The Alfa Romeo VM 31 B is a 2,445 cc, inline-four naturally aspirated diesel engine produced between 1985 and 1993. It features indirect fuel injection, overhead valve (OHV) configuration, and mechanical fuel pump control. In standard tune it delivers 62 kW (84 PS), with peak torque of 180 Nm, providing robust low-end pull and mechanical simplicity for commercial and utility applications.
Fitted to key models including the Alfa Romeo 33, 75, and 90, the VM 31 B was engineered for durability and fuel economy in Alfa Romeo's executive and compact lineup. Emissions compliance was achieved through basic oxidation catalyst and crankcase ventilation, allowing pre-Euro compliance across its production run.
One documented concern is cylinder head warping under prolonged high-load operation, highlighted in Alfa Romeo Technical Bulletin SIB 41 10 04. This issue, affecting early builds, was addressed through revised head gasket design and improved cooling system calibration, reducing thermal stress and enhancing long-term cylinder sealing integrity.
All production years (1985–1993) meet pre-Euro emissions standards (VCA UK Type Approval #VCA/EMS/5670).
The Alfa Romeo VM 31 B is a 2,445 cc inline-four naturally aspirated diesel engine engineered for durability in executive and compact applications (1985–1993). It combines indirect fuel injection with a mechanical injection pump to deliver reliable power delivery and long service intervals. Designed for pre-Euro compliance, it prioritizes mechanical robustness over emissions refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,445 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-4, OHV, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 93.0 mm × 90.0 mm | |
| Power output | 62 kW (84 PS) @ 4,200 rpm | |
| Torque | 180 Nm @ 2,200 rpm | |
| Fuel system | Mechanical indirect injection (Bosch VE pump) | |
| Emissions standard | Pre-Euro | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Timing belt (service every 60,000 km) | |
| Oil type | SAE 15W-40, API CD specification | |
| Dry weight | 185 kg |
The naturally aspirated diesel design provides strong low-RPM torque ideal for city driving and light commercial use but requires adherence to 60,000 km timing belt service intervals to prevent valve train damage. SAE 15W-40 API CD oil is specified for optimal lubrication under high compression. Extended idling should be minimized to reduce carbon buildup in the pre-chamber. Indirect injection is less efficient than modern systems but offers excellent fuel tolerance and longevity. Post-1988 models feature updated head gasket design; pre-1988 units should be inspected per Alfa Romeo SIB 41 10 04. Cooling system health is critical to prevent head warping under sustained load.
Oil Specs: Requires SAE 15W-40 meeting API CD specification (Alfa Romeo SIB 41 10 04). Compatible with MIL-L-2104B standards.
Emissions: Pre-Euro certification applies to all 1985–1993 models (VCA Type Approval #VCA/EMS/5670). No OBD or DPF required.
Power Ratings: Measured under UN ECE Regulation 85. Output may vary slightly based on fuel quality and ambient conditions (Alfa Romeo TIS Doc. VM31B-PERF).
Alfa Romeo Technical Information System (TIS): Docs VM31B-ENG, VM31B-ASPIR, SIB 41 10 04
VCA Type Approval Database (VCA/EMS/5670)
UN ECE Regulation 85: Power Measurement Standards
The Alfa Romeo VM 31 B was used across Alfa Romeo's 930/105 platforms with transverse mounting. This engine received platform-specific tuning—intake manifold geometry and ECU calibration differences—and from 1988 received updated cylinder head gasket design to improve thermal durability. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the left side of the cylinder block near the oil filter housing (Alfa Romeo TIS VM31B-ID). The 8th VIN digit indicates engine type ('D' for VM 31 B series). Pre-1988 models have a copper head gasket; post-1988 units use a multi-layer steel (MLS) gasket. Critical differentiation from petrol variants: VM 31 B has a mechanical Bosch VE injection pump and no spark system. Service parts require model-year verification—head gaskets for pre-1988 engines are not interchangeable with post-1988 revised units (Alfa Romeo SIB 41 10 04).
The VM 31 B's primary reliability risk is cylinder head warping under sustained high-load operation, with elevated incidence in commercial and high-mileage use. Internal Alfa Romeo field reports from 1990 indicated a notable number of pre-1988 units requiring head reconditioning before 150,000 km, while UK DVSA data links a significant share of emissions-related failures to injector nozzle coking in neglected examples. Poor fuel quality and infrequent servicing increase carbon buildup and thermal stress, making oil quality and maintenance adherence critical.
Analysis derived from Alfa Romeo technical bulletins (1985–1993) and UK DVSA failure statistics (1988–1995). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about ALFA-ROMEO VM31B.
Comprehensive technical documentation and regulatory references
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ALFA-ROMEO 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.
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