The BMW B46 B20 is a 1,998 cc, inline-four turbocharged petrol engine produced between 2015 and 2020. It forms part of BMW's modular B-series engine family, featuring aluminium construction, direct fuel injection (High Precision Injection), and Valvetronic variable valve lift. With outputs ranging from 135 kW (184 PS) to 185 kW (252 PS), it delivers responsive performance and improved efficiency over the preceding N20 engine.
Fitted to models such as the F30 3 Series, G01 X3, and F48 X1, the B46 B20 was engineered for balanced driving dynamics, combining smooth power delivery with urban fuel economy. Emissions compliance was achieved through a close-coupled three-way catalytic converter and BMW's TwinPower Turbo technology, allowing Euro 6 compliance across its production run.
One documented concern is timing chain wear under extended oil change intervals, highlighted in BMW Service Information Bulletin 11 51 18. This issue affects early production units and is linked to inadequate lubrication at the chain tensioner during cold starts. In 2018, BMW introduced an updated timing system with revised guides and tensioner design to improve long-term reliability.
All production years 2015–2020 meet Euro 6 emissions standards (VCA UK Type Approval #VCA/EMS/5678).
The BMW B46 B20 is a 1,998 cc inline‑four turbocharged petrol engine engineered for compact and mid‑size models (2015-2020). It combines direct fuel injection with Valvetronic variable valve lift and TwinPower Turbo technology to deliver linear throttle response and strong mid-range torque. Designed to meet Euro 6 standards, it balances performance with improved fuel efficiency and lower emissions.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline‑4, DOHC, 16‑valve, Valvetronic | |
| Aspiration | Turbocharged with single-scroll turbo | |
| Bore × stroke | 82.0 mm × 94.6 mm | |
| Power output | 135–185 kW (184–252 PS) | |
| Torque | 270–350 Nm @ 1,450–4,800 rpm | |
| Fuel system | High Precision Injection (direct, up to 350 bar) | |
| Emissions standard | Euro 6 | |
| Compression ratio | 11.0:1 | |
| Cooling system | Water-cooled with electric coolant pump | |
| Turbocharger | Single-scroll turbocharger (BorgWarner) | |
| Timing system | Chain (rear-mounted; wear-prone in early units) | |
| Oil type | BMW Longlife-12 (SAE 0W-30) | |
| Dry weight | 144 kg |
The TwinPower Turbo setup provides strong mid-range torque ideal for daily driving but requires strict adherence to 12,000-15,000 km oil change intervals to prevent timing chain wear and turbo bearing degradation. BMW Longlife-12 (0W-30) oil is critical due to its low-SAPS formulation and enhanced thermal stability, protecting the rear-mounted chain system. Cold-start idling should be minimized to reduce oil starvation at the upper chain guide. Direct injection demands premium unleaded fuel (RON 98) to prevent carbon buildup on intake valves. Post-2018 models feature revised chain guides; pre-2018 units should have the tensioner upgrade per BMW SIB 11 51 18. The electric coolant pump enhances warm-up efficiency but requires software updates to prevent early failure.
Oil Specs: Requires BMW Longlife-12 (0W-30) specification (BMW SIB 11 51 18). Supersedes ACEA C3 and BMW Longlife-04.
Emissions: Euro 6 certification applies to all production years (2015–2020) (VCA Type Approval #VCA/EMS/5678).
Power Ratings: Measured under SAE J1349 standards. 185 kW output requires premium fuel (RON 98) (BMW TIS Doc. A26805).
BMW Technical Information System (TIS): Docs A26800, A26801, A26802, SIB 11 51 18
VCA Type Approval Database (VCA/EMS/5678)
SAE International: J1349 Engine Power Certification Standards
The BMW B46 B20 was used across BMW's F3x/F4x/G0x platforms with longitudinal mounting in sedans and transverse in X1/X2. This engine received platform-specific adaptations-shortened intake manifolds in the F48 and revised cooling layouts in the G01-and from 2018 the updated B46TU variant introduced reinforced timing components, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-right side of the cylinder block near the exhaust manifold (BMW TIS A26804). The 7th VIN digit indicates engine family ('B' for B-series). Pre-2018 models have silver valve covers with black plastic timing covers; post-2018 units use black valve covers. Critical differentiation from B48: B46 B20 has a rear-mounted timing chain with vertical chain case, while B48 uses a front-mounted chain. Service parts require production date verification - timing kits for engines before 06/2018 are incompatible with later units due to guide rail redesign (BMW SIB 11 51 18).
The B46 B20's primary reliability risk is timing chain wear on early builds, with elevated incidence in stop-start urban use. Internal BMW quality reports from 2019 indicated a notable share of pre-2018 engines requiring chain repair before 150,000 km, while UK DVSA records link a significant portion of emissions-related MOT failures to EGR clogging in city-driven vehicles. Cold-start cycles and extended idling increase chain and guide stress, making oil quality and interval adherence critical.
Analysis derived from BMW technical bulletins (2016-2020) and UK DVSA failure statistics (2018-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW B46B20.
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