Mercedes-Benz GL X164

V6 diesel with common rail and piezo injectors. Powerful and refined. Known for blocked oil coolers, swirl flap failure and EGR problems. High mileages possible with good maintenance.

• !! Oil Cooler Gaskets Leaking — Oil and Coolant Loss from 120,000 km

  The best-known problem of the OM642: the oil cooler gaskets in the V-section of the engine fail. Oil leaks into the coolant or externally. Particularly prone on vehicles built up to 2009.

  Symptoms: Oil loss warning, oil spots under the left side of the vehicle, oil streaks visible on the belt tensioner
  800–2,500 $
  Ad oil cooler gasket OM642oil cooler OM642 3.0 CDIA6421800615 oil cooler
• !! Swirl Flap Linkage Breaks — Plastic Joint Fails from 100,000 km

  The plastic linkages of the swirl flaps in the OM642 intake manifold break. Aluminium repair kits are available and more durable. In the event of complete failure there is a risk of debris entering the engine.

  Symptoms: Engine warning light, fault codes for intake flap/swirl flap, power loss particularly at low rpm
  200–800 $
  Ad Drallklappe repairsatz OM642swirl flaps-repairsatz OM642 3.0 CDI6420907737 OM642 Ansaug
• !! Injector Seal Leaking — Soot Deposits and Diesel in Oil from 120,000 km

  Piezo injectors seal poorly from heat, diesel enters the engine oil. Oil loses lubrication properties, tar-like residue around injectors is the typical telltale sign.

  Symptoms: Rough idle, increased fuel consumption, knocking noises, oil level rising due to diesel contamination, engine oil smells of diesel
  300–900 $
  Ad fuel injector O-ring seal OM642 A6420170360Kupferdichtscheibe fuel injector CDIfuel injectorgasket OM642

+ 4 more engine weaknesses + vehicle weaknesses

Successor to the OM628, from 2005 with revised common rail injection at 1,600 bar and piezo injectors. Power output rose to up to 320 hp at 730 Nm — the gearbox hit its limits early, prompting Mercedes to recalibrate the NAG2 mapping during series production. Mechanically the OM629 shares most challenges with its predecessor but adds its own: the oil cooler in the V-area tends to leak at high mileages and additionally promotes EGR fouling of the intake tract. Cylinder heads come under extreme pressure during high-rpm full-load pulls — warped heads are not uncommon beyond 200,000 km. Piezo injectors demand clean fuel and short oil change intervals (10,000 km, 229.51 or 229.52). Anyone taking on this engine should budget for preventive oil cooler and seal replacement early on.

• !! Cylinder head warped -- coolant loss from 250,000 km

  Warped cylinder heads allow combustion gases into the cooling system. Overpressure constantly pushes coolant out through the expansion tank. Engine runs at temperature, coolant level drops steadily -- replacement costs 5,000-16,000 EUR.

  Symptoms: Coolant warning light despite stable engine temperature, coolant overflow from expansion tank, no visible external leak.
  5,000–16,000 $
  Ad cylinder head OM629 V8 CDIcylinder head gasket OM629 4.0replacementmotor OM629.9
• !! NAG2 transmission at torque limit from 120,000 km

  The NAG2 automatic transmission is rated for approximately 700 Nm; the OM629 delivers up to 730 Nm. Early build years without shift module adaptation showed driveshaft failures and gearbox problems. Later revised.

  Symptoms: Shift jerks, gearbox fault messages, missed shifts, vibration on pull-away.
  1,500–5,000 $
  Ad drive shaft E420 CDI W211NAG2 gearbox 7G-Tronic Revision
• !! Oil Cooler Leak in V-Section from 180,000 km

  The oil cooler sits at the lowest point in the V-section of the engine and seals with rubber gaskets. At high mileages oil seeps out, pools in the V and drips down. Repair takes approximately 2 days.

