🏷️ Basic Information

Make:

Mercedes-Benz

Model:

350 SD Turbo

Model Code:

W140.135

Year:

1991

👋 Introduction

Market Segment:

Luxury Full-Size Sedan

Target Audience:

Affluent individuals seeking comfort, performance, and advanced engineering.

Key Competitors:

BMW 7 Series (E32), Lexus LS 400 (UCF10), Cadillac Sedan DeVille.

Brand Heritage:

Reputation for robust engineering, luxury appointments, and pioneering automotive technology.

Model Characteristics:

Exceptional build quality, refined ride, powerful yet economical diesel engine, advanced (for its time) features.

Value:

Essential resource for owners and independent mechanics to maintain and repair the sophisticated W140 chassis, ensuring longevity and optimal performance.

📋 Manual Details

Engine Coverage:

OM603.971 Diesel Turbocharged 3.5L Inline-6

Transmission Coverage:

4-Speed Automatic Transmission (722.3xx series)

Chassis Coverage:

Suspension, Steering, Brakes, Body

Electrical Coverage:

Wiring Diagrams, ECUs, Lighting, Accessories

Estimated Page Count:

Approximately 1500-2000 pages (typical for comprehensive workshop manuals of this era)

Type:

Workshop Service and Repair Manual

Language:

English

Format:

PDF Download

📖 Manual Coverage

Engine Mechanical:

Engine removal/installation, cylinder head, pistons, crankshaft, camshaft, timing system, oil system, cooling system, fuel injection system (Bosch VE),

Engine Performance:

Turbocharger system, intercooler, emissions control system, diagnostic procedures for engine performance.

Transmission Manual:

Automatic transmission removal/installation, internal components, torque converter, hydraulic system, electronic control unit (ECT).

Drivetrain:

Driveshafts, differential, axles.

Suspension Front:

Independent front suspension, shock absorbers, springs, control arms, anti-roll bar.

Steering:

Power steering system, steering gear, steering column, steering wheel.

Brakes Front:

Vented disc brakes, calipers, brake pads, rotors.

Brake Control:

Anti-lock Braking System (ABS) components and diagnostics.

Body Exterior:

Body panels, doors, hood, trunk, bumpers, glass, seals.

HVAC:

Heating, Ventilation, and Air Conditioning (HVAC) system components, refrigerant, controls.

Electrical Lighting:

Headlights, taillights, interior lighting, fog lights.

Electrical Accessories:

Power windows, power locks, power mirrors, sunroof, cruise control, central locking system.

Electrical Audio:

Radio, speakers, antenna.

Electrical ECU:

Engine Control Unit (ECU) and transmission control unit (TCU) diagnostics and component identification.

Wiring Diagrams:

Comprehensive electrical schematics and wiring diagrams for all vehicle systems.

Suspension Rear:

Independent rear suspension, multi-link setup, shock absorbers, springs, anti-roll bar.

Brakes Rear:

Disc brakes, calipers, brake pads, rotors.

Body Interior:

Interior trim, seats, dashboard, headliner, carpeting.

Electrical Instruments:

Instrument cluster, gauges, warning lamps.

Routine Maintenance:

Oil and filter changes, air filter replacement, fuel filter replacement, coolant flush, spark plug replacement (if applicable), belt inspection/replacement.

Troubleshooting:

Diagnostic procedures for common issues, fault code interpretation, symptom-based troubleshooting guides.

Engine Repair:

Complete engine overhaul procedures, including disassembly, inspection, measurement, and reassembly of internal components.

Transmission Repair:

Automatic transmission repair and overhaul, including clutch pack replacement, valve body servicing, and seal replacement.

Brake System Repair:

Brake pad and rotor replacement, caliper servicing, brake line replacement, bleeding procedures, ABS system component replacement.

Suspension Steering Repair:

Replacement of control arms, ball joints, tie rod ends, shock absorbers, springs, steering gear.

Electrical Diagnostics:

Diagnosis and repair of electrical faults, testing of sensors, actuators, and control modules.

Bodywork Repair:

Procedures for body panel removal/installation, collision repair guidance, glass replacement.

HVAC Repair:

Diagnosis and repair of HVAC system faults, refrigerant system servicing, component replacement.

Torque Specifications:

Detailed torque specifications for all critical fasteners.

Depth:

Comprehensive from basic maintenance to complete engine and transmission rebuilds, including advanced diagnostics and electrical troubleshooting.

📊 Manual Specifications

PDF Quality:

High-resolution, searchable text and clear images.

Printable:

Printable pages

Binding:

N/A (Digital PDF)

Paper:

N/A (Digital PDF)

⚙️ Engine Specifications

Engine Code:

OM603.971

Engine Type:

Inline-6 Cylinder, Overhead Camshaft (OHC), Diesel

Displacement:

3.5 Liters (3449 cc)

Aspiration:

Turbocharged with Intercooler

Horsepower:

148 hp @ 4000 rpm (approx.)

