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As combustion engines downsize and add electrification, BMW’s N55 inline-six has held down a respected place in the automotive industry. Available in popular models like the M135i, M235i coupe, and more, the N55 inline-six powers some of BMW’s most engaging sports cars. However, no engine is perfect, and there are a few common issues with the BMW N55, reported by real owners.

1. Fragile charge pipes

The BMW M235i used the BMW N55 inline-six until 2017
2015 BMW M235i with the N55 engine | BMW

One commonly reported problem with the N55 inline-six engine is the charge pipe. Responsible for taking hot, pressurized air from the turbocharger to the engine, it is one of the most stressed parts in a turbocharged engine. Unfortunately, this BMW engine features a hard plastic pipe that is subject to failure under heavy loads, according to FCPEuro.

Most owners recommend changing the charge pipe to an aluminum setup that will offer more durability and heat resistance versus the stock plastic unit. There are several aftermarket shops offering such a kit for between $180 and $250, and it is an easy DIY job for those so inclined.

2. Failing valve cover gaskets

One issue that probably isn’t easy for a DIYer is the valve cover gasket. Located near the top of BMW’s inline-six engine, this gasket seals the valve cover to the engine block. Unfortunately, it is one of the common failure points of the N55, but it is more messy than dangerous.

Look for oil leaks on the engine block to determine if the valve cover gasket needs replacing. When it goes, there will be oil seeping from the top of the block. As you might imagine, it can be quite a mess, and of course, you’ll be losing oil in the process. However, unless the oil is run dangerously low, there won’t be much cause for concern.

Oftentimes owners will change out the valve cover gasket before it fails to help avoid the mess altogether. Keep in mind, though, that it’ll likely cost upwards of $500 to deal with. Still, it’s better than having a mess under the hood and an engine running low on oil.

3. Water pump problems in the BMW N55 engine

Modern water pumps seem to be made of paper mache, and the BMW N55 isn’t immune to this problem. Owners report their water pumps failing in as little as 50,000 miles, despite there being no specific interval recommended by the manufacturer.

A failing water pump can be catastrophic if left unchecked. Overheating can happen quickly as coolant leaks out of the system. Worse yet, the engine can experience minor overheating events as coolant is lost, causing issues that you may not immediately notice.

4. VANOS solenoid failure

BMW M235i with N55 inline-6 engine
2015 BMW M235i | BMW

BMW’s variable valve timing system helps the engine be more efficient when cruising and more powerful when you put your foot down. Unfortunately, the electronic switch that operates the VANOS system can be a problem in the N55 inline-six.
When this happens, sluggish acceleration and poor fuel economy are the result. Because the system can’t properly optimize engine timing, the car will run rougher than normal, and the driving experience will diminish.

Overall, the N55 inline-six is a reliable engine

Despite a few minor issues, the BMW N55 engine is overall a reliable unit. With proper maintenance it can last to well over 150,000 miles, and it’ll provide plenty of smiles along the way.

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