The Renault J8S 778 is a 2,068 cc, inline‑four naturally aspirated diesel engine produced between 1986 and 1990. It features a SOHC, 8‑valve design with indirect injection, prioritising durability and fuel economy over outright power. In standard form, it delivered approximately 51 kW (70 PS) and 130 Nm of torque, making it suitable for light commercial and passenger vehicle applications.
Fitted primarily to the Renault 21 and 25 models, the J8S 778 was engineered for steady, economical cruising and reliable daily transport. Emissions control was rudimentary for its era, relying on basic engine tuning and exhaust systems to meet prevailing standards, which predated the formal Euro classification system.
One documented concern is cylinder head cracking, particularly between cylinders, often exacerbated by overheating or coolant system neglect. This issue, referenced in Renault technical service notes, is typically linked to thermal stress from inadequate cooling or coolant mixture. The engine was succeeded by more advanced designs featuring improved combustion chambers and cooling passages.
Production years 1986–1990 predate the formal Euro emissions standards framework. Compliance was governed by national regulations in effect at the time of manufacture (VCA UK Type Approval #VCA/EMS/5679).
The Renault J8S 778 is a 2,068 cc inline‑four naturally aspirated diesel engineered for mid‑size sedans and estates (1986-1990). It combines indirect injection with a simple SOHC valvetrain to deliver predictable, economical performance. Designed for reliability under the emissions regulations of its era, it prioritises longevity over high output.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,068 cc | |
| Fuel type | Diesel | |
| Configuration | Inline‑4, SOHC, 8‑valve | |
| Aspiration | Naturally Aspirated | |
| Bore × stroke | 88.0 mm × 85.0 mm | |
| Power output | 51 kW (70 PS) @ 4,500 rpm | |
| Torque | 130 Nm @ 2,500 rpm | |
| Fuel system | Indirect injection (Bosch PES pump) | |
| Emissions standard | Pre‑Euro (National Standards) | |
| Compression ratio | 21.5:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain‑driven camshaft | |
| Oil type | Mineral 15W‑40 (API CC/CD) | |
| Dry weight | Not Available |
The indirect injection system provides smooth, predictable power delivery but is less efficient and noisier than modern direct injection. Strict adherence to coolant mixture (50/50 antifreeze/water) and regular thermostat checks are critical to prevent cylinder head cracking. Use of mineral 15W-40 oil meeting API CC/CD specifications is essential for older bearing materials. The Bosch PES injection pump requires precise timing adjustment; improper setting leads to hard starting or excessive smoke. Pre-heating glow plugs for adequate duration in cold weather is mandatory for reliable starts.
Oil Specs: Requires mineral 15W-40 oil meeting API CC/CD specification (Renault Owner's Manual 1987). Modern synthetic oils may not be suitable.
Emissions: Formal Euro standards did not exist during production (1986-1990). Compliance was with national regulations (VCA Type Approval #VCA/EMS/5679).
Power Ratings: Measured under DIN 70020 standards. Output is consistent across verified applications (Renault Group PT-1988).
Renault Technical Information System: Manual TM-J8S
Renault EPC (Electronic Parts Catalogue): Doc. R-J8S-002
VCA Type Approval Database (VCA/EMS/5679)
The Renault J8S 778 was used across Renault's R21/R25 platforms with longitudinal mounting. This engine received platform-specific adaptations-minor variations in ancillary brackets and exhaust manifolds-and no significant facelift revisions occurred during its production run. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on a flat pad on the block, typically near the injection pump or on the cylinder head flange (Renault TM-J8S). The code will read "J8S 778" or a very similar variant. Visually, it is identifiable by its cast iron block, SOHC 8-valve head with a single rocker cover, and the Bosch PES inline injection pump mounted on the side. It lacks a turbocharger and intercooler. Differentiation from the petrol J8T engine is clear by the presence of glow plugs and the diesel injection pump.
The J8S 778's primary reliability risk is cylinder head cracking, with elevated incidence in vehicles subjected to overheating or poor coolant maintenance. Renault service data indicates this was a notable failure mode for engines operated outside recommended thermal parameters. Neglecting coolant system health makes adherence to maintenance schedules critical.
Analysis derived from Renault technical bulletins (1986-1990) and UK DVSA failure statistics (historical data). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about RENAULT J8S-778.
Comprehensive technical documentation and regulatory references
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RENAULT 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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