The problem
This BMW came to us with the N47 25d twin-turbo diesel engine. The customer said the car had no power and felt flat when accelerating.
We found the small turbo had failed. The main cause was a blocked turbo oil feed line.
How the twin-turbo N47 works
The 25d engine has two turbos. The small turbo works at low engine speed to give quick response. The big turbo takes over at higher speed.
When the small turbo fails, the car loses boost and feels very slow, especially when pulling away.
What went wrong
A turbo spins very fast and needs a steady supply of clean oil. Over time, old oil and heat can turn into hard carbon inside the oil feed line.
In this car, the oil line and turbo oil inlet were badly blocked with carbon. With no oil, the turbo bearings wore out. The shaft broke and the turbine wheel came apart.
Warning signs
- Lack of power or no boost
- The car goes into limp mode
- Engine warning light with boost faults
- Whistling or grinding noise from the turbo
- Smoke from the exhaust
- Oil in the intake pipes or intercooler
Which BMWs have this engine?
The twin-turbo N47 is found in models such as the 123d, 125d, 325d and X1 25d.
What we did
- Removed the turbo assembly
- Inspected the turbos and oil supply
- Replaced the failed small turbo
- Replaced the blocked turbo oil feed line
- Cleaned the intake pipes and checked the intercooler for oil and broken parts
- Changed the engine oil and filter
- Tested the car for full boost and power
Why replacing the oil line matters
If you fit a new turbo but keep the old blocked oil line, the new turbo can fail the same way. Always replace or clean the oil feed line when changing a turbo.
Prevention tips
- Change your oil on time, with the correct BMW-approved diesel oil
- Don’t stretch oil service intervals too far
- After hard driving, let the engine idle for 30–60 seconds before turning it off
- Get boost or power problems checked early
How we can help
At WA Auto Service Center in Bibra Lake, we specialise in BMW. If your BMW diesel has low power or turbo problems, book an inspection with us today.
