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Mercedes OM642
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Mercedes OM642
Verdict
RISKY · 52/100
Est. cost /3yr
€4,000-9,000 over 3 years depending on mileage and whether the timing chain has already been addressed, covering routine maintenance, EGR and swirl flap work, and a possible one-off chain replacement
Oil interval
10,000 km
Recalls
1
Worst issue
Timing Chain Stretch and Tensioner Failure
CRITICAL
Mercedes OM642
W166 · W166
Timing Chain Stretch and Tensioner Failure
€1,500-4,000
CRITICAL
EGR Valve and EGR Cooler Failure
€600-2,000
HIGH
Intake Manifold Swirl Flap Motor Failure
€300-900
HIGH
Oil Leaks from Valve Cover Gasket and Oil Cooler
€400-1,200
MODERATE
Mercedes OM642
W166 · W166
•Cold-start the engine from fully cold and listen for any timing chain rattle in the first 5 seconds, walk away if heard
•OBD-II scan for all stored and pending fault codes, especially EGR, swirl flap, and camshaft position sensor codes
•Inspect the intake manifold area and underside of engine for oil leaks or soot deposits indicating EGR or cooler issues
•Request full service history and verify oil changes were done every 10,000 km or less with correct MB-approved low-SAPS oil
•Check coolant level and condition. Milky or low coolant can indicate EGR cooler failure or head gasket issues
•Ask specifically if timing chain, EGR valve, or swirl flap work has ever been carried out and request receipts
•Check the build date and emissions spec (Euro5 pre-2015 vs Euro6 2015 onward) to know which EGR and aftertreatment system the car uses
Mercedes OM642
W166 · W166
Timing Chain Kit (chain, tensioner, guide rails)
Inspect tensioner condition and listen for cold-start rattle. Replace proactively if any rattle detected or over 150,000 km.
150,000 km
EGR Valve and EGR Cooler
Clean or replace EGR valve at major service. Pressure-test EGR cooler for leaks.
120,000 km
Swirl Flap Actuator Motor
Inspect and test actuator operation. Consider swirl flap delete kit as preventive measure.
100,000 km
Mercedes OM642
W166 · W166
Fuel Injector Lines / Fuel Rail
Fuel injector line connections on some OM642-equipped Mercedes-Benz models were reported to develop micro-cracks over time, allowing fuel seepage near hot engine components and raising engine bay fire risk.
Mercedes OM642
W166 · W166
✓Strong torque output (620 Nm) for confident towing and highway cruising
✓Aluminium block and heads keep weight down for a V6 diesel
✓Wide model availability means good parts and specialist knowledge base
✓W166 platform is more refined and better built than predecessor W164
✓Long production run means many independent specialists are familiar with the engine
Mercedes OM642
W166 · W166
Real consumption
9.2 L/100km
Official consumption
Not available
Oil interval
10,000 km
Oil spec
MB 229.51 or 229.52 5W-30 fully synthetic low-SAPS
Est. cost /3yr
€4,000-9,000 over 3 years depending on mileage and whether the timing chain has already been addressed, covering routine maintenance, EGR and swirl flap work, and a possible one-off chain replacement
Mercedes OM642
W166 · W166
258 hp · 620 Nm
2011-2014
265 hp · 620 Nm
2015-2019
The hp difference between the two OM642 tunes in the W166 (258 hp vs 265 hp) is minor and not the deciding factor. The real distinction is emissions hardware: post-2015 Euro6 cars gain an AdBlue/SCR system with its own failure points (NOx sensors, dosing pump, tank heater) on top of the existing timing chain, EGR, and swirl flap risks. Earlier Euro5 cars are mechanically simpler but carry no update to the timing chain tensioner design, so chain risk is the same across both. Choose based on documented maintenance history and a clean cold-start and OBD check rather than the model year or power figure alone.