🏷️ Basic Information

Make:

Mercedes-Benz

Model:

350 SD Turbo

Year:

1991

Chassis Code:

W126

Engine Code:

OM603.960

👋 Introduction

Market Position:

The 1991 Mercedes-Benz 350 SD Turbo (W126 chassis) represented the pinnacle of diesel luxury sedans, competing with other high-end marques. It offered exceptional build quality, comfort, and the rugged reliability associated with Mercedes-Benz diesel powertrains.

Competitive Analysis:

Competitors included models from BMW (e.g., 7 Series diesel variants where available), Jaguar, and other premium manufacturers. The 350 SD Turbo distinguished itself with its robust diesel engine and characteristic Mercedes-Benz ride and build quality.

Key Features:

Turbocharged inline-six diesel engine, luxurious interior appointments, advanced safety features for its era (e.g., ABS), robust construction, excellent long-distance cruising capability, and a legendary Mercedes-Benz diesel reputation for durability.

📋 Manual Details

Coverage Areas:

Full factory service and repair for 1991 Mercedes-Benz 350 SD Turbo (W126 chassis)

Page Count:

Estimated 1000+ pages (typical for comprehensive factory manuals of this era)

Manual Type:

Factory Service Manual / Repair Manual

Language:

English

Format:

Digital (PDF), likely searchable and printable

Digital Format Benefits:

Searchable text for quick information retrieval, zoomable diagrams, easily printable specific sections.

📖 Manual Coverage

Systems Covered:

Engine (OM603.960), Fuel System, Diesel Injection System, Turbocharger, Cooling System, Lubrication System, Exhaust System, Transmission (4-speed Automatic), Drivetrain, Suspension (Front & Rear), Steering, Brakes (ABS), Electrical System (Wiring Diagrams, Components), Climate Control (HVAC), Body & Chassis, Interior Trim, Diagnostic Procedures, Troubleshooting

Electrical System Details:

Complete wiring diagrams for all vehicle systems, component location charts, troubleshooting guides for electrical faults, fuse and relay identification.

Procedures Included:

Routine maintenance, component removal and installation, major overhauls, diagnostic troubleshooting, electrical system repair, brake system service, suspension and steering alignment, fuel system diagnosis and repair, turbocharger servicing, climate control system repair, body panel alignment and repair, interior component service

Engine Performance Tuning:

While not a performance tuning manual, it covers correct adjustment of injection timing and basic engine settings for optimal performance and emissions.

Wheel Alignment Specifications:

Provides front and rear wheel alignment specifications (caster, camber, toe) for proper handling and tire wear.

Technical Depth:

Comprehensive from basic maintenance and fluid changes to complete engine and transmission rebuilds, including detailed diagnostic flowcharts and specifications

Diagnostic Troubleshooting:

Detailed flowcharts for diagnosing common and uncommon issues, covering symptoms, probable causes, and corrective actions.

📊 Manual Specifications

File Format:

PDF

Print Quality:

High-resolution scans of original factory documents, ensuring clarity of text and diagrams

Binding Type:

N/A (Digital Format)

Paper Type:

N/A (Digital Format)

⚙️ Engine Specifications

Primary Engine:

3.5L Inline-6 Turbocharged Diesel (OM603.960)

Horsepower:

Approximately 134 hp @ 4000 rpm (varies slightly by market)

Torque:

Approximately 217 lb-ft @ 2400 rpm (varies slightly by market)

Fuel System:

Bosch inline mechanical fuel injection pump, indirect injection

Turbocharger Details:

Garrett AiResearch turbocharger, air-to-air intercooler

Bore Stroke:

91.0 mm x 108.6 mm

Compression Ratio:

22.0:1

Engine Management:

Electronic diesel control (EDC) system for fuel injection timing and quantity

Engine Disassembly Instructions:

Manual provides detailed step-by-step procedures for engine disassembly, including torque specifications, special tool requirements, and component clearances.

Cooling System Description:

Pressurized system with belt-driven water pump, radiator, thermostat, and expansion tank. Features a viscous fan clutch for temperature-dependent cooling.

Lubrication System Description:

Forced lubrication via engine-driven oil pump, oil filter, and oil cooler (if equipped). Includes oil pressure specifications and troubleshooting.

