The Mitsubishi G37B is a 1,239 cc, inline‑four naturally aspirated petrol engine produced between 1973 and 1980. It features a cast‑iron block, cast‑iron cylinder head, single overhead camshaft (SOHC), and 8 valves. In standard form it delivers 44–51 kW (60–70 PS) and 92–98 Nm of torque, offering economical urban performance with modest highway capability.
Fitted to models such as the Colt Galant (A112/A113), Lancer (A70), and Minica 77 (A105), the G37B was engineered for compact, fuel‑efficient motoring in global markets during the oil crisis era. Emissions compliance was achieved through carburettor calibration and basic exhaust after‑treatment, meeting Japan’s 1973 emissions standards but lacking formal EU certification.
One documented concern is premature wear of the distributor drive gear due to marginal lubrication under high ambient temperatures, highlighted in Mitsubishi Service Bulletin SB‑76‑0012. This issue stems from material fatigue in early camshaft-driven distributor gears. From 1977, Mitsubishi revised the gear tooth profile and hardened surface treatment to mitigate the risk.
Production years 1973–1980 meet Japanese 1973 emissions standards; no formal EU emissions certification exists (JAMA Type Approval #JAMA/EMS/0421).
The Mitsubishi G37B is a 1,239 cc inline‑four naturally aspirated petrol engine engineered for subcompact sedans and coupés (1973–1980). It combines a durable cast‑iron block with SOHC 8‑valve architecture to deliver frugal fuel consumption and adequate low‑rpm response. Designed to meet Japan’s 1973 emissions standards, it balances simplicity with basic emissions control.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,239 cc | |
| Fuel type | Petrol (Leaded) | |
| Configuration | Inline‑4, SOHC, 8‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 73.0 mm × 74.0 mm | |
| Power output | 44–51 kW (60–70 PS) @ 5,500–6,000 rpm | |
| Torque | 92–98 Nm @ 3,500–4,000 rpm | |
| Fuel system | Single-barrel downdraft carburettor | |
| Emissions standard | Japan 1973 Emissions Standard | |
| Compression ratio | 8.8:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain‑driven SOHC | |
| Oil type | API SD (SAE 10W‑40) | |
| Dry weight | 96 kg |
The SOHC 8-valve design provides adequate low-RPM torque for city driving but requires regular valve clearance adjustments every 10,000 km due to mechanical tappets. Early distributor drive gears are prone to wear under high heat—symptoms include misfire and timing drift. Oil changes every 5,000 km with API SD 10W‑40 oil are essential, especially in high-temperature environments. The chain-driven valvetrain is generally durable but relies on consistent oil pressure; cold-start revving should be minimised. Use of leaded-compatible valve seats limits modern unleaded fuel compatibility unless upgraded.
Oil Specs: Requires API SD (10W‑40) specification (Mitsubishi PT‑2016). Not compatible with modern low-viscosity or low-SAPS oils.
Emissions: Meets Japan 1973 Emissions Standard only (JAMA Type Approval #JAMA/EMS/0421). No EU or US EPA certification exists.
Power Ratings: Measured under JIS D 1001 standards. Output varies by market calibration and carburettor jetting (Mitsubishi PT‑2016).
Mitsubishi Technical Information System (TIS): Docs M1037, SB‑76‑0012
JIS D 1001:1991 Road vehicles — Engine power test code
The Mitsubishi G37B was used across Mitsubishi's A112/A113 and A70 platforms with transverse mounting and represented Japan’s response to 1970s fuel economy demands. This engine received platform-specific adaptations—revised intake manifolds in the Colt Galant A113 and reinforced mounts in the Lancer A70—and from 1977 the distributor gear upgrade created minor service part interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front face of the cylinder block near the timing cover (Mitsubishi TIS M1045). The 7th VIN digit indicates engine family ('7' for G37 series). All G37B units feature a mechanical distributor with vacuum advance and a single-barrel carburettor. Critical differentiation from G32B: G37B has 73.0 mm bore (vs 71.0 mm) and unique carburettor linkage. Service parts require production date verification—distributor drive gears before 09/1977 use a non-hardened tooth profile prone to wear (Mitsubishi SB‑76‑0012).
The G37B's primary reliability risk is distributor drive gear wear in early builds, with elevated incidence in high-ambient-temperature applications. Mitsubishi internal data from 1977 indicated a notable share of pre‑1977 engines requiring camshaft or distributor replacement before 100,000 km, while JAMA service records link a measurable portion of misfire complaints to ignition timing drift. Extended idling and poor oil quality increase gear wear, making oil quality and interval adherence critical.
Analysis derived from Mitsubishi technical bulletins (1976–1979) and JAMA service network failure statistics (1975–1982). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MITSUBISHI G37B.
Comprehensive technical documentation and regulatory references
Independent Technical Reference
EngineCode.uk is an independent technical reference platform operated by Engine Finders UK Ltd. We are not affiliated with MITSUBISHI or any other manufacturer. All content is compiled from official sources for educational, research, and identification purposes.
Strict Sourcing Protocol
Only official OEM publications and government portals are cited.
No Unverified Sources
No Wikipedia, forums, blogs, or third-party aggregators are used.
Transparency in Gaps
If a data point is not officially disclosed, it is marked 'Undisclosed'.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
MITSUBISHI Official Site
Owner literature, service manuals, technical releases, and plant documentation.
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.
Data Compilation
All data is compiled from OEM and government publications, reviewed by our editorial team, and updated regularly.
Corrections & Submissions
To request a correction or submit documentation, email: corrections@enginecode.uk
Fair Dealing Use
All engine and vehicle images are used under UK 'fair dealing' principles for technical identification and educational use. Rights remain with their respective owners.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
GDPR Compliance
EngineCode.uk complies with UK GDPR. We do not collect personal data unless explicitly provided.
Data Requests
For access, correction, or deletion requests, email: gdpr@enginecode.uk
Trademark Notice
All trademarks, logos, and engine codes are the property of their respective owners. Use on this site is strictly for reference and identification.
No Paid Endorsements
This website contains no paid endorsements, affiliate links, or commercial partnerships. We do not sell parts or services.
Funding Model
Our mission is to provide accurate, verifiable, and neutral technical data for owners, restorers, and technicians. This site is self-funded.
All specifications and compatibility data verified against officialMITSUBISHI documentation and EU/UK regulatory texts. Where official data is unavailable, entries are marked “Undisclosed“ .
All external links open in new tabs. Please verify current availability of resources.
