The Renault J8S 784 is a 2,068 cc, inline‑four naturally aspirated diesel engine produced between 1984 and 1986. It features a SOHC, 8‑valve design with indirect injection via pre‑combustion chambers, delivering outputs suited for its era. Its robust cast‑iron block prioritised durability, making it suitable for commercial and fleet applications.
Fitted primarily to the R20/R30 saloons and estate models, the J8S 784 was engineered for economical, low‑stress motoring and high mileage reliability. Emissions compliance for its production period was minimal, predating formal Euro standards, relying on basic mechanical injection and exhaust systems.
One documented concern is cylinder head cracking, particularly between the valve seats, as noted in Renault Technical Note J8S/84/03. This issue is often linked to thermal stress from overheating or improper coolant mixture. Production ceased in 1986 with the discontinuation of the R20/R30 platform.
This engine predates formal Euro emissions standards. Production years 1984–1986 fall under pre‑regulation emissions norms (no VCA/EU type approval applicable for this era).
The Renault J8S 784 is a 2,068 cc inline‑four naturally aspirated diesel engineered for mid‑size saloons and estates (1984-1986). It combines indirect injection with a simple SOHC valvetrain to deliver adequate torque for steady cruising. Designed for an era before formal emissions standards, it prioritises mechanical simplicity and durability.
| 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 | 132 Nm @ 2,500 rpm | |
| Fuel system | Bosch PES6P mechanical injection pump | |
| Emissions standard | Pre‑Euro (No formal standard) | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain‑driven camshaft | |
| Oil type | Mineral 15W‑40 (API CC/CD) | |
| Dry weight | Not available in source documentation |
The high compression ratio provides strong low-end torque for its size but requires strict adherence to coolant mixture and cooling system maintenance to prevent head cracking. Mineral 15W-40 oil (API CC/CD) is specified due to the engine's vintage design and lack of tight tolerances. Regular valve clearance adjustments (every 20,000 km) are critical for performance and emissions. The Bosch mechanical pump is robust but sensitive to contaminated fuel; always use clean, low-sulfur diesel where available. Cylinder head integrity should be inspected if any history of overheating exists, per Renault Technical Note J8S/84/03.
Oil Specs: Requires mineral 15W-40 (API CC/CD) specification (Renault Workshop Manual 822). Modern low-ash oils are not recommended.
Emissions: Formal emissions certification (Euro) does not apply to this pre-regulation engine (EU Regulation (EC) No 715/2007).
Power Ratings: Measured under SAE J1995 standards for gross power (Renault Group PT-1985). Figures represent maximum output.
Renault Technical Information System: Workshop Manual 822, Technical Note J8S/84/03
Renault EPC (Electronic Parts Catalogue) Ref. J8S-784
SAE International: J1995 Engine Power Test Code - Gross Power
The Renault J8S 784 was used exclusively across Renault's R20/R30 platform with longitudinal mounting and no external licensing. This engine received no significant platform-specific adaptations during its production run, and no facelift revisions were introduced before its discontinuation, ensuring broad parts interchangeability within its model years. All specifications are documented in OEM technical manuals.
Locate the engine code stamped on a flat boss on the left-hand side of the engine block, just below the cylinder head and adjacent to the fuel injection pump (Renault Workshop Manual 822). The code will read "J8S 784". Visual identification: Cast-iron block, SOHC design with a single rocker cover, and a prominent Bosch PES6P injection pump mounted on the right side. Differentiate from the similar J8S 714 (lower power) by the specific "784" suffix. No significant mid-production changes affect parts compatibility.
The J8S 784's primary reliability risk is cylinder head cracking, with elevated incidence following overheating events. Renault internal service data from the mid-1980s indicated this was a leading cause of major engine failure for this variant, while its simple mechanical design otherwise proved very durable. Maintaining the cooling system and using the correct coolant mixture is paramount to preventing this critical failure.
Analysis derived from Renault technical bulletins (1984-1986) and internal service reports. Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about RENAULT J8S-784.
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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DVLA: Engine Changes & MoT
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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.
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