Torque:

255 lb-ft @ 2400 rpm (approx.)

Fuel Type:

Diesel Fuel

Injection System:

Bosch VE Rotary Injection Pump, Indirect Injection

Cooling Type:

Liquid-Cooled

Oil Capacity:

8.0 Liters (with filter)

Recommended Oil:

API CD or CE, SAE 15W-40 or 10W-40 (refer to manual for exact specifications based on climate).

🔧 Transmission

Type:

4-Speed Automatic Transmission

Model Code:

722.3xx series (e.g., 722.371)

Type:

Not applicable for this specific model variant

Electronic Control:

Electronically Controlled Transmission (ECT) for optimized shift points and economy.

Transmission Fluid Type:

MB 236.6 (Shell Donax TX or equivalent)

Fluid Capacity:

Approximately 8.0 Liters (for complete drain and fill, including torque converter)

📐 Dimensions

Length:

5163 mm (203.3 in)

Width:

1886 mm (74.3 in)

Height:

1487 mm (58.5 in)

Wheelbase:

3040 mm (119.7 in)

Curb Weight:

Approx. 1900 kg (4189 lbs)

Gross Vehicle Weight Rating:

Approx. 2470 kg (5445 lbs)

Trunk Volume:

Approx. 520 Liters (18.4 cu ft)

🛡️ Safety Features

Crash Test Results:

Information for this specific year and model is limited in readily available public databases, as official standardized testing was less prevalent than today. However, Mercedes-Benz historically prioritized safety.

ABS:

Standard Anti-lock Braking System (ABS)

Airbags:

Driver's side airbag standard.

Body Construction:

Reinforced safety cage, crumple zones, side-impact protection beams.

Seat Belts:

Front seat belt pretensioners.

💡 Technology Features

Audio System:

Factory fitted AM/FM stereo cassette player with integrated amplifier and speakers.

Display:

Instrument cluster with analog gauges and warning lamps. Some models may have a basic trip computer display.

Cruise Control:

Standard electronic cruise control.

Traction Control:

Could be equipped with ASR (Acceleration Slip Regulation) depending on market and options.

Connectivity Options:

Basic connectivity via radio antenna; no integrated Bluetooth or telematics in the modern sense.

🔧 Maintenance

Oil Change Interval:

Every 7,500 - 10,000 miles or 12 months (whichever comes first), or as indicated by the car's service indicator system (if equipped and functional).

Transmission Fluid Interval:

Every 30,000 - 50,000 miles (recommended for longevity, though some sources suggest longer intervals).

Fuel Filter Interval:

Every 15,000 - 20,000 miles.

Air Filter Interval:

Every 15,000 - 20,000 miles or as needed based on driving conditions.

Coolant Flush Interval:

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

Coolant Type:

Mercedes-Benz Coolant/Antifreeze (e.g., G48 or equivalent, typically a phosphate-free blue/green ethylene glycol mix)

Brake Fluid Type:

DOT 3 or DOT 4

Power Steering Fluid:

MB 236.3 (Dexron II or equivalent)

Vacuum System:

Vacuum leaks affecting central locking, door locks, and HVAC controls are common due to aging rubber components.

Wiring Harness:

Degradation of insulation on wiring harnesses, particularly around the engine bay, can lead to electrical gremlins.

Suspension:

Worn suspension bushings, ball joints, and potential leaks in self-leveling rear suspension (if equipped).

Head Gasket:

While the OM603 is generally robust, head gasket issues can arise with age or overheating.

Glow Plugs:

Failure of glow plugs and the associated control module can lead to hard starting in cold weather.

Immobilizer:

Early electronic immobilizer systems can sometimes be problematic if the key transponder or control unit fails.

📚 Vehicle History

Founded:

1926 (merger of Benz & Cie. and Daimler-Motoren-Gesellschaft)

Reputation:

Pioneer in automotive engineering, safety innovations, and luxury vehicles.

Generation:

W140 Generation (introduced in 1991, replacing the W126 S-Class)

Development Focus:

Emphasis on superior ride comfort, advanced technology, and a more imposing presence than its predecessor.

Production Years:

1991-1998 (for the W140 chassis)

Manufacturing Locations:

Sindelfingen, Germany

Diesel Variant Significance:

The 350 SD Turbo represented Mercedes-Benz's continued commitment to refined and efficient diesel technology in their flagship luxury sedan, offering excellent fuel economy for its size.

🏆 Awards & Recognition

Industry Acclaim:

While specific awards for the 1991 350 SD Turbo are not prominently documented, the W140 S-Class generation was generally lauded for its engineering prowess and comfort, solidifying Mercedes-Benz's leadership in the luxury sedan market.