🏷️ Basic Information

Make:

Mercedes-Benz

Model:

300 SEL

Model Code:

W126 (Long Wheelbase)

Production Years Covered:

1988, 1989, 1990, 1991

Engine Codes:

M103.980

Chassis Codes:

W126.025

👋 Introduction

Segment:

Luxury Sedan (Full-Size)

Target Audience:

Owners seeking to maintain or repair their W126 chassis Mercedes-Benz 300 SEL, including independent repair shops and knowledgeable DIY enthusiasts.

Competitors Era:

BMW 7 Series (E32), Audi V8 Quattro, Cadillac DeVille, Lincoln Town Car.

Vehicle Highlights:

The 300 SEL (W126) represents the pinnacle of Mercedes-Benz engineering for its era, offering unparalleled comfort, build quality, and a refined driving experience. Known for its robust construction, sophisticated suspension systems (including optional self-leveling and 4MATIC), and a powerful yet smooth inline-six engine.

Dealer Equivalence:

Identical to the manuals used by authorized Mercedes-Benz dealerships.

📋 Manual Details

Coverage Type:

Comprehensive Factory Service and Repair

Specific Models And Years:

Mercedes 300 SEL (1988-1991)

Estimated Pages:

Extensive (Specific count not provided, but implied to be highly comprehensive)

Type:

Service and Repair Manual

Language:

English

Format:

Digital Download (PDF)

📖 Manual Coverage

Engine:

Engine oil and filter change, valve clearance adjustment/checking, idle speed checking/adjustment, injection timing, fuel filter replacement, air filter replacement, V-belt/Poly V-belt inspection/tensioning, intake/exhaust manifold seating, oxygen sensor replacement, spark plug inspection/replacement, coolant level/antifreeze protection, cooling/heating system, coolant replacement, engine mount bolts, engine stop adjustment.

Drivetrain:

Manual transmission oil change/level check, automatic transmission fluid and filter change/level check, transfer case fluid change/level check, clutch disk wear inspection, clutch system fluid check/correction, clutch system inspection, throttle linkage lubrication/inspection, steering play check, steering bolts re-tightening, front axle oil level check, rear axle oil change/level check, rear axle mount adjustment.

Suspension And Steering:

Suspension and body structure inspection, level control (ADS, 4MATIC) fluid level, self-leveling suspension inspection, front axle ball joint inspection, ball joint inspection (special tool), drive shaft flexible coupling inspection.

Brakes:

Brake fluid level check, brake lines inspection, brake pads and disc thickness inspection, brake disks inspection/cleaning, parking brake cable inspection, parking brake adjustment, brake fluid replacement, brake test/parking brake check.

Electrical:

Warning and indicator lamp checks, battery fluid level check.

Body And Chassis:

Component condition inspection, lines and hoses inspection, water leakage and corrosion inspection, wheel inspection/rotation, tire inspection, tire pressure correction, wheel bolt tightening, exhaust flange re-tightening, exhaust system connections re-tightening, water drain cleaning, engine compartment lower panel removal/installation, door hinge lubrication, door lock lubrication, hydraulic top fluid level check/correction, sunroof rail cleaning/greasing, soft top locking tab check, windshield washer fluid level check/correction, antenna mast cleaning, headlamp and exterior lamp inspection, windshield wiper and washer inspection, windshield wiper blade replacement, hood lubrication, lower noise encapsulation panel removal/installation, body paint damage inspection.

Climate Control:

Heating and ventilation dust filter replacement, active charcoal filter replacement, recirculating air filter replacement, AC refrigerant charge check/correction.

Diagnostics:

Troubleshooting procedures and diagnostic flowcharts for various systems, including engine, electrical, and fuel systems.

Maintenance:

Routine fluid changes (oil, transmission, differential, brake, washer), filter replacements (oil, air, fuel, cabin), belt inspections and adjustments, spark plug replacement, coolant checks, battery checks.

Repair:

Component replacement (e.g., oxygen sensor, fuel filter, brake components, suspension components), system adjustments (e.g., idle speed, injection timing, parking brake), leak repairs (e.g., water, fluid), electrical component testing (warning lamps).

Inspection:

Comprehensive inspection of engine components, lines, hoses, suspension, body structure, water leaks, corrosion, tires, brakes, steering, fuel system, electrical system, safety belts, backrest locks.

Lubrication:

Throttle linkage, door hinges, door locks, sunroof rails, hood.

