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Introduction
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Market Position
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Positioning:
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The W123 chassis represented Mercedes-Benz's commitment to robust engineering, durability, and luxury in the mid-size executive segment. It competed against other European luxury sedans and wagons.
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Competitive Analysis
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Competitors:
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BMW 5 Series (E28), Audi 100/200, Volvo 240 Series, Peugeot 505.
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Key Features
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Vehicle Highlights:
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Exceptional build quality, legendary durability and reliability, comfortable ride, powerful diesel engines (popular variants), refined interior, strong safety features for its era.
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Diesel Engine Reputation:
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The OM617 turbo-diesel engine in particular is famed for its extreme durability, longevity, and fuel efficiency, often reaching hundreds of thousands of miles with proper maintenance.
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Manual Coverage
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Systems Covered
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Powertrain:
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Engine (gasoline and diesel), Fuel System, Exhaust System, Cooling System, Lubrication System
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Transmission:
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Manual and Automatic Transmissions, Drivetrain components (driveshafts, differential)
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Chassis:
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Suspension (front and rear), Steering System, Brakes (hydraulic, parking brake), Wheels and Tires
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Electrical:
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Complete 12V Electrical System, Battery, Charging System (alternator), Starting System, Ignition System, Lighting, Instrumentation, Wiper/Washer System, Power Accessories
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Body And Interior:
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Body structure, Doors, Hood, Trunk, Bumpers, Glass, Seats, Interior trim, Heating and Air Conditioning (HVAC)
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Climate Control:
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Detailed information on the HVAC system, including blower motor, evaporator, heater core, and vacuum actuators.
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Procedures Included
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Maintenance:
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Scheduled maintenance, Oil changes, Filter replacements, Lubrication points, Belt checks and replacement
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Diagnostics And Troubleshooting:
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System diagnostics, Fault identification, Step-by-step troubleshooting guides, Diagnostic trouble codes (if applicable for the era)
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Repair And Overhaul:
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Component removal and installation, Engine overhaul procedures, Transmission rebuilds, Brake system repairs, Electrical component replacement
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Adjustments:
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Valve adjustments, Ignition timing adjustments, Carburetor adjustments (if applicable), Parking brake adjustments
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Engine Disassembly Reassembly:
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Step-by-step instructions for complete engine overhaul, including cylinder head removal, piston replacement, crankshaft inspection, and camshaft timing.
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Brake System Overhaul:
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Detailed procedures for caliper rebuilding, master cylinder replacement, brake line flaring and installation, and bleeding the brake system.
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HVAC System Service:
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Information on diagnosing and repairing the heating, ventilation, and air conditioning systems, including component replacement and refrigerant handling (if applicable to manual scope).
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Interior Component Service:
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Instructions for removing and installing seats, dashboard components, door panels, and headliners.
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Technical Depth
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Depth:
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Comprehensive, covering routine maintenance to complete engine and transmission rebuilds. Includes detailed diagrams, torque specifications, and diagnostic procedures.
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Wiring Diagrams:
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Detailed electrical wiring diagrams for all major systems, crucial for diagnosing electrical faults.
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Torque Specifications:
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Comprehensive list of torque specifications for all critical fasteners, essential for proper assembly and preventing damage.
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Troubleshooting Charts:
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Inclusion of diagnostic flowcharts and symptom-based troubleshooting guides for common problems.
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Engine Specifications
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Primary Engine
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Gasoline Options 1985:
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M102 2.3L Inline-4 (e.g., 230E), M103 2.6L Inline-6 (e.g., 260E - less common in all markets for '85 W123, but some variants existed).
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Diesel Options 1985:
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OM615 2.0L Diesel Inline-4, OM616 2.4L Diesel Inline-4 (e.g., 240D), OM617 3.0L Diesel Inline-5 Turbocharged (e.g., 300D, 300TD).
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Engine Codes Examples:
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Gasoline: M102.980 (2.3L), Diesel: OM615.940 (2.0L), OM616.912 (2.4L), OM617.912 (3.0L Turbo).
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Performance
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Typical Horsepower Gasoline:
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2.3L: Approx. 130-136 hp; 2.6L: Approx. 160-168 hp.
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Typical Horsepower Diesel:
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2.0L: Approx. 70 hp; 2.4L: Approx. 72-77 hp; 3.0L Turbo: Approx. 115-123 hp.
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Fuel System
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Gasoline Injection Type:
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Bosch K-Jetronic (CIS - Continuous Injection System) mechanical fuel injection for most gasoline models.
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Diesel Injection Type:
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Bosch inline or distributor type fuel injection pumps.
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Maintenance
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Service Intervals
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Oil Change Interval:
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Typically every 7,500-10,000 miles (12,000-16,000 km) or annually, depending on driving conditions and oil used.
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Major Service Intervals:
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Includes spark plug replacement, fuel filter, air filter, and transmission fluid checks/changes at intervals often around 30,000-50,000 miles (48,000-80,000 km).
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Fluid Specifications
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Engine Oil Type:
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API SG or higher, SAE 10W-40 or 15W-40 recommended for most gasoline and diesel engines. Specific viscosities may vary by climate. Always consult the manual for precise recommendations.
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Coolant Type:
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Mercedes-Benz approved coolant concentrate mixed with distilled water. Typically a 50/50 mix. Refer to manual for specific MB Part Number.
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Transmission Fluid Auto:
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Dexron II or equivalent. Capacity approx. 1.5-2.0 liters for torque converter refill.
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Brake Fluid Type:
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DOT 3 or DOT 4 brake fluid.
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Power Steering Fluid:
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Mercedes-Benz approved power steering fluid or Dexron II/III automatic transmission fluid.
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Differential Fluid:
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Hypoid gear oil, SAE 80W-90 or SAE 85W-90 API GL-5.
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Known Issues
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Common W123 Issues:
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Vacuum system leaks (affecting door locks, central locking, climate control), rust (especially around wheel arches, sills, and battery tray), aging rubber hoses and mounts, potential diesel injector pump issues (OM617), headlight switch failures.
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Diesel Specific Maintenance:
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Glow plug system maintenance, regular fuel filter changes (critical for diesel engines), checking and cleaning air filters frequently.
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