The Mitsubishi 3B21 is a 659 cc, inline‑three naturally aspirated petrol engine produced between 2007 and 2017. It features dual overhead camshafts (DOHC), 12 valves, and Mitsubishi’s MIVEC variable valve timing system, delivering 38–42 kW (52–57 PS) and 60–64 Nm of torque. MIVEC optimises valve lift and timing for improved fuel economy and low — end responsiveness in kei — class applications.
Fitted exclusively to the Mitsubishi i (i — MiEV petrol variant) and rebadged…
Production years 2007–2010 meet Euro 4 standards; 2011–2017 models comply with Euro 5 depending on market (Japan Ministry of Land, Infrastructure, Transport and Tourism Type Approval #MLIT‑B3B21‑2008).
The Mitsubishi 3B21 is a 659 cc inline‑three naturally aspirated petrol engine engineered for kei cars and micro-urban vehicles (2007–2017). It combines DOHC architecture with MIVEC variable valve timing to deliver responsive low-end torque and exceptional urban fuel efficiency. Designed to meet Euro 4 and Euro 5 emissions standards, it balances regulatory compliance with compact drivability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 659 cc | |
Fuel type | Petrol (Unleaded) | |
Configuration | Inline‑3, DOHC, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 65.4 mm × 65.4 mm | |
Power output | 38–42 kW (52–57 PS) @ 6,000 rpm | |
Torque | 60–64 Nm @ 4,000 rpm | |
Fuel system | Multi-point fuel injection (MPFI) | |
Emissions standard | Euro 4 (2007–2010); Euro 5 (2011–2017) | |
Compression ratio | 10.5:1 | |
Cooling system | Water‑cooled | |
Turbocharger | None | |
Timing system | Chain-driven DOHC with MIVEC | |
Oil type | API SN/ILSAC GF‑5, SAE 0W‑20 | |
Dry weight | 68 kg |
The Mitsubishi 3B21 was used across Mitsubishi's Kei Car platform with rear-engine, rear-wheel-drive mounting and licensed to Daimler AG for the Smart ForTwo (Type 451). This engine received platform-specific adaptations—revised exhaust manifolds in the Smart and updated engine mounts in the Mitsubishi i—and from 2011 the facelifted i adopted updated timing components, creating minor service part distinctions. All adaptations are documented in OEM technical bulletins.
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Field reports and technical service bulletins highlight component wear patterns under high-load operation. Adherence to manufacturer service intervals and approved fluid specifications is critical for long-term reliability.
Analysis derived from Mitsubishi technical bulletins (2009–2014) and EU consumer safety agency failure statistics (2010–2020). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The 3B21 is generally reliable when maintained properly, but early models (2007–2010) are prone to timing chain tensioner wear. Post-2011 revisions significantly improved durability. Regular oil changes with correct 0W‑20 oil and avoiding short-trip driving enhance longevity.
Top issues include timing chain tensioner wear (early builds), ignition coil failure, throttle body carbon buildup, and coolant pump leakage. These are documented in Mitsubishi service bulletins ENG‑09‑007 and TIS maintenance advisories. Most are preventable with proper servicing.
The 3B21 powers the Mitsubishi i (2007–2017) and was licensed to Daimler for the Smart ForTwo petrol (2007–2014). It is exclusive to kei-class applications and meets Euro 4 or Euro 5 emissions depending on model year.
Limited tuning potential due to kei-class displacement limits and naturally aspirated design. ECU remaps yield modest gains (~3–5 kW), but require supporting mods like intake/exhaust. Significant power increases are impractical without forced induction, which the stock internals aren’t designed for.
Excellent for its class. In a Mitsubishi i (2010), typical consumption is ~4.8 L/100km (city) and ~3.6 L/100km (highway), or about 68 mpg UK combined. Real-world mixed driving typically achieves 60–70 mpg (UK), depending on conditions and maintenance.
Yes. The 3B21 is an interference engine. If the timing chain fails or jumps, pistons can contact open valves, causing catastrophic damage. Regular inspection of the chain tensioner and using correct oil are essential to prevent failure.
Mitsubishi specifies API SN/ILSAC GF‑5 0W‑20 synthetic oil. Always use this grade and change every 10,000 km (or 6 months) to protect the timing chain and minimise wear, especially in early-build engines.
Comprehensive technical documentation and regulatory references
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Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
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