Depth:

Factory-level, detailed diagnostic procedures, repair instructions, and component specifications. Suitable for professional technicians and advanced DIY enthusiasts.

📊 Manual Specifications

Format:

PDF

Searchability:

Fully searchable text

Printability:

All pages printable

Binding:

N/A (Digital Download)

Paper Type:

N/A (Digital Download)

File Quality:

Real files, not scans

⚙️ Engine Specifications

Engine Type:

Inline-6 Cylinder, DOHC

Displacement:

3.0 Liters (2960 cc)

Bore X Stroke:

88.5 mm x 80.25 mm

Compression Ratio:

9.2:1

Horsepower:

189 hp @ 5700 rpm (approx.)

Torque:

207 lb-ft @ 4400 rpm (approx.)

Fuel Delivery:

Bosch KE-Jetronic Fuel Injection (Mechanical/Electronic Hybrid)

Octane Rating:

Premium Unleaded (91 RON or higher)

Coolant Capacity:

Approx. 9.0 Liters (with heater core)

Oil Capacity:

Approx. 7.5 Liters (with filter)

Recommended Oil Viscosity:

SAE 15W-40 or 10W-40 (depending on climate)

🔧 Transmission

Type:

4-Speed Automatic (722.3 / 722.4 series)

Type:

None for 300 SEL in these years

Transmission Fluid Type:

MB 236.1 / MB 236.2 / Dexron II (refer to manual for exact specification)

Transmission Fluid Capacity:

Approx. 7.0 Liters (for torque converter refill)

📐 Dimensions

Wheelbase:

3075 mm (121.1 inches)

Length:

5030 mm (198.0 inches)

Width:

1790 mm (70.5 inches)

Height:

1430 mm (56.3 inches)

Curb Weight:

Approx. 1750 kg (3858 lbs)

Standard Tire Size:

205/65R15

Wheel Bolt Pattern:

5 x 112 mm

Wheel Offset:

ET 37

🛡️ Safety Features

Crash Test Data:

While specific ratings for this exact period are less standardized than today, the W126 chassis was renowned for its robust safety cage, crumple zones, and energy-absorbing steering column, setting benchmarks for its time.

Braking System:

Anti-lock Braking System (ABS) standard.

Restraints:

Driver and front passenger airbags (introduced in later W126 models), front seatbelt pre-tensioners.

Body Structure:

Reinforced passenger cell, energy-absorbing front and rear sections.

💡 Technology Features

Audio System:

Factory-installed premium sound systems, often with cassette decks. CD changers were an option on later models.

Cruise Control:

Standard cruise control system.

Automatic Climate Control:

Optional or standard automatic climate control with advanced features for the era.

Exterior Features:

Power-adjustable side mirrors, heated mirrors, central locking, power antenna.

🔧 Maintenance

Engine Oil And Filter:

Every 7,500 - 10,000 miles or annually (refer to manual for specific driving conditions and exact intervals).

Transmission Fluid And Filter:

Every 30,000 - 50,000 miles (often considered 'lifetime' by some, but periodic changes are recommended for longevity).

Brake Fluid:

Every 2 years (hygroscopic nature absorbs moisture).

Coolant:

Every 2-4 years, depending on coolant type used.

Power Steering Fluid:

MB 236.3 or equivalent hydraulic fluid (check manual).

Brake Fluid:

DOT 3 or DOT 4 (check manual for specific recommendations).

Common Problems:

Head gasket leaks (M103 engine), cooling system component degradation (hoses, expansion tank), vacuum leak issues affecting engine performance, window regulator failures, SRS system faults (airbag warning light), ABS sensor failures, fuel distributor issues (KE-Jetronic), self-leveling suspension leaks (if equipped).

📚 Vehicle History

Manufacturer Legacy:

Mercedes-Benz has a long-standing reputation for engineering excellence, luxury, and safety, dating back to the early days of the automobile. The W126 generation represented a significant evolution in the brand's S-Class lineage.

W126 Generation:

The W126, produced from 1979 to 1991, was a groundbreaking design for Mercedes-Benz. The 300 SEL variant, introduced later in the model's lifecycle, offered a more accessible yet still luxurious six-cylinder option in the long-wheelbase body style.

Manufacturing Location:

Germany

🏆 Awards & Recognition

Industry Accolades:

The W126 generation as a whole received numerous accolades for its design, engineering, and luxury. It was widely considered one of the finest sedans in the world during its production run.