Market Position:
The Mercedes-Benz W123 series, particularly the 300 TD Turbo diesel variants, represented Mercedes-Benz's commitment to robust, reliable, and comfortable luxury touring sedans and estates. These models were positioned as premium vehicles known for their durability and engineering prowess.
Competitive Analysis:
In its era, the W123 competed with other premium European manufacturers like BMW (e.g., 5 Series), Audi, and other luxury marques, often differentiated by its build quality, diesel engine efficiency and longevity, and ride comfort.
Key Features:
The 300 TD Turbo (often referred to by its OM617.912 engine code) was known for its torquey turbocharged diesel engine, offering a blend of performance and fuel economy for its time. Its legendary build quality, comfortable ride, and luxurious interior made it a sought-after vehicle.
Engine System:
Engine oil and filter change, valve clearance adjustment and checking, idle speed adjustment, injection timing adjustment and checking, fuel filter replacement, air filter cleaning and replacement, V-belt tension check, poly V-belt inspection, manifold seating, oxygen sensor replacement (if applicable to the turbo diesel model of this era), spark plug check/replacement (though typically diesel glow plugs are relevant), coolant level/antifreeze check, cooling system inspection and fluid replacement, engine stop adjustment, engine mount bolt retorque.
Transmission System:
Manual transmission oil change and level check/correction, automatic transmission fluid and filter change, automatic transmission fluid level check/correction, transfer case fluid change and level check/correction.
Drivetrain System:
Clutch disk wear inspection, clutch system fluid level check/correction and inspection, front axle oil level check/correction, front axle ball joint inspection, rear axle oil change and level check/correction, rear axle mount limiting stop adjustment, drive shaft flexible coupling inspection.
Brakes System:
Brake fluid level check, brake line inspection, brake pad and disk thickness check, brake disk inspection and cleaning, parking brake cable inspection and adjustment, brake fluid replacement, parking brake test.
Suspension Steering System
Suspension Steering:
Suspension and body structure inspection, steering play check, steering bolt tightening, power steering fluid level check, level control, ADS, 4MATIC fluid level check (note: 4MATIC typically introduced later, may be specific to certain late W123 variants or a general Mercedes system coverage), self-leveling suspension inspection.
Body Chassis Electrical:
Water leakage and corrosion inspection, wheel inspection and rotation, tire inspection and pressure correction, wheel bolt tightening, battery fluid level check, warning and indicator lamp check, 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, safety belt inspection, backrest lock operation check, lower noise encapsulation panel removal/installation, body paint damage inspection.
Maintenance Procedures:
Routine maintenance tasks such as oil changes, filter replacements, fluid level checks, belt adjustments, and lubrication points.
Repair Procedures:
Detailed step-by-step instructions for component replacement and repair, including engine, transmission, brakes, suspension, and electrical systems.
Troubleshooting Diagnostics:
Implied through the coverage of various checks and inspections, and the 'dealer-level' information.
Technical Depth:
Comprehensive, covering factory-level diagnostic and repair procedures. Includes adjustment specifications and component inspections, indicating a high level of technical detail suitable for professional mechanics and serious DIY enthusiasts.
Engine Type:
Inline 5-cylinder turbocharged diesel
Displacement:
3.0 Liters (2998 cc)
Horsepower:
Approximately 125 hp @ 4350 rpm (figures may vary slightly by market/spec).
Torque:
Approximately 184 lb-ft (250 Nm) @ 2400 rpm (figures may vary).
Fuel System:
Bosch inline injection pump with turbocharging. Diesel fuel.
Coolant Capacity:
Approximately 9.5 Liters (check specific year/model).
Oil Capacity:
Approximately 6.5 Liters (with filter change).
Recommended Oil Type:
API CD or higher, viscosity grade typically 15W-40 or 20W-50 depending on climate. Check manual for exact specifications.
Injection Timing:
Critical for performance and emissions. Typically specified in degrees BTDC (Before Top Dead Center) at a specific RPM and cylinder. Precise adjustment requires a dial indicator or timing light.
Standard Transmission:
4-speed manual transmission was standard on some models, but the 300 TD Turbo often came with a 4-speed automatic as standard or a popular option.
Optional Transmission:
4-speed automatic transmission (e.g., 722.118) was very common.
Automatic Transmission Fluid:
MB 236.1 or equivalent. Dexron II may be acceptable as a substitute by some sources, but MB spec is preferred.
Manual Transmission Oil:
API GL-4 or GL-5 gear oil. Viscosity typically 75W-90 or 80W-90. Check manual for specific MB spec.
Safety Ratings:
Official crash test data from this era is less standardized than today. However, the W123 was renowned for its robust build quality and engineered crumple zones, contributing to occupant safety.
Active Features:
Four-wheel disc brakes (front solid, rear solid or ventilated depending on model/year), power assisted steering.
Passive Features:
Reinforced chassis, safety-padded dashboard, laminated windshield, side-impact protection beams (in doors).
Infotainment Features:
Basic for the era: AM/FM radio, often with cassette player. Manual mentions 'cleaning cassette deck tone head'.
Driver Assistance:
Limited by modern standards. Key features include power steering and ABS (Anti-lock Braking System) on some later models. Manual mentions 'ADS, 4MATIC' which might indicate coverage for models equipped with these advanced (for the time) systems, though 4MATIC was a later addition to the W123 platform or introduced on subsequent models.
Climate Control Features:
Manual and automatic climate control systems were available. Manual covers 'heating & ventilation', 'dust filter', and 'recirculating air filter'.
Oil Change Interval:
Typically every 5,000-7,500 miles (8,000-12,000 km) or 6-12 months, but consult the manual for the most precise recommendation for this engine.
Fuel Filter Interval:
Recommended replacement every 15,000-30,000 miles (24,000-48,000 km), or as needed if experiencing issues. Crucial for diesel engine health.
Air Filter Interval:
Inspection every oil change, replacement typically every 15,000-30,000 miles (24,000-48,000 km).
Coolant Type:
Mercedes-Benz Specification 325.0 (Ethylene Glycol based antifreeze).
Brake Fluid Type:
DOT 3 or DOT 4 brake fluid.
Known Issues:
Potential for vacuum leak issues affecting central locking and HVAC, injector pump seal leaks, valve stem seal wear, rust (especially around wheel arches, door bottoms, and sunroofs), aging rubber components (hoses, mounts), and potential for head gasket issues if overheated. The OM617 engine itself is known for its robustness and longevity.
Brand Heritage:
Mercedes-Benz has a long history of engineering excellence, particularly in diesel engine technology and luxury vehicle manufacturing, dating back to the late 19th century.
Model Evolution:
The W123 series, produced from 1976 to 1986, replaced the W114/W115 series. The 300 TD Turbo was a key evolution, offering significantly improved performance over its naturally aspirated diesel predecessors, making diesel Mercedes more appealing for everyday driving.
Production Years:
W123 series: 1976-1986. 300 TD Turbo specific models within this range cover the years 1981-1985 as per the manual.
Manufacturing Location:
Germany (primarily Bremen and Stuttgart).