🔧 Transmission

Standard Transmission:

4-speed Automatic Transmission (722.4)

Optional Transmission:

N/A for the 350 SD Turbo model

Transmission Features:

Lock-up torque converter, driver-selectable modes (e.g., Economy/Sport)

Transmission Fluid Type:

Mercedes-Benz Specification 236.1 (e.g., Dexron II compatible)

📐 Dimensions

Wheelbase:

112.8 inches (2865 mm)

Length:

192.1 inches (4880 mm)

Width:

70.5 inches (1790 mm)

Height:

55.7 inches (1415 mm)

Front Track:

60.1 inches (1527 mm)

Rear Track:

59.2 inches (1503 mm)

Ground Clearance:

Approximately 6.0 inches (150 mm) unladen.

Curb Weight:

Approximately 3900 lbs (1770 kg)

Gross Vehicle Weight Rating:

Approximately 4960 lbs (2250 kg)

Towing Capacity:

Not typically specified for this luxury sedan; focus on passenger comfort and cargo.

🛡️ Safety Features

Safety Ratings:

NHTSA and IIHS ratings from this era are less standardized, but the W126 chassis was known for its robust safety cell and energy-absorbing crumple zones.

Active Features:

Anti-lock Braking System (ABS)

Passive Features:

Dual front airbags, energy-absorbing steering column, reinforced passenger cell, side-impact protection (door beams), three-point seat belts with pretensioners

Seat Belts:

Front and rear three-point seat belts, front seat belt height adjustment.

Brake System Type:

Four-wheel disc brakes with ABS

💡 Technology Features

Infotainment System:

Factory fitted AM/FM stereo radio with cassette player, power antenna, and speaker system. Optional CD player availability.

Driver Assistance Features:

ABS (Anti-lock Braking System), cruise control.

Connectivity:

N/A by modern standards; primarily focused on vehicle systems.

Climate Control System:

Automatic Climate Control (ACC) with electronic temperature and fan speed regulation, recirculate function, and diagnostic capabilities.

Lighting Features:

Halogen headlamps, fog lamps (optional/standard depending on market), interior courtesy lighting.

🔧 Maintenance

Oil Change Interval:

Typically every 3,000-5,000 miles or annually, depending on driving conditions and oil used. Consult manual for exact factory recommendations.

Air Filter Replacement:

Every 15,000-30,000 miles or as needed based on air quality. Consult manual.

Fuel Filter Replacement:

Every 15,000-30,000 miles. Crucial for diesel fuel system health. Consult manual.

Coolant Flush:

Every 2-3 years or 30,000-50,000 miles. Consult manual.

Engine Oil Type:

API CD/CE or ACEA B3/B4 rated diesel engine oil, SAE 15W-40 or 10W-30 recommended depending on climate. Consult manual for precise viscosity grade.

Engine Oil Capacity:

7.5 Liters (8.0 US Quarts) with filter change.

Coolant Type:

Mercedes-Benz Specification 325.0 (Ethylene Glycol based)

Brake Fluid Type:

DOT 3 or DOT 4

Power Steering Fluid:

Mercedes-Benz Specification 236.3 (Dexron II compatible)

Coolant Capacity:

Approximately 10.5 Liters (11.1 US Quarts)

Known Issues:

Potential issues include: Head gasket leaks, diesel injection pump wear, vacuum line degradation, early-generation ABS sensor failures, climate control blower motor issues, and potential for rust in common W126 areas (wheel arches, rocker panels). The OM603 engine is generally robust but requires meticulous maintenance.

Fuel Filter Part Number Example:

Example: Mann Filter WK 80 / Fleetguard FS1022 (confirm with manual)

Oil Filter Part Number Example:

Example: Mann Filter HU 719/3 x (confirm with manual)

📚 Vehicle History

Brand Heritage:

Mercedes-Benz has a long-standing heritage of engineering excellence, luxury, and innovation, particularly in diesel engine technology.

Diesel Technology Emphasis:

Mercedes-Benz was a pioneer in diesel passenger car technology, and the OM603 engine in the 350 SD Turbo reflects this legacy of durable and efficient diesel powertrains.

Model Evolution:

The W126 S-Class (produced 1979-1991) was a groundbreaking generation for Mercedes-Benz, setting new standards in automotive safety, comfort, and aerodynamics. The 'SD' designation signified a turbocharged diesel engine.

Chassis Designation:

W126 chassis was the second generation of the S-Class, succeeding the W116 and preceding the W140. It was renowned for its aerodynamic efficiency and integrated safety features.

Production Years:

1991 (as part of the W126 series)

Production Location:

Sindelfingen, West Germany