Disclaimer:
This post is based on my personal experience and intended for informational and educational purposes only. Procedures, tools, and parts may vary depending on the vehicle and situation. Always consult your service manual or a professional before performing any maintenance.For more information, please read the full disclaimer here.
BMW 420d B47 Engine – Replacing the Crankcase Breather Hose
While performing a routine visual inspection on my BMW F36 Gran Coupe (420d), I noticed something concerning — a slight oily residue around the crankcase breather hose. It wasn’t leaking heavily, but the area was clearly darker and greasy, suggesting there was a problem. Upon closer inspection, I discovered that the breather pipe was damaged and had developed a small crack.
Part number for this pipe in my case: 13-71-8-584-829
B47 Engine Visual Inspection – Damaged Crankcase Breather Hose
Below you can see photos of the damaged crankcase breather hose I removed from my BMW F36 420d. The crack is clearly visible, along with traces of oil leakage around the connection point. This kind of damage can easily go unnoticed, but over time it can lead to more serious issues like increased crankcase pressure and oil leaks.
Even though the breather hose was visibly damaged and leaking a bit of oil, there were no errors on the trip computer or fault codes during diagnostic checks.
Why This Breather Hose Is Important
Notice: This section was generated with the help of AI 🙂
The crankcase breather hose plays a crucial role in your engine’s ventilation system. It routes blow-by gases — unburnt fuel and oil vapors — from the crankcase back into the intake manifold so they can be burned off instead of venting into the atmosphere. This not only reduces emissions but also helps maintain optimal engine pressure.
Moreover, in my specific case, the hose includes a heating element, which is critical in cold weather. The built-in heater prevents moisture and oil vapors from freezing inside the hose. If the hose gets clogged due to freezing, it can lead to excessive crankcase pressure, oil leaks, and even severe engine damage over time.
Why This Breather Hose Is Important
Notice: This section was generated with the help of AI 🙂
Driving with a damaged breather hose may seem harmless at first, but it can quickly lead to more serious problems. Here’s what you risk:
- Oil Leaks: Pressure can force oil out of seals and gaskets.
- Rough Idle and Poor Performance: Unregulated airflow can affect the air-fuel mixture.
- Increased Emissions: Faulty ventilation leads to higher pollutant output.
- Winter Troubles: Without a working heating element, condensation can freeze and block the hose.
Simply put, ignoring this issue could result in higher maintenance costs later and poor driving experience, especially during colder months.
Why I Chose the Original Part
Given the heat levels in this area and the specific design of the hose — especially with the integrated heating element — I strongly believe that using anything other than the original part (Part No. 13-71-8-584-829) is not a good idea.
Aftermarket alternatives may lack the proper fit, material quality, or the heating feature, which is essential for long-term reliability in various climates.
Cost for this pipe was around 80 EUR.
Final Thoughts
If you notice oil residue near the crankcase breather on your BMW F36, don’t ignore it. A small crack can quickly lead to bigger problems. Replacing the hose is a relatively easy and affordable fix — and it can save you a lot of trouble down the road.
Have you dealt with a similar issue on your BMW? Let me know in the comments — I’d love to hear your experience!
In upcoming blog posts, I’ll be sharing practical examples of the functions I use most. Stay tuned if you want real-world insights into how this tool performs
