🏷️ Basic Information

Make:

Mercedes-Benz

Model:

350 SD Turbo

Year:

1991

Chassis Code:

W140

Engine Code:

OM603.970

👋 Introduction

Segment:

Full-size Luxury Sedan (S-Class)

Target Audience:

Owners seeking to perform DIY maintenance and repairs, independent repair shops, automotive technicians.

Competitors 1991:

BMW 7 Series (E32), Lexus LS 400 (XF10), Cadillac DeVille

Vehicle Features:

Emphasis on luxury, comfort, advanced technology for its era, robust build quality, and powerful yet efficient diesel engine.

Cost Savings:

Significant savings on dealership labor costs for maintenance and repairs.

Knowledge Acquisition:

Empowers owners with in-depth knowledge of their vehicle's systems and repair procedures.

📋 Manual Details

Primary Coverage:

Full Service, Repair, Diagnostics, Electrical, Powertrain, Chassis

Secondary Coverage:

Maintenance, Troubleshooting, Component Replacement, Bodywork

Estimated Pages:

1000+

Type:

Workshop Manual (WSM) / Service Repair Manual

Language:

English

Format:

Digital Download (PDF expected)

File Type:

Likely PDF, potentially with searchable text and vector graphics for diagrams.

Quality:

Professional quality, designed for clear reproduction of diagrams and text.

Binding:

N/A (Digital Download)

Paper:

N/A (Digital Download)

📖 Manual Coverage

Engine:

OM603.970 3.5L Inline-6 Turbo Diesel, fuel injection, lubrication, cooling, exhaust

Transmission:

4-speed Automatic Transmission (722.3/722.4 series), gear shifts, hydraulics, torque converter

Drivetrain:

Rear-Wheel Drive (RWD), differential, driveshafts, axle assembly

Suspension:

Independent front and rear suspension, springs, shock absorbers, control arms, anti-roll bars

Brakes:

Hydraulic disc brakes (front and rear), ABS (Anti-lock Braking System), parking brake

Steering:

Hydraulic power steering system, steering column, steering gear

Electrical System:

Battery, alternator, starter, lighting, ignition, wiring diagrams, fuses, relays, power windows, seats

Climate Control:

Automatic Climate Control (ACC), HVAC system, A/C compressor, refrigerant, heating core, blower motor

Body And Chassis:

Body structure, doors, hood, trunk, glass, interior trim, sound deadening

Maintenance:

Oil changes, filter replacements, fluid checks and top-offs, belt inspections and replacement, spark plug replacement (if applicable, though diesel)

Engine Repair:

Engine overhaul, cylinder head service, piston and ring replacement, crankshaft and bearing service, turbocharger diagnostics and repair

Transmission Repair:

Transmission fluid and filter changes, seal replacement, valve body diagnostics, clutch pack service (for automatic)

Brake Repair:

Brake pad and rotor replacement, brake caliper service, brake fluid flush and bleed, ABS system diagnosis and repair

Electrical Troubleshooting:

Wiring harness inspection, component testing, fault code retrieval and interpretation (OBD-I related), diagnostic procedures

Suspension And Steering Repair:

Alignment procedures, component replacement (bushings, ball joints, tie rods), power steering system repair

Diagnostics:

System-specific troubleshooting guides, common fault diagnosis, diagnostic tool usage (where applicable)

Depth:

Comprehensive: Covers routine maintenance, detailed component removal/installation, troubleshooting, and system overhauls.

Diagnostic Level:

Advanced diagnostic procedures, including interpretation of symptoms and fault codes.

Repair Level:

Full repair and rebuild procedures for major and minor components.

⚙️ Engine Specifications

Engine Type:

OM603.970 Inline 6-Cylinder Diesel with Turbocharger

Displacement:

3.5 Liters (3449 cc)

Bore X Stroke:

91.0 mm x 88.3 mm

Compression Ratio:

22.0:1

Horsepower Net:

134 hp @ 4000 rpm

Torque Net:

239 lb-ft @ 2400 rpm

Fuel Injection:

Bosch VE Rotary Injection Pump (Mechanical)

Fuel Type:

Diesel Fuel

Cooling Type:

Liquid-Cooled, Pressurized System

Oil Capacity:

7.5 Liters (8.0 US Quarts)

Oil Filter Part Number:

M-B: 000 180 26 09 (Typical, confirm specific)

Turbo Model:

Garrett (Specific model may vary, consult manual)

🔧 Transmission

Transmission Type:

4-Speed Automatic Transmission

Transmission Model Code:

722.3XX or 722.4XX series (confirm specific)

Optional Transmission:

None offered for 350 SD Turbo in this market.

