M135i 3.0 Turbo (N55)
2012–2015 · petrol · 2979cc · 320hp
Engine codes: N55B30
Reliability, common problems and owner reviews for the Bmw 1 Series F20 M135i 3.0 Turbo (N55). Check this before you buy used.
The 320 hp N55 in the F20 M135i (2012–2015): the same single-turbo straight six as the 535i, with the same predictable items — electric water pump and thermostat, oil filter housing and valve cover gaskets, charge pipe and wastegate rattle. In a small hot hatch the extra risk is the owner: many are remapped and driven hard, so check for tuning, clutch/gearbox abuse and cooling history.
Known Issues
The N55's electric water pump fails with little warning (coolant warning, reduced power, overheating); the thermostat is usually replaced with it.
Fix / Workaround: Replace pump and thermostat together preventively around 110,000–150,000 km, or at the first coolant-temperature warning.
Repair cost: €700–€1200
Typically appears after: 110,000 km
The oil filter housing gasket leaks onto the auxiliary belt; an oil-soaked belt can be shredded and pulled behind the crank pulley into the front seal. The plastic valve cover (with integrated breather) cracks or its gasket leaks onto the exhaust.
Fix / Workaround: Replace the oil filter housing gasket early and check the belt; a cracked valve cover is replaced as an assembly.
Repair cost: €250–€800
Typically appears after: 100,000 km
Wastegate linkage rattle on cold start/overrun; the plastic charge pipe cracks (sudden loss of boost); injectors and the high-pressure pump can fail, though far less often than on the N54.
Fix / Workaround: Wastegate rattle is mostly noise; replace a cracked charge pipe with an aluminium one; injectors to the latest index only when they leak.
Repair cost: €200–€1200
Typically appears after: 120,000 km
Mileage Thresholds
After 110,000 km: Water pump/thermostat and oil filter housing gasket window.
Pre-Purchase Checklist
- ☐Scan for coolant-pump and thermostat faults
- ☐Look under the engine for oil at the filter housing and on the belt
- ☐Cold-start: wastegate rattle vs. chain/valvetrain noise
- ☐Signs of remapping (ECU read, exhaust, downpipe)
Frequently asked questions
Is the Bmw 1 Series F20 M135i 3.0 Turbo (N55) reliable?
Maint. Sensitive — The 320 hp N55 in the F20 M135i (2012–2015): the same single-turbo straight six as the 535i, with the same predictable items — electric water pump and thermostat, oil filter housing and valve cover gaskets, charge pipe and wastegate rattle. In a small hot hatch the extra risk is the owner: many are remapped and driven hard, so check for tuning, clutch/gearbox abuse and cooling history.
What are the common problems and reviews for the Bmw 1 Series F20 M135i 3.0 Turbo (N55)?
The most commonly reported problems: Electric water pump and thermostat, Oil filter housing and valve cover gaskets, Wastegate rattle, charge pipe and injectors.
Is a used Bmw 1 Series F20 M135i 3.0 Turbo (N55) worth buying?
Fine if serviced correctly — but it punishes neglect hard. History and the right consumables matter.