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BMW G-Chassis 3-Series Common Problems

BMW, like nearly all manufacturers, uses chassis codes to differentiate between generations of vehicles. You’ll often hear BMW enthusiasts describe their vehicles by these chassis codes rather than the actual model name (think E30, E46, F80, etc.). With each new generation, changes are made to improve the appearance, comfort, fuel economy, reliability, and performance of each model.

The G Chassis spans a range of models in the BMW lineup, offering different body styles, engine options, and packages. In this article, we will dive into the mechanical aspects of the G Chassis 3 Series, looking at some of the most common issues owners see. 

It’s worth noting this article will only be looking at engine and powertrain problems.

Grey BMW 330i driving on highway

G-Chassis Codes Explained

Since we’re limiting the scope of this article to the 3-series, there are two codes we will be focusing on:

  • G20: 3-Series Sedan
  • G80: M3

There is a wagon (called an “estate” by BMW) variant, which is labeled G21. However, the G21 is not sold in the United States. 

G20 3 Series Common Problems

With production starting in 2018, the G20 brought an updated interior and exterior design. Two engines were offered depending on the trim level: the B48 and B58. The B48 is a turbocharged four-cylinder, while the B58 is a turbocharged inline-six.

3-Series B48 Common Problems

We lied about the B48 being used in the G20. Kind of. Technically, the US market gets a variant of the B48 called the B46. They are identical, other than a few small differences that allow the B46 to meet tighter emissions regulations. The power output between the two is the same. Rather than using two different engines in the same market (states like California have much higher emissions requirements), BMW opted to use the B46 across the US. We’ve covered B48 problems in the past since this engine is used in certain MINI Cooper models, but we will recap them here. While it’s important to note this difference, we will refer to this engine as the B48.

Valve Cover Leaks

The valve cover is a common failure point on the B48/B46 engine. The valve cover sits at the very top of the engine, protecting the camshafts and valvetrain while keeping oil contained in the motor while it’s running. The gaskets that seal the cover to the cylinder head can start to leak, leading to oil loss and contamination of the engine bay with oil. 

Luckily, the gasket is not expensive and the labor time involved with this repair is relatively low, given its location on top of the engine. 

Oil Filter Housing Leak

The oil filter on the B48 is located on top of the engine, and the housing connecting it to the engine block is prone to failure. Common symptoms include external oil leaks and oil leaking into the coolant system. The OEM housings are made of plastic and can crack around the gaskets, resulting in leaks. These failures have been seen as early as 60,000 miles.

Replacing the oil filter housing is an in-depth procedure that involves removing the intake manifold. Aluminum housings are available, which may provide longer durability than the original plastic housing.

Exhaust Gas Recirculation (EGR) Valve Issues

EGR valves redirect some exhaust gasses back through the intake side of the motor, allowing the harmful emissions to combust again, reducing the overall pollutant output of the motor.

In addition to failing emissions tests, a failed EGR valve can impact the way your engine runs. You may see reduced performance, smell gasoline, experience rough idle, and the engine can even stall. 

VANOS Solenoid Problems

VANOS is BMW’s name for its variable valve timing system. VANOS problems have plagued nearly every BMW engine equipped with them, and the B48 is no exception. Using oil pressure, the VANOS solenoid changes the valve timing of the motor, allowing for improved performance and efficiency under different driving conditions. Over time, the solenoids that actuate the camshafts can become clogged with oil and other debris, and the rubber seals inside can fail as well.

VANOS problems can present in several ways, including: 

  • Limp mode
  • Warning lights
  • Rough idle
  • Slow acceleration
  • Bad fuel economy
  • Slow cold starts
  • Rattling noise

Oil Consumption

Consuming oil is part of owning a BMW. From external leaks to oil burning, you may notice your oil level decrease between services. Using high-quality synthetic oil and performing frequent oil changes can help reduce the amount of oil your engine is consuming.

Staying aware of oil consumption problems is critical. If the engine is operating with insufficient lubrication, catastrophic (and expensive) damage can occur.

B58 Common Problems

The B58 is the big brother of the B48. With two more cylinders and a significantly higher power output, this motor is reserved for the performance-oriented 340i. Outside of the 3-Series, the B58 powers many other cars in BMW’s lineup including the 4-series, X3 M40i, X5, and even the new Toyota Supra. 

While the B58 is a significant improvement over the previous iterations of BMW’s turbocharged inline-six (read more about the N54 and N55 here), 340i owners still need to be on the lookout for a few things. 

Valve Cover Gasket

Like the B48, the B58 also suffers from leaking valve covers. The procedure to replace this gasket is the same as on the four-cylinder but can cost more since the gasket is larger and the labor times are higher. 

Coolant Consumption

Coolant loss on the B58 isn’t caused by one specific failure, but it’s common enough that you will see complaints about it on many forums dedicated to BMW Enthusiasts.

A few primary causes of coolant consumption have been identified, ranging from minor repairs to in-depth engine teardown.

  • Water Pump Failure
  • Coolant Reservoir Cap Leaking
  • Failed Turbocharger
  • Leaking Coolant Reservoir
  • Head Gasket Failure 

Oil Filter Disintegration

This issue is present on both the B48 and B58, and it can be a serious one. Over time, the oil filters in these cars can start to come apart, literally disintegrating and ripping in the car. Without a functioning oil filter, you run the risk of damaging the delicate rotating components in your engine. 

Staying on top of routine oil services and not going past the mileage limit can help prevent this issue from occurring. 

G80 M3 Common Problems

The code “G80” designates the M3, the high-performance variant of the 3-series. This vehicle differs in several ways from the G20 models. First off, the engine. The G80 is powered by the S58 engine, which is a high-output version of the B58. Besides having more power, the S58 utilizes a twin-turbo setup (as opposed to the B58’s single turbo). The S58 also has a lower compression ratio and utilizes forged internal components. Everything about the S58 is focused on performance. 

The differences don’t stop there, the G80, unlike the G20, can be optioned with a manual transmission or an 8-speed automatic. 

The G80 M3 is a relatively new vehicle, being introduced in 2019. Given their relative rarity compared to the B58, there is not a lot of information available at this time regarding pattern failures with the S55. 

BMW Service in Salt Lake City

Whether you drive a 330i with a B48 or a G80 M3 Competition with an S55, Alex’s Autohaus is your go-to dealership alternative for service, repair, and performance upgrades. Our technicians are experts in all things European, which means we know your BMW inside and out. Give us a call or schedule an appointment online today!

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