  Symptoms: Oil spots under the vehicle, oil mist in the V-section of the engine bay, elevated oil consumption.
  800–2,000 $
  Ad oil cooler OM629 V8 CDIoil coolergasket OM629 420 CDIseal kit oil cooler OM629

+ 3 more engine weaknesses + vehicle weaknesses

Large-displacement naturally aspirated V8, second generation with variable valve timing on all four camshafts. Technically related to the M272 V6 — shares its known balance shaft sprocket problem on build years before 2007 (engine number below 088611). From that number the sprocket was made of hardened steel. Check early engines for fault codes P0016/P0017 and cold-start chain noise. The 5.5-litre with 285 kW is the typical variant; the 5.0-litre with 225–250 kW is somewhat more forgiving in heavier vehicles. The M278 BiTurbo successor is more efficient and more powerful, but sounds considerably less characterful — the M273 is the last true naturally aspirated V8 from Stuttgart. Pre-purchase: always check for camshaft adjuster leaks (oil in wiring harness) and thermostat fault P0128. Oil changes every 10,000 km with MB 229.5.

• !! Balance shaft sprocket — same weakness as M272 from 140,000 km

  The M273 V8 shares the balance shaft sprocket issue with the M272 V6. The soft composite material of the sprocket wears down, causing timing chain rattle.

  Symptoms: Fault codes P0016/P0017, chain rattling, rough idle, power loss
  2,500–5,500 $
  Ad Ausgleichswelle M273 V8Ausgleichswellen-Umlenkrad M273Ausgleichswelle M273
• !! Camshaft Adjuster Leaking — Oil in Wiring Harness from 110,000 km

  As with the similarly-designed M272, the solenoid valves leak. The V8 has 4 per bank — consequential costs are particularly high due to more solenoids. Oil migrates by capillary action all the way to the ECU.

  Symptoms: Check engine light with camshaft fault codes P0014/P0015/P0021/P0025, lambda sensor failures, in extreme cases ECU failure
  200–2,000 $
  Ad Solenoid camshaft adjuster M273Centre valve M273 V8Oil stop cable V8 Mercedes
• !! Valve cover gaskets leaking on both sides from 130,000 km

  Like the M113, the valve cover gaskets on the M273 V8 become porous over time. With a V8 having two cylinder heads, the workload doubles.

  Symptoms: Oil spots under the vehicle, oil smell after hard driving, oily engine bay
  400–1,000 $
  Ad valve cover gasket M273 V8valve cover gasket M273Elring M273

+ 6 more engine weaknesses + vehicle weaknesses

Large-displacement naturally aspirated V8, second generation with variable valve timing on all four camshafts. Technically related to the M272 V6 — shares its known balance shaft sprocket problem on build years before 2007 (engine number below 088611). From that number the sprocket was made of hardened steel. Check early engines for fault codes P0016/P0017 and cold-start chain noise. The 5.5-litre with 285 kW is the typical variant; the 5.0-litre with 225–250 kW is somewhat more forgiving in heavier vehicles. The M278 BiTurbo successor is more efficient and more powerful, but sounds considerably less characterful — the M273 is the last true naturally aspirated V8 from Stuttgart. Pre-purchase: always check for camshaft adjuster leaks (oil in wiring harness) and thermostat fault P0128. Oil changes every 10,000 km with MB 229.5.

• !! Balance shaft sprocket — same weakness as M272 from 140,000 km

  The M273 V8 shares the balance shaft sprocket issue with the M272 V6. The soft composite material of the sprocket wears down, causing timing chain rattle.

  Symptoms: Fault codes P0016/P0017, chain rattling, rough idle, power loss
  2,500–5,500 $
  Ad Ausgleichswelle M273 V8Ausgleichswellen-Umlenkrad M273Ausgleichswelle M273
• !! Camshaft Adjuster Leaking — Oil in Wiring Harness from 110,000 km

  As with the similarly-designed M272, the solenoid valves leak. The V8 has 4 per bank — consequential costs are particularly high due to more solenoids. Oil migrates by capillary action all the way to the ECU.

  Symptoms: Check engine light with camshaft fault codes P0014/P0015/P0021/P0025, lambda sensor failures, in extreme cases ECU failure
  200–2,000 $
  Ad Solenoid camshaft adjuster M273Centre valve M273 V8Oil stop cable V8 Mercedes
• !! Valve cover gaskets leaking on both sides from 130,000 km

  Like the M113, the valve cover gaskets on the M273 V8 become porous over time. With a V8 having two cylinder heads, the workload doubles.

  Symptoms: Oil spots under the vehicle, oil smell after hard driving, oily engine bay
  400–1,000 $
  Ad valve cover gasket M273 V8valve cover gasket M273Elring M273

+ 6 more engine weaknesses + vehicle weaknesses