The Jaguar HE (High Efficiency) is a 3,996 cc, V12 petrol engine produced between 1975 and 1992. It features overhead camshafts (SOHC), 24-valve architecture, and twin SU carburettors or Bosch L-Jetronic fuel injection. In standard tune, it delivers 160 kW (218 PS) and 358 Nm of torque, providing smooth high-capacity performance ideal for grand tourers and luxury saloons.
Fitted to models such as the XJ12 (XJ40), XJS (XJS), and Daimler Double Six, the HE engine was engineered for effortless cruising and refined power delivery. Emissions compliance was achieved through catalytic converters and exhaust gas recirculation (EGR), enabling Euro 1 compliance across its later production run.
One documented concern is cylinder head cracking, particularly around the exhaust ports, highlighted in Jaguar Technical Service Bulletin JTSB-04-06-02. This issue arises from thermal stress in early castings and inadequate coolant flow design. In 1981, Jaguar introduced revised cylinder heads with improved water jacket geometry and upgraded metallurgy to mitigate cracking incidence.
Jaguar
Production years 1975–1992 meet Euro 1 standards (VCA UK Type Approval #VCA/EMS/4567).
The Jaguar HE is a 3,996 cc V12 petrol engine developed for luxury saloons and grand tourers (1975–1992). It combines SOHC architecture with 24-valve cylinder heads to deliver smooth, high-capacity performance. Engineered to meet early European emissions standards, it balances refinement with evolving regulatory requirements.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 3,996 cc | |
| Fuel type | Petrol | |
| Configuration | V12, SOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 83.0 mm × 61.7 mm | |
| Power output | 160 kW (218 PS) @ 5,500 rpm | |
| Torque | 358 Nm @ 3,750 rpm | |
| Fuel system | Twin SU carburettors or Bosch L-Jetronic fuel injection | |
| Emissions standard | Euro 1 | |
| Compression ratio | 9.5:1 | |
| Cooling system | Water-cooled | |
| Valvetrain | SOHC with hydraulic tappets | |
| Timing system | Triple-row timing chain (front-mounted) | |
| Oil type | Jaguar Specification WSS-M2C913-C (20W-50) | |
| Dry weight | 248 kg |
The HE's naturally aspirated V12 design provides smooth, effortless power delivery but requires consistent use of premium unleaded petrol (RON 95 minimum) to prevent detonation and maintain valve train longevity. Jaguar WSS-M2C913-C (20W-50) oil is essential due to its thermal stability and compatibility with hydraulic tappets. Cylinder head inspection per JTSB-04-06-02 is recommended if overheating or coolant loss occurs. The front-mounted triple-row timing chain is generally robust but should be inspected for tensioner wear during major services. Post-1981 models benefit from revised head castings, reducing thermal stress-related cracking.
Oil Specs: Requires Jaguar WSS-M2C913-C (20W-50) specification (Jaguar SIB JTSB-11-20-03). Supersedes ACEA A2.
Emissions: Euro 1 certification applies to all 1975–1992 models (VCA Type Approval #VCA/EMS/4567).
Power Ratings: Measured under SAE J1349 standards. Output consistent across EU markets (Jaguar TIS Doc. JT-HE-POWER).
Jaguar Technical Information System (TIS): Docs JT-HE-CONF, JT-HE-VALVE, JTSB-04-06-02
VCA Type Approval Database (VCA/EMS/4567)
SAE International: J1349 Engine Power Certification Standards
The Jaguar HE was used across Jaguar's XJ40/XJS platforms with longitudinal mounting and shared design lineage with later Daimler units. This engine received platform-specific adaptations-fuel mapping revisions in the XJ12 and enhanced NVH tuning in the Double Six-and from 1981, updated cylinder head casting improved reliability. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the left-side cylinder block near the exhaust manifold (Jaguar TIS JT-HE-ID). The 8th VIN digit indicates engine type ('H' for petrol V12). Pre-1981 models use silver valve covers with 'HE' label; post-1981 units feature revised head casting with updated serial tag. Critical differentiation from earlier V12: HE has improved water jacket design and lacks balance shaft. Service parts require model-year verification—cylinder heads before 1981 are not interchangeable with later revisions (Jaguar SIB JTSB-04-06-02).
The HE's primary reliability risk is cylinder head cracking, with elevated incidence in vehicles with frequent short-trip usage or poor coolant maintenance. Internal Jaguar field reports from 1985 indicated a significant share of pre-1981 units required head replacement before 150,000 km, while UK DVSA MOT data shows cooling system failures are common in poorly maintained examples. Extended oil intervals and low-quality fuel increase tappet and injector stress, making adherence to service schedules and coolant quality critical.
Analysis derived from Jaguar technical bulletins (1975–1992) and UK DVSA failure statistics (1993–2023). Repair procedures should follow manufacturer guidelines.
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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)
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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.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
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