Mercedes-Benz SLC R172

Widely used Mercedes diesel with aluminium block and steel liner. High mileages possible but known for injector seal issues, timing chain stretch and EGR problems.

• !! Chain Tensioner Seal Leaking — Recall

  Over 100,000 vehicles recalled: the chain tensioner seal leaks, allowing engine oil to drip onto the exhaust system and potentially ignite.

  Symptoms: Dropping oil level, oil smell from engine bay, oily deposits under the vehicle, possible oil fire
  0–300 $
  Ad OM651 chain tensioner gasketMercedes OM651 chain tensioner gasketA6510500277
• !! Timing Chain Stretch (Simplex Chain) from 150,000 km

  The OM651 uses a simplex timing chain. With short-trip driving and overdue oil change intervals the chain stretches.

  Symptoms: Light rattling noise on cold start from the rear of the engine, no fault code stored
  1,200–3,000 $
  Ad timing chain OM651timing chain kit OM651A6510500077
• !! Piezo Injector Faults from 80,000 km

  Same Delphi piezo injector problems as in the DE18: 220 CDI and 250 CDI variants affected. Mercedes replaced them with solenoid injectors as part of a service action.

  Symptoms: Vibrations and rough running especially under acceleration, elevated fuel consumption
  1,500–3,500 $
  Ad Piezo-fuel injector OM651fuel injector OM651Delphi Piezo-fuel injector OM651

+ 3 more engine weaknesses + vehicle weaknesses

Four-valve V6 in two basic variants: 3.5L naturally aspirated (DES 35, 185–225 kW) with direct injection and stratified charge — refined, linear, no classic naturally aspirated feel. And the 3.0L BiTurbo family (DEH 30 LA, 245–295 kW) with Nanoslide coating, twin turbochargers and water-air charge air cooler. The BiTurbo sings sonorously from 2,500 rpm and screams at the top — exceptional for a V6. Weak points: timing chain wears early when oil change intervals are pushed. Oil cooler in the V-block doesn't seal forever. Camshaft solenoids leak. On the 3.5L stratified-charge variant add NOx sensor failures from short-trip use. Early DES 35 (2011–2013) had piston slap issues. The BiTurbo unit with Nanoslide is considered more robust. Maintained with short oil change intervals (10,000–12,000 km) the engine easily lasts beyond 200,000 km.

• !! Oil cooler leaking in the V-block from 120,000 km

  Known weak point: the oil cooler gasket in the V-block of the M276 ages and starts leaking. Repair is extremely labour-intensive because the engine must be partially disassembled — cost €1,700–3,800.

  Symptoms: Oil spots under the vehicle, rainbow sheen on wet road, dropping oil level, oil smell
  1,700–3,800 $
  Ad oil cooler M276A2761880080oil cooler gasket M276 V6
• !! Camshaft adjuster leaking — wiring harness contaminated from 100,000 km

  Known damage pattern on all newer Mercedes engines: solenoid valves leak, oil migrates into the wiring harness. First the lambda sensors die, then the ECU. Repair documented up to €1,970.

  Symptoms: Check engine light with camshaft fault code, lambda sensor failure, oil film on connectors, in extreme cases ECU failure
  300–1,970 $
  Ad solenoid valve camshaftnversteller M276Zentralventil M276 V6Öl-Stopp-Kabel GLE W166
• !! Piston slap (early 3.5L variants) from 150,000 km

  On early M276 DES 35 (build years 2011–2013) pistons can loosen due to cylinder bore wear. Knock noise on cold start, worst case engine damage.

  Symptoms: Clacking and knocking on cold start from the engine area, getting louder over time, rough idle when cold
  3,000–8,000 $
  Ad piston M276pisto kit M276 3.5LZylinderlaufbuchse M276 DES 35

+ 7 more engine weaknesses + vehicle weaknesses

Modern turbocharged four-cylinder with direct injection and piezo injectors. Successor to the M271. Less susceptible to timing chain issues. Good balance of power and economy.

• !! High-Pressure Pump Faulty or Noisy from 120,000 km

  The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.

  Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087
  800–2,200 $
  Ad high-pressure fuel pump M274Kraftstoff-high-pressure fuel pump W205Benzin-high-pressure fuel pump M274 Bosch
• !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km

  On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.

  Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure
  150–1,800 $
  Ad solenoid valve camshaftnversteller M274camshaftnverstellermagnet W205 GLCÖl-Stopp-Kabel M274
• !! Electric thermostat failure from 100,000 km

  Primary weak point of the M274: the electric thermostat sits deep in the engine block and is hard to reach. Replacement takes around 3 hours.

  Symptoms: Engine does not reach operating temperature or overheats, temperature fluctuations, fault codes P0597–P0599
  350–1,000 $
  Ad thermostat M274A2742000215coolantthermostat M274

+ 3 more engine weaknesses + vehicle weaknesses

Modern turbocharged four-cylinder with direct injection and piezo injectors. Successor to the M271. Less susceptible to timing chain issues. Good balance of power and economy.

• !! High-Pressure Pump Faulty or Noisy from 120,000 km

  The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.

  Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087
  800–2,200 $
  Ad high-pressure fuel pump M274Kraftstoff-high-pressure fuel pump W205Benzin-high-pressure fuel pump M274 Bosch
• !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km

  On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.

  Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure
  150–1,800 $
  Ad solenoid valve camshaftnversteller M274camshaftnverstellermagnet W205 GLCÖl-Stopp-Kabel M274
• !! Electric thermostat failure from 100,000 km

  Primary weak point of the M274: the electric thermostat sits deep in the engine block and is hard to reach. Replacement takes around 3 hours.

  Symptoms: Engine does not reach operating temperature or overheats, temperature fluctuations, fault codes P0597–P0599
  350–1,000 $
  Ad thermostat M274A2742000215coolantthermostat M274

+ 3 more engine weaknesses + vehicle weaknesses

Modern turbocharged four-cylinder with direct injection and piezo injectors. Successor to the M271. Less susceptible to timing chain issues. Good balance of power and economy.

• !! High-Pressure Pump Faulty or Noisy from 120,000 km

  The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.

  Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087
  800–2,200 $
  Ad high-pressure fuel pump M274Kraftstoff-high-pressure fuel pump W205Benzin-high-pressure fuel pump M274 Bosch
• !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km

  On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.

  Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure
  150–1,800 $
  Ad solenoid valve camshaftnversteller M274camshaftnverstellermagnet W205 GLCÖl-Stopp-Kabel M274
• !! Electric thermostat failure from 100,000 km

  Primary weak point of the M274: the electric thermostat sits deep in the engine block and is hard to reach. Replacement takes around 3 hours.

  Symptoms: Engine does not reach operating temperature or overheats, temperature fluctuations, fault codes P0597–P0599
  350–1,000 $
  Ad thermostat M274A2742000215coolantthermostat M274

+ 3 more engine weaknesses + vehicle weaknesses