankshaft seal (front main seal). If the belt makes it past the front main seal and into the engine internals you have a severe problem at hand. I don’t intend to scare anyone with this information, as it’s not common for the belt to be pulled into the N55 engine, but it IS possible.
This can all be avoided in most cases – of course there is the possibility of belts slipping or shredding for un-related reason – by simply replacing the oil filter housing gasket.
Additionally, if the OFHG leaks for a long period of time or leaks severely there is potential for cross-contamination of the oil and coolant. The Oil Filter Housing Gasket is roughly $15, so it is a cheap fix for something that may potentially lead to significant problems down the road. As with most BMW repairs, it can be a lengthy process to replace the OFHG, which means it may end up relatively expensive if you’re paying a mechanic. However, replacing the leaking gasket is important as it may help prevent issues down the road.
Replacement Cost: $10 for gasket (https://amzn.to/2QjlI0T), ~$400 for labor
DIY Difficulty: Intermediate – Roughly 4 hours labor
DIY Guide: http://f30.bimmerpost.com/forums/showthread.php?t=1372527 (F30 chassis)
4. N55 VANOS Solenoid Failure
VANOS stands for Variable Camshaft Timing, which is a valve timing system used, in conjunction with Valvetronic, on the BMW N55 engine. To keep it short, BMW VANOS (or Double VANOS on the N55) adjusts the timing of the intake and exhaust camshafts based on the engine speed and throttle opening. The basic point of this system is to improve idling, smooth the power, and as the engine speed increases the double VANOS system boosts torque, increases fuel economy, and lowers emissions.
The VANOS Solenoids are always working, so they typically fail due to wear and tear and/or old-age. However, they may also become coated in oil and cause problems due to being too dirty or “gunked up”. It should also be noted – on early model N55 engines, between 2010 and 2012, the VANOS bolts were recalled. The bolts may potentially become loose or break; when the bolt breaks it typically drops into the engine oil pan leading to additional repair time and costs. As mentioned, this was recalled and should no longer be an issue.
N55 Failing VANOS Solenoid Symptoms:
- Loss of Power and Torque
- Engine hesitation and bogging
- Rough idle, bouncing RPM’s
- Starting issues and potential stalling of vehicle
- Limp mode
The above symptoms are general and do not definitively point towards VANOS solenoids. For example, old spark plugs and/or ignition coils may cause similar issues such as loss of power, engine hesitation, and rough idle. The below check engine light codes may point directly towards the solenoids, however, a code is not always present.
N55 VANOS Solenoid CEL Codes:
- 2A9A, 2A9B
- 2A82, 2A98, 2A99, 2A87
Replacing Your N55 VANOS Solenoids
Some people elect to simply clean the VANOS Solenoids rather than replace them, which typically does not completely solve the problem but rather buys some extra time. The solenoids are not tough to remove and re-install, so attempting to clean gunked up solenoids may be worth the time. Although, the solenoids are not overly expensive, so replacing the solenoids is likely the best option if you’re looking for the most effective repair.
Replacement Cost: ~$165 for each solenoid (2 required), ~$200 labor
E-Series Replacement Solenoids: https://bmwsparkplugs.com/products/bmw-vanos-solenoid-11-36-7-585-425
DIY Difficulty: Easy to Intermediate
DIY Guide: Please help us out if you find a good guide to replacing N55 solenoids!
5. N55 High Pressure Fuel Pump Failure (HPFP)
A high pressure fuel pump is tasked with the challenge of pumping fuel from the gas tank into the fuel injectors, where it is then sprayed directly into the cylinders via the N55’s direct injection. We will not spend too much time on this subject as it is primarily an issue with 2010 and early-mid 2011 model N55’s. BMW’s N54 is notorious for the countless HPFP issues experienced throughout its production. It was not until late 2011 that an effective HPFP finally solved the issue. You guessed it, despite countless attempts by BMW to fix the HPFP, in 2010 and 2011 when the N55 was first introduced BMW still did not have an official fix. So, the N55 was introduced with the same faulty HPFP as the N54.
However, unlike the N54’s HPFP which was granted a 10 year, 120,000 mile extended warranty, the N55 does NOT have an extended warranty on the HPFP. A majority of the faulty HPFP’s installed in early model N55’s likely failed under warranty and were replaced with the newest design that resolved the issues. There are still be some older N55’s out there running on the outdated HPFP, so this is something that may go wrong.
Despite the many misconceptions that BMW’s as a whole are unreliable, the BMW N55 is actually a fairly reliable engine. The four most common problems with the N55 are, in no specific order, the valve cover and gasket, water pump, oil filter housing gasket, and VANOS solenoids. None of these are necessarily major issues, and most of the parts are not expensive. However, and I think this is where the misconceptions about BMW reliability come into play, the repair bills can begin to add up if you always service your car at the BMW dealership or independent repair shops.
Also, do keep in mind, this is not an exhaustive list of things that can go wrong with the N55, and simply because something is on the list does NOT mean it will indefinitely be an issue. With that being said, we are examining the “average” N55 and what goes wrong with the “average” engine. There are plenty of N55’s with 100,000 miles that have not cost a dime in out of pocket repairs, while others with significantly fewer miles may cost thousands a year in repairs. It all comes down to how well you maintain your N55, and to some extent, the luck of the draw. Overall, the BMW N55 is a reliable engine that can be easily tuned to make impressive horsepower and torque.