Mercedes-Benz ML W164

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

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

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

6.2-litre naturally aspirated V8, hand-built in Affalterbach to the 'One Man, One Engine' principle. 457–525 hp without any forced induction, rev limit at 7,200 rpm. The sound defines an era: a deep, bass-heavy rumble at 3,000 rpm, a scream above 5,000 that recalls American V8 racing engines. Throttle response is immediate — no turbo lag, no hesitation, every throttle command is executed instantly. Critical issue number one: camshafts wear out through inadequate cold-start lubrication with the factory 0W-40 oil. Switch to Ravenol 5W-40 RCS, let the engine idle for 10 seconds after a cold start, stay below 3,000 rpm until fully warm. Head bolt corrosion on engine numbers below 060658 (up to approx. 2010) — check without fail. Star Technical Bulletin 05.20/20b documents the tappet problem officially. Parts availability is becoming increasingly difficult — hydraulic tappets A1560500225 sometimes not available for months. Maintain the M156 properly and you have one of the most emotional V8s of the last 30 years.

• !! Head Bolt Corrosion — Coolant in Combustion Chamber from 50,000 km

  All M156 up to engine number 060658 affected: head bolts corrode through coolant contact at the bolt head, in worst case break off. Coolant enters the combustion chamber — engine damage. Mercedes fitted improved bolts from approx. 2010 (20x A1560160769 + 4x N000000005754, approx. 108 EUR net). Preventive replacement strongly recommended.

  Symptoms: Coolant loss without visible leak, white smoke from exhaust, oil-coolant mixture, check engine light, misfires on individual cylinders.
  1,500–8,000 $
  Ad Head bolt M156A1560160769 head boltN000000005754
• !! Camshaft Wear — Cold-Start Lubrication Deficit from 60,000 km

  Main problem of the M156: the factory 0W-40 oil drains from the camshafts at standstill; at cold start the lobes run briefly dry. Wear deteriorates exponentially. Camshaft regrinding (TechnoCam and others) as a cheaper alternative to new parts — 50% saving. Always replace the 32 hydraulic tappets (INA A1560500225) at the same time.

  Symptoms: Metallic ticking on cold start that disappears after 30–60 seconds, rough idle, power loss in the upper rev range. Remove valve cover and check lobe tips for wear.
  2,000–6,000 $
  Ad Camshaft M156A1560504301 inlet camshaftA1560500225 hydraulic tappet INACamshaft regrind M156
• !! Camshaft Adjuster — Locking Plate Wears Out from 70,000 km

  The fit of the locking plate in the camshaft adjuster widens over time — the adjuster slips, timing shifts. Clattering on cold start is the first symptom. Reinforced locking plates (300–1,000 EUR for 4 pieces) as a permanent solution. Bearing cap torque 10 Nm, adjuster 45 Nm + 90°.

  Symptoms: Rattling/clattering on cold start for 2–10 seconds, disappears after oil pressure build-up. With advanced wear: also audible when warm, rough idle, shifted timing, power loss.
  800–3,000 $
  Ad Camshaft adjuster M156Locking plate M156 reinforcedCamshaft adjuster repair kit AMG

+ 7 more engine weaknesses + vehicle weaknesses

Four-valve V6 with variable valve timing. Smooth and powerful. Known for balance shaft wear (revision sprocket) on early build years. Balance shaft gear problem addressed by Mercedes with a recall.

• !! Balance Shaft Sprocket Wears Prematurely from 140,000 km

  The plastic balance shaft sprocket on the M272 wears prematurely from the timing chain. The right cylinder bank goes out of timing. Affected up to end of October 2006.

  Symptoms: Fault codes P0016/P0017 (camshaft right bank), chain rattling, rough running at idle, in extreme cases engine damage
  2,500–5,500 $
  Ad Balance shaft M272Balance shaft sprocket M272 V6A2720500747 balance shaft sprocket
• !! Timing Chain Stretches and Damages Timing from 120,000 km

  Alongside the balance shaft issue the M272 shows premature timing chain stretch. Chain wear on softer sprockets leads to timing deviations.

  Symptoms: Chain noise especially on cold start, camshaft fault codes, rough running, engine irregularities
  2,000–4,000 $
  Ad Timing chain M272 V6Timing chain kit M272Chain guide M272
• !! Camshaft Adjuster Leaks — Wiring Harness Contaminated from 90,000 km

  Four camshaft adjuster solenoids (two per cylinder bank) develop leaks; oil creeps into the wiring harness as far as the ECU. Repair costs up to €1,700 documented.

  Symptoms: CEL, oil traces at camshaft connectors, lambda sensor failure due to oil contamination, non-specific faults that recur
  100–1,700 $
  Ad solenoid valve camshaftnversteller M272Zentralventil M272 A2720500578Zentralventil A2720500478

+ 3 more engine weaknesses + vehicle weaknesses

Naturally aspirated V8 in three displacements from 4.3 to 5.5 litres — old-school character with no turbo lag. Linear power delivery, deep rumble from 2,000 rpm building to a hoarse roar above 5,000. Peak torque at 3,000; beyond that it thins out — yet it's silky in part-throttle and surprisingly economical. Achilles heel is the seals: rear crankshaft oil seal practically universal above 150,000 km (gearbox removal required, 600–900 EUR), valve covers and oil filter housing seep with age. All cheap parts. The one critical point: the rubber damper on the crankshaft pulley hardens with age — when it fails the pulley machines into the sump. Replace preventively every 150,000 km. Oil changes every 10,000 km with 5W-40, 16 spark plugs every 60,000–80,000 km — then 400,000 km is realistic.

• !! Vibration Damper/Pulley — Rubber Hardens from 170,000 km

  The rubber damper in the crankshaft pulley hardens with age and can eat into the sump — catastrophic consequential damage. Preventive replacement every 150,000 km strongly recommended.

  Symptoms: Unusual vibrations at idle, in worst case metallic scraping from below. Often no prior warning — sudden failure.
  400–2,000 $
  Ad Vibration damper pulley M113Crankshaft pulley rubber damper M112 M113
• !! Rear Crankshaft Seal Leaking from 150,000 km

  The rear crankshaft seal is leaking on virtually all M113 engines above 150,000 km. Gearbox removal required — 600–900 EUR workshop costs. If oil creeps into the torque converter it becomes expensive.

  Symptoms: Oil drops or oil film visible at the engine-gearbox interface, oil loss without any other apparent leak on the engine.
  600–900 $
  Ad A1129970246 crankshaft seal M113Crankshaft seal M113 rear
• !! Engine Mounts Worn Prematurely from 90,000 km

  Engine mounts can fail before 100,000 km. Practical test: finger between the stabiliser bar and front sump — no clearance means the mount is dead. Not visually checkable without removal.

  Symptoms: Vibrations in interior especially at idle, dull rumbling on acceleration, in worst case contact between engine and bodywork.
  200–500 $
  Ad Engine mount M113 W211Engine mount M113 W220

+ 7 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