🏷️ Basic Information

Make:

Mercedes-Benz

Model:

350 SD Turbo

Year:

1991

Chassis Code:

W140

Engine Code:

OM603.970

👋 Introduction

Vehicle Segment:

Full-size Luxury Sedan

Historical Context:

Flagship model for Mercedes-Benz during its production era

Key Competitors:

BMW 7 Series, Audi V8, Lexus LS 400

Engineering Philosophy:

Over-engineered, robust construction, focus on comfort and durability

Diesel Offering:

One of Mercedes-Benz's premium diesel offerings, known for torque and longevity

📋 Manual Details

Primary Coverage:

Vehicle Repair and Service

Secondary Coverage:

Maintenance, Diagnostics, Troubleshooting

Estimated Page Count:

600-800

Type:

Repair Service Manual

Language:

English

Format:

PDF Download

📖 Manual Coverage

Engine Mechanical:

Complete overhaul, component testing, torque specifications, timing procedures

Engine Management:

Fuel injection system (Bosch KE-Jetronic), ignition system, emission control systems, sensor diagnostics

Transmission:

Automatic transmission (722.3/722.4) service, diagnostics, fluid specifications, valve body operation

Brakes:

ABS (Anti-lock Braking System) diagnosis and repair, hydraulic system service, pad and rotor replacement, fluid types

Suspension Steering:

Front and rear suspension components, hydraulic self-leveling suspension (optional), steering system, power steering system

Electrical System:

Wiring diagrams, component testing, fuse and relay identification, starter, alternator, battery service, lighting systems

HVAC:

Air conditioning system service, climate control operation, heater core replacement, blower motor diagnostics

Body Chassis:

Body panel removal and installation, door mechanisms, glass replacement, exterior trim, chassis components

Routine Maintenance:

Oil changes, filter replacements, fluid checks and top-offs, belt inspections and replacements

Troubleshooting:

System-specific fault finding, diagnostic flowcharts, common problems and solutions

Repair Overhaul:

Engine rebuild procedures, transmission disassembly and reassembly, component replacement guidelines

Diagnostics:

On-board diagnostics (OBD) interpretation for the era, sensor testing, electronic module troubleshooting

Depth:

Comprehensive (from basic maintenance to full engine/transmission rebuilds)

Target Audience:

Professional Technicians, Advanced DIYers

📊 Manual Specifications

Quality:

High-resolution, searchable PDF

Searchability:

Full text search enabled

Printable:

Yes, designed for printing specific sections or the entire manual

Digital Binding:

N/A (Digital Download)

Digital Paper:

N/A (Digital Download)

⚙️ Engine Specifications

Engine Type:

Inline 6-Cylinder Turbo Diesel

Displacement:

3.5 Liters (3449 cc)

Bore X Stroke:

91.0 mm x 88.3 mm

Compression Ratio:

21.0:1

Aspirated By:

Turbocharged

Horsepower:

148 hp @ 4000 rpm

Torque:

232 lb-ft @ 2400 rpm

Fuel Delivery:

Bosch KE-Jetronic Electronic Fuel Injection with Diesel Turbocharging

Fuel Type:

Diesel Fuel

Engine Oil Type:

API CD or CE, SAE 15W-40 (check manual for specific viscosity based on temperature)

Engine Oil Capacity:

7.5 Liters (8.0 US Quarts)

Coolant Type:

MB 325.0 (Glysantin G48 or equivalent blue ethylene glycol coolant)

🔧 Transmission

Transmission Type:

4-Speed Automatic

Transmission Model:

722.3 / 722.4

Optional Transmission:

None offered for 350 SD Turbo in 1991

Shift Modes:

Comfort (C) / Sport (S)

Transmission Fluid Type:

MB 236.1 (Dexron II or equivalent)

Transmission Fluid Capacity:

8.0 Liters (8.5 US Quarts) for total capacity, 3.5 Liters (3.7 US Quarts) for drain and fill

📐 Dimensions

Length:

197.9 inches (5027 mm)

Width:

74.0 inches (1880 mm)

Height:

57.4 inches (1458 mm)

Wheelbase:

118.1 inches (3000 mm)

Curb Weight:

4400 lbs (2000 kg) approx.

Gross Vehicle Weight Rating:

5512 lbs (2500 kg) approx.

🛡️ Safety Features

NHTSA Ratings:

Not directly comparable to modern standards, but built to high safety standards of the era.

ABS:

Standard Anti-lock Braking System (ABS)

Airbags:

Driver airbag standard

Seatbelts:

Pretensioning seatbelts

Body Structure:

High-strength steel construction, crumple zones

💡 Technology Features

Audio System:

Factory premium sound system, often with cassette player and AM/FM radio.

Cruise Control:

Standard electronic cruise control.

Climate Control:

Automatic climate control (often dual-zone).

Telephony:

Optional integrated telephone system (era-appropriate, large handset).

🔧 Maintenance

Oil Change Interval:

Every 7,500-10,000 miles or 12 months, whichever comes first (refer to manual for exact spec).

Transmission Fluid Interval:

Every 30,000-50,000 miles (check for specific recommendation, often considered 'lifetime' by manufacturer but recommended for service).

Air Filter Interval:

Every 15,000-30,000 miles or as needed based on driving conditions.

Fuel Filter Interval:

Every 20,000-30,000 miles.

Common Diesel Issues:

Glow plug failure, injector pump issues, turbocharger wear, pre-chamber issues, vacuum leaks affecting various systems.

Common W140 Issues:

Hydraulic suspension leaks (if equipped), SRS system issues, vacuum operated door locks/central locking faults, window regulator failures, biodegradable wiring harness degradation (later models, but potential for some).

Fuel System Specifics:

KE-Jetronic system can be complex to diagnose; requires specific tools and knowledge.

📚 Vehicle History

Brand Legacy:

Mercedes-Benz has a long history of producing robust, high-quality diesel engines and luxury vehicles.

W140 Introduction:

The W140 chassis was introduced in 1991 as the successor to the W126 S-Class, representing a significant leap in technology and size.

Sd Designation:

'SD' denotes the Diesel model.

Production Period:

1991-1998 (W140 chassis)

Manufacturing Location:

Germany

🏆 Awards & Recognition

Vehicle Prestige:

The W140 S-Class was widely regarded as one of the most advanced and luxurious cars of its time.

Durability Perception:

Generally perceived as highly durable and capable of high mileage when properly maintained.