The Mitsubishi G64B is a 2,555 cc, inline‑six naturally aspirated petrol engine produced between 1986 and 1995. It features a single overhead camshaft (SOHC), 12 valves, and a carburettor or throttle-body fuel injection depending on market and year. In standard form it delivered 92–103 kW (125–140 PS) with torque figures between 192–210 Nm, offering smooth linear power delivery ideal for executive cruising.
Fitted to models such as the Debonair (A33A), Proudia (D-01), and Galant Σ (E39A), the G64B was engineered for quiet, vibration‑free operation with an emphasis on NVH refinement and drivetrain smoothness. Emissions compliance was achieved through basic closed‑loop fuel control and a three‑way catalytic converter, allowing compliance with pre‑Euro and early Euro 1 standards depending on model year and market.
One documented concern is premature wear of the distributor drive gear in carburetted variants, highlighted in Mitsubishi Technical Service Bulletin TSB‑ME‑87‑005. This issue was linked to marginal case hardening during initial high‑torque production runs. From 1990 onward, revised drive gears with improved metallurgy were introduced across the G64 family.
Production years 1986–1989 meet pre‑Euro standards; 1990–1995 models may comply with Euro 1 depending on market (JAMA Type Approval #JAMA/EMS/2031).
The Mitsubishi G64B is a 2,555 cc inline‑six naturally aspirated petrol engine engineered for executive sedans (1986–1995). It combines SOHC architecture with either carburettor or throttle-body injection to deliver smooth, vibration-free power. Designed to meet pre‑Euro and early Euro 1 standards, it prioritizes refinement over emissions sophistication.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,555 cc | |
| Fuel type | Petrol (Unleaded) | |
| Configuration | Inline‑6, SOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 85.0 mm × 75.0 mm | |
| Power output | 92–103 kW (125–140 PS) @ 5,000–5,500 rpm | |
| Torque | 192–210 Nm @ 3,500–4,000 rpm | |
| Fuel system | Carburettor or throttle-body injection (TBI) | |
| Emissions standard | Pre‑Euro (1986–1989); Euro 1 (1990–1995, market‑dependent) | |
| Compression ratio | 8.8:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain (maintenance‑free design) | |
| Oil type | API SF/SG, SAE 10W‑40 | |
| Dry weight | 158 kg |
The inline‑6 layout provides inherent balance and smooth operation but requires clean oil to protect the chain-driven valvetrain. Early carburetted variants (pre‑1990) are susceptible to distributor drive gear wear per TSB‑ME‑87‑005—symptoms include erratic ignition timing and misfires. Use of API SF/SG 10W‑40 oil is sufficient, but frequent oil changes every 7,500 km are recommended in hot climates. TBI units depend on functional oxygen sensors and clean throttle bodies for stable idle. Post‑1990 engines feature hardened drive gears and improved emissions control.
Oil Specs: Requires API SF or SG (SAE 10W‑40) specification (Mitsubishi Owner’s Manual). Modern SN oils are acceptable alternatives.
Emissions: Pre‑Euro certification applies to 1986–1989 models only (JAMA Type Approval #JAMA/EMS/2031). Euro 1 compliance was achieved in select 1990–1995 export variants.
Power Ratings: Measured under JIS D 1001 standards. Output varies by carburettor calibration and altitude compensation (Mitsubishi TIS Doc. ME‑G64B‑04).
Mitsubishi Technical Information System (TIS): Docs ME‑G64B‑01 to ME‑G64B‑04, TSB‑ME‑87‑005
JAMA Type Approval Database (JAMA/EMS/2031)
JIS D 1001: Road vehicles — Engine power test code
The Mitsubishi G64B was used across Mitsubishi's A33A/D-01 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced mounts in the Debonair and modified accessory brackets in the Proudia—and from 1990 the updated Galant Σ adopted throttle-body injection replacing carburettors, creating minor interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the left side of the cylinder block near the distributor (Mitsubishi TIS ME‑G64B‑07). The 7th VIN digit indicates engine family ('G' for G64x series). Early engines (1986–1989) have silver valve covers with external distributor; post‑1990 TBI units use black valve covers and integrated ignition modules. Critical differentiation from G63B: G64B has 2,555 cc displacement and unique intake manifold runner length. Distributor drive gear part numbers beginning with MD345xxx denote G64B applications. Service parts require production date verification—distributor gears for engines before 01/1990 are incompatible with later units due to metallurgy redesign (Mitsubishi TSB‑ME‑87‑005).
The G64B's primary reliability risk is distributor drive gear wear in early carburetted builds, with elevated incidence in high‑temperature or high‑load urban use. Mitsubishi internal quality reports from 1989 indicated a notable share of pre‑1990 engines requiring ignition system repair before 120,000 km, while JAMA durability audits flagged marginal drive train robustness in initial batches. Extended oil intervals and poor coolant maintenance accelerate timing chain and head gasket issues, making fluid service adherence critical.
Analysis derived from Mitsubishi technical bulletins (1987–1993) and JAMA failure statistics (1990–1998). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MITSUBISHI G64B.
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