Transmission Fluid Type:

MB 236.6 Specification Automatic Transmission Fluid (ATF)

Transmission Fluid Capacity:

Approx. 8.0 Liters (17.0 US Pints) for a complete fill (consult manual for exact capacity).

Transmission Filter Part Number:

M-B: 140 277 00 95 (Typical, confirm specific)

📐 Dimensions

Length:

approx. 5113 mm (199.5 in)

Width:

approx. 1886 mm (74.3 in)

Height:

approx. 1447 mm (57.0 in)

Wheelbase:

approx. 3040 mm (119.7 in)

Curb Weight:

approx. 1860 kg (4100 lbs)

Gross Vehicle Weight Rating Gvwr:

Consult vehicle plate, typically around 2400 kg (5291 lbs)

Trunk Volume:

approx. 500 Liters (17.7 cu ft)

🛡️ Safety Features

NHTSA Ratings 1991:

Not directly available for 1991 models in the format of modern ratings. Known for robust build.

ABS:

Standard Anti-lock Braking System (ABS)

Traction Control:

Optional Acceleration Slip Regulation (ASR) may have been available on some models.

Airbags:

Driver's airbag standard, passenger airbag optional or standard depending on market/trim.

Seatbelts:

Front and rear seat belts with pretensioners.

Body Structure:

High-strength steel body structure with crumple zones.

💡 Technology Features

Audio System:

Factory premium audio system with AM/FM radio, cassette player. CD changer may be optional.

Navigation:

Optional early GPS navigation system (very basic by modern standards).

Cruise Control:

Standard cruise control system.

Parking Aids:

No factory parking sensors or backup cameras on this model.

Connectivity Features:

Limited by era; primarily focused on internal vehicle systems, not external connectivity like Bluetooth or Wi-Fi.

Seat Adjustment:

Power adjustable front seats with memory function.

Climate Control System:

Dual-zone automatic climate control (ACC) with recirculation and air quality sensors.

🔧 Maintenance

Oil Change Interval:

Every 10,000 - 15,000 km (6,000 - 9,000 miles) or 12 months, whichever comes first (confirm in manual).

Transmission Service Interval:

Every 50,000 - 60,000 km (30,000 - 37,000 miles) for fluid and filter change (confirm in manual).

Coolant Flush Interval:

Every 2 years or 40,000 km (25,000 miles) (confirm in manual).

Fuel Filter Replacement:

Every 40,000 - 60,000 km (25,000 - 37,000 miles) (confirm in manual).

Engine Oil Specification:

MB 229.1 or API CD/CE rated Diesel Engine Oil, SAE 15W-40 or 10W-40 depending on climate.

Coolant Specification:

MB 325.0 or equivalent G48 coolant (Blue/Green)

Brake Fluid Specification:

DOT 3 or DOT 4 brake fluid

Common Issues Diesel Engine:

Glow plug system issues, injection pump seal leaks, potential turbocharger wear, EGR system (if fitted) clogging.

Common Issues Electronics:

Door lock vacuum actuators failure, window regulator issues, CAN-bus (early systems) glitches, wiring harness degradation due to age.

Common Issues Suspension Steering:

Hydraulic suspension self-leveling system (SLS) issues (if equipped), control arm bushing wear, power steering hose leaks.

📚 Vehicle History

Mercedes Benz Legacy:

Long-standing reputation for engineering excellence, luxury, durability, and pioneering automotive technology.

W140 Introduction:

The W140 platform debuted in 1991 as the successor to the W126 S-Class, representing a significant technological leap and increase in size.

350 Sd Turbo Significance:

The 'SD' designation historically meant 'Spezial Diesel', and this model brought a torquey, efficient turbocharged diesel to the flagship S-Class lineup, offering an alternative to the V8 and V12 gasoline engines.

Production Years W140:

1991-1998

Assembly Location:

Sindelfingen, Germany

🏆 Awards & Recognition

General Recognition:

The W140 platform, while initially criticized for its bulk, is now recognized as a robust and durable engineering feat, representing the pinnacle of Mercedes-Benz technology at the time.

Reliability Reputation:

Reputation for long-term durability if maintained properly. Diesel engines are known for longevity.

Iso Certification Impact:

Reflects Mercedes-Benz's adherence to stringent quality control and manufacturing standards prevalent in German automotive engineering.