The Vauxhall 25 S is a 2,490 cc, inline‑six naturally aspirated petrol engine produced between 1978 and 1986. It features an overhead valve (OHV) layout with a single downdraft carburettor and cast‑iron block construction. In standard tune it delivered 100 bhp (75 kW) at 4,600 rpm and 145 lb·ft (197 Nm) of torque at 2,400 rpm, providing smooth, relaxed performance ideal for executive sedans and estates.
Fitted to models such as the Carlton Mk1, Viceroy, and Senator A, the 25…
Production years 1978–1982 meet pre‑Euro emissions norms; 1983–1986 models may include minor durability updates but remain Euro 0 compliant (VCA UK Type Approval #VCA/EMS/6487).
The Vauxhall 25 S is a 2,490 cc inline‑six OHV petrol engine engineered for executive sedans and estates (1978–1986). It combines a single carburettor with robust cast‑iron construction to deliver smooth power delivery and strong low‑rpm torque. Designed before formal EU emissions standards, it prioritizes drivability and serviceability over emissions control.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,490 cc | |
Fuel type | Petrol (unleaded post‑1979 with hardened valve seats) | |
Configuration | Inline‑6, OHV, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 88.9 mm × 100.0 mm | |
Power output | 100 bhp (75 kW) @ 4,600 rpm | |
Torque | 145 lb·ft (197 Nm) @ 2,400 rpm | |
Fuel system | Single downdraft carburettor (Zenith/Stromberg) | |
Emissions standard | Pre‑Euro / Euro 0 (no formal standard) | |
Compression ratio | 8.0:1 | |
Cooling system | Water‑cooled | |
Turbocharger | None | |
Timing system | Chain‑driven camshaft (front mounted) | |
Oil type | SAE 20W‑50 mineral oil (API SC/CC) | |
Dry weight | 165 kg |
The Vauxhall 25 S was used across Vauxhall's executive and large family car platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced mounts in the Senator and revised cooling ducts in the Viceroy—and from 1983 the introduction of multi‑layer steel head gaskets, creating service part compatibility limits. All adaptations are documented in OEM technical bulletins.
The 25 S's primary reliability risk is head gasket failure in pre‑1983 units, with elevated incidence in high‑load or overheating conditions. Vauxhall service data from 1982 noted increased warranty claims for coolant contamination and compression loss, while UK DVLA workshop records show frequent timing chain and carburettor faults in preserved examples. Infrequent oil changes and cooling system neglect accelerate wear, making adherence to service intervals critical.
Analysis derived from Vauxhall technical bulletins (1978–1986) and UK DVSA failure statistics (1985–1995). Repair procedures should follow manufacturer guidelines.
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The 25 S offers smooth power delivery and mechanical simplicity but demands diligent cooling system maintenance. Pre‑1983 units are prone to head gasket failure; post‑1983 engines with MLS gaskets are more robust. Regular oil changes, correct valve clearances, and carburettor upkeep are essential for longevity beyond 100,000 miles.
Top issues include head gasket failure (pre‑1983), timing chain stretch, carburettor wear, and coolant leaks from the cast‑iron block. These are documented in Vauxhall service bulletins and classic car workshop data.
The 25 S powered the Carlton Mk1 (1978–1986), Viceroy (1978–1982), and Senator A (1978–1986). It was never used in Cavalier, Chevette, or later Omega lines.
Modest gains are possible: performance camshafts, twin‑carb manifolds, or ported heads can yield ~10–15% more power. However, the OHV inline‑six design limits high‑rpm potential. Most owners retain stock tune for authenticity and reliability.
Typical consumption is 22–26 mpg UK (10.7–9.0 L/100km) in mixed driving due to large displacement and six-cylinder configuration. Highway cruising may reach 28 mpg UK, while city use can drop to 18 mpg. Carburettor condition and driving style significantly affect real-world figures.
No. The 25 S is a non‑interference OHV engine. If the timing chain fails, the pistons will not contact the valves, preventing catastrophic internal damage.
Vauxhall specifies SAE 20W‑50 mineral oil meeting API SC/CC. Modern classic‑car oils with ZDDP additive are recommended to protect flat‑tappet camshafts and valve train components.
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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