Common Problems on the BMW N55

The N55 is the successor to one of the most legendary European engines of all time. No matter if it’s a 135i or a 335i, these cars are some of the most solid and tuneable out there. 

However, although it may be considered much more reliable than its older brother, the N55 still has some skeletons in the closet you should keep an eye out for, whether you’re an owner or prospective buyer.

N55 engine bay

VANOS Solenoid Failure

Since its introduction to BMW models in 1992, VANOS systems provide variable valve timing on BMW’s engines to increase performance and smooth operation. As with any complicated part, VANOS. The N55 is not exempt from this issue. VANOS solenoids can wear down or become dirty and prevent the flow of oil past them. The flow of oil to the cam gears is what allows the timing to be adjusted, and when this is slowed or stopped, it can cause a host of problems for the car. Some of these symptoms can include a rough idle, bogging at low RPM driving, loss of power, and decreased fuel economy. These problems are often accompanied by a check engine light and occasionally the car falling into a limp mode. 

High Pressure Fuel Pump Failure

While more common on the early motors, every N55 owner should know the symptoms of a failing high pressure fuel pump (HPFP). An o-ring separates the fuel pump between the fuel half and the oil half, and when this o-ring degrades over time, it can cause a major loss in fuel pressure. 

As you can imagine, when the engine can’t get adequate fuel, bad things happen. This problem can present as trouble starting the car, hesitation when accelerating, stalling,. Fortunately, while it will need to be replaced, there are a few things you can do to extend the life of your HPFP. Using high quality oil with additives can prevent the accelerated wear on your o-ring, and maintaining your vehicle’s  health with regular changes can help as well. 

Water Pump Failure

The water pump is one of the most vital parts of your engine, keeping coolant circulating and preventing your engine from overheating. The N55 has an electric water pump, unlike most cars where the pump is driven by the engine. These electric pumps have a higher probability of failure over a traditional one, and the problems can worsen over time without proper maintenance. 

Water pump failure is most commonly noticeable in the overheating of the engine, which can lead to expensive repairs. You can also often hear the cooling fans working overtime to make up for the pump, and the pump will often emit a high-pitched sound when the pulley or bearings loosen. Coolant steam and its sweet smell are your final warning sign before things turn catastrophic if they haven’t already. To help prevent this, regular maintenance should be carried out on the cooling system and you may want to replace the pump with 60,000-90,000 miles, as the pump will fail eventually. 

Oil filter housing in engine bay

Oil Leaks

There’s two main spots that the N55 loves to spring a leak from. One is the oil filter housing gasket, which becomes less effective over time. Of course, oil wears down every part, but a particularly weak part such as this gasket is more susceptible to total failure and leaking oil. This leak is often onto the drive belt, which can cause serious problems such as wearing down the belt prematurely or even snap the belt, which can (in rare cases) lead to total engine failure. The other major culprit is the valve cover and its gasket. A minor leak here may be safe to drive on and cause little to no damage over a short period of time, but these parts are relatively inexpensive, and failure to replace them with a small leak can allow the leak to grow and eventually allow oil to reach motor mounts and even belts. 

Charge Pipe Problems

The factory charge pipes on the N55 are made of a plastic material initially resistant to heat and pressure, but with consistent heat cycles and boost pressure, this plastic can start to crack and eventually leak. When this happens, you’ll notice a major loss of power and throttle response, as well as the car possibly going into a limp mode state. This problem is much more common with increased boost levels, but can still happen to a completely stock engine. So even with stock boost, a beefed up plastic or even a metal charge pipe may be a smart investment to prevent boost leaks in the future.

Is the N55 worth the trouble? 

The N55 was essentially BMW’s response to the unreliability of the N54, and it is a much more solid motor. However, it is still a complicated, high tech, and high performance engine that needs to be treated as such. The earlier N55 motors have slightly more issues, but even so these engines will run long and well with proper maintenance from the owner. 

When owning or buying an N55 powered car, it’s important to take the car in for an inspection from an expert to make sure the motor is in good health. With the right owner, these motors can be as reliable as any other.

N55 Service and Inspections at Alex’s Autohaus

Alex’s Autohaus is your premier destination for BMW and European car service in the Salt Lake Valley. Our ASE certified technicians will keep your Bimmer running strong, and know what to look out for on your specific vehicle. With our help, we can keep your N55 buttoned up and your car on the road. Call or schedule an appointment with us online today!

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