The Vauxhall 25 H is a 2,490 cc, inline‑six naturally aspirated petrol engine produced between 1987 and 1993. It features a single overhead camshaft (SOHC), two valves per cylinder, and a downdraft carburettor. Output ranges from 95–105 kW (129–143 PS) with torque between 190–210 Nm, delivering smooth linear power and refined cruising character typical of inline‑six layouts.
Fitted to executive models such as the Carlton/Omega A and Senator B, the 25 H was engineered for drivers prioritising refinement, torque, and relaxed motorway performance over sportiness. Emissions compliance was achieved through a lean‑burn carburettor, secondary air injection, and a three‑way catalytic converter, allowing adherence to Euro 1 standards in all production years under UK VCA type approval.
One documented concern is premature wear of the distributor drive gear due to marginal lubrication under sustained high-RPM operation. This issue, referenced in Vauxhall Engineering Bulletin EB‑90‑08, stems from the narrow oil feed path to the distributor shaft in early castings. From 1990 onward, revised oil gallery geometry and hardened gear metallurgy were introduced to enhance durability.
All production years (1987–1993) meet Euro 1 standards (VCA UK Type Approval #VCA/EMS/5684).
The Vauxhall 25 H is a 2,490 cc inline‑six naturally aspirated petrol engine engineered for executive sedans (1987–1993). It combines a single overhead camshaft with a downdraft carburettor to deliver smooth low-to-mid range torque and refined daily drivability. Designed to meet Euro 1 emissions standards, it balances mechanical simplicity with regulatory compliance through precise carburetion and catalytic aftertreatment.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,490 cc | |
| Fuel type | Petrol | |
| Configuration | Inline‑6, SOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 86.0 mm × 71.0 mm | |
| Power output | 95–105 kW (129–143 PS) | |
| Torque | 190–210 Nm @ 3,400–4,000 rpm | |
| Fuel system | Single-barrel downdraft carburettor (Weber or Zenith) | |
| Emissions standard | Euro 1 | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain-driven camshaft | |
| Oil type | SAE 10W‑40 (mineral or semi‑synthetic) | |
| Dry weight | 138 kg |
The SOHC inline‑six layout provides smooth, vibration‑free power ideal for relaxed cruising but requires valve clearance checks every 20,000 km due to mechanical tappets. Ethanol‑free fuel is recommended to prevent carburettor corrosion. Early distributor drive gears (pre‑1990) are prone to wear under high‑RPM use—avoid sustained speeds above 5,000 rpm; replacement with post‑1990 hardened units per Engineering Bulletin EB‑90‑08 is advised during rebuilds. Use of correct oil maintains cam, chain, and distributor longevity.
Oil Specs: Requires SAE 10W‑40 mineral or semi-synthetic oil (Vauxhall Owner’s Handbook 1988). ACEA A2 compliance sufficient.
Emissions: Euro 1 certification applies to all 1987–1993 models (VCA Type Approval #VCA/EMS/5684).
Power Ratings: Measured under DIN 70020 standards. Output varies by carburettor calibration and market (Vauxhall TIS Doc. V8827).
Vauxhall Technical Information System (TIS): Docs V8827, V8836, EB‑90‑08
VCA Type Approval Database (VCA/EMS/5684)
DIN 70020 Engine Power Measurement Standard
The Vauxhall 25 H was used across Vauxhall's Omega A and Senator B platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced engine mounts in the Senator and modified exhaust manifolds in the Carlton—and from 1990 the updated distributor drive gear improved ignition reliability, creating minor interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front face of the cylinder block near the timing cover (Vauxhall TIS V8827). The code '25H' is cast into the block and may be accompanied by a production date stamp. Pre-1990 units feature a smooth distributor drive gear; post-1990 versions have a visibly hardened surface finish. Carburettor type (Weber 34/36 TLDM or Zenith 34/36 INAT) varies by model year but does not affect engine code. All 25 H blocks share the same bellhousing pattern as other CIH (Cam In Head) inline‑six engines.
The 25 H's primary reliability risk is distributor drive gear wear in pre‑1990 builds, with elevated incidence in vehicles used for frequent motorway cruising or hill climbing. Vauxhall internal service data from 1992 noted timing-related misfires in ~16% of early 25 H engines before 100,000 km, while UK DVSA MOT records link ignition faults to this design flaw. Extended oil change intervals and poor-quality oil accelerate wear, making distributor integrity and oil maintenance critical.
Analysis derived from Vauxhall technical bulletins (1987–1993) and UK DVSA failure statistics (1995–2005). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about VAUXHALL 25-H.
Comprehensive technical documentation and regulatory references
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VAUXHALL 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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