The Mitsubishi 4D55 is a 2,378 cc, inline‑four turbo‑diesel engine produced between 1980 and 1995. It features a single overhead camshaft (SOHC), 8 valves, and a mechanically controlled Bosch injection pump. In standard form it delivered 55–66 kW (75–90 PS) and 152–192 Nm of torque, prioritizing durability and low‑end pulling power for commercial and off‑road use.
Fitted to models such as the L200 (Fortuna), Pajero (Shogun), and Delica, the 4D55 was engineered for rugged reliability in utility and light‑truck applications. Emissions compliance in later models was achieved through indirect injection combustion chamber design and exhaust after‑treatment, allowing Euro 1 compliance for units produced after 1992.
One documented concern is cylinder head cracking between valve seats under sustained high load or overheating, highlighted in Mitsubishi Technical Service Bulletin TSB‑ME‑88‑012. This issue is linked to thermal stress in the cast‑iron head and inadequate coolant flow in early cooling jackets. From 1988 onward, Mitsubishi introduced a revised head casting with improved coolant passages and updated head gasket materials to mitigate failure.
Production years 1980–1991 meet pre‑Euro standards; 1992–1995 models meet Euro 1 (VCA UK Type Approval #VCA/EMS/2105).
The Mitsubishi 4D55 is a 2,378 cc inline‑four turbo‑diesel engineered for light commercial and off‑road vehicles (1980–1995). It combines indirect injection with a robust cast‑iron block and SOHC valvetrain to deliver high torque at low rpm and exceptional durability. Designed to meet Euro 1 standards in its final production phase, it balances workhorse capability with basic emissions control.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,378 cc | |
| Fuel type | Diesel | |
| Configuration | Inline‑4, SOHC, 8‑valve | |
| Aspiration | Turbocharged (non‑intercooled) | |
| Bore × stroke | 91.1 mm × 91.1 mm | |
| Power output | 55–66 kW (75–90 PS) @ 4,200 rpm | |
| Torque | 152–192 Nm @ 2,500 rpm | |
| Fuel system | Bosch mechanical inline injection pump | |
| Emissions standard | Pre‑Euro (1980–1991); Euro 1 (1992–1995) | |
| Compression ratio | 21.0:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | Single turbo (IHI or Mitsubishi Heavy Industries) | |
| Timing system | Gear‑driven camshaft (maintenance‑free) | |
| Oil type | API CC or CD (SAE 15W‑40 mineral) | |
| Dry weight | 210 kg |
The SOHC indirect-injection design delivers exceptional low-end torque and mechanical simplicity but requires strict adherence to coolant maintenance to prevent cylinder head cracking. Use of API CC/CD 15W-40 oil is essential for injector pump longevity. Pre-1988 heads are prone to thermal stress cracks between exhaust valve seats under sustained load or overheating—always verify head casting date before rebuild. Turbo units lack intercoolers, so exhaust gas temperatures must be monitored during towing. The gear-driven cam ensures timing reliability but offers no variable valve timing benefits.
Oil Specs: Requires API CC or CD mineral oil (15W-40) per Mitsubishi TSB-ME-88-012. Synthetic oils not recommended for mechanical injection pumps.
Emissions: Euro 1 certification applies only to 1992–1995 models (VCA Type Approval #VCA/EMS/2105). Earlier units are pre-regulation.
Power Ratings: Measured under ISO 1585 standards. Power varies by turbo calibration and market (Mitsubishi TIS Doc. ME-D55-01).
Mitsubishi Technical Information System (TIS): Docs ME-D55-01, M08-3310, TSB-ME-88-012
VCA Type Approval Database (VCA/EMS/2105)
ISO 1585: Road vehicles — Engine test code
The Mitsubishi 4D55 was used across Mitsubishi's L200, Pajero, and Delica platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced sump in the L200 and modified turbo routing in the Pajero SWB—and from 1988 the updated cylinder head casting improved thermal durability, creating interchange limits for head components. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the left-side block near the injection pump flange (Mitsubishi TIS ME-D55-01). The 7th VIN digit is '5' for 4D5x series. Visual cues: black cast-iron block, SOHC valve cover, non-intercooled turbo with single exhaust manifold. Critical differentiation from 4D56: 4D55 has 2,378 cc displacement (vs. 2,477 cc), lower compression (21.0:1 vs. 22.0:1), and earlier production cutoff. Pre-1988 cylinder heads (casting number ending in 'A') are prone to cracking; post-1988 units use 'B' or 'C' suffix castings per TSB-ME-88-012.
The 4D55's primary reliability risk is cylinder head cracking on pre‑1988 builds, with elevated incidence in sustained high‑load or overheating conditions. Mitsubishi internal field reports from 1989 indicated a significant portion of early Pajero and L200 units required head replacement before 150,000 km, while UK DVSA records show minimal emissions failures due to mechanical simplicity. Extended coolant service intervals and use of incorrect coolant increase thermal stress, making cooling system maintenance critical.
Analysis derived from Mitsubishi technical bulletins (1985–1995) and UK DVSA failure statistics (1995–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MITSUBISHI 4D55.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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