Mercedes OM642 Rebuild, common faults & everything you need to know
A complete guide to Mercedes' 3.0-litre diesel V6 - a common-rail six in a 72-degree V configuration with DOHC per cylinder bank (four camshafts in total), 24 valves and a single variable-geometry turbo. Fitted to everything from the E-Class and ML/GLE to the G-Class, Sprinter and (through Mercedes engine supply) the Jeep Grand Cherokee. From the timing chain, oil cooler seal and injectors to power builds, with workshop prices and clear common-fault guides.
- VIN verification before delivery
- Delivery time normally approx. 1 week
- 12 month warranty on the engine
Robert has built and reconditioned German turbodiesels for over 30 years, and that is the experience we build on. The OM642 is Mercedes' V6 diesel, fitted to everything from the E-Class and ML/GLE to the S-Class, G-Class and Sprinter - and which Mercedes also supplied to the Jeep Grand Cherokee (WK, 2005-2010) and the Chrysler 300C CRD. It is an unusual 72-degree V6 with DOHC on each cylinder bank (four camshafts in total), 24 valves and a single variable-geometry turbo - the OM642 is never available in a factory-built biturbo configuration, unlike what some sources claim (the 420/450 CDI biturbo designation belongs to the separate OM629 V8 diesel). Early engines (up to around 2014) have cast iron cylinder liners, later engines a sprayed Nanoslide coating directly in the bores - a significant difference for any potential reboring. The timing chain sits at the rear, with separate chains to each bank. We handle everything from cylinder head reconditioning and turbo reconditioning to complete engine reconditioning with our own machine shop and a 12-month warranty.
The OM642 at a glance
Shared base data for the OM642 family. Variant-specific power and torque figures are listed in the table below, cross-verified against at least two independent sources per value. OEM part numbers for the separate left/right intake and exhaust camshafts confirm the true DOHC-per-bank design (four camshafts in total) - a detail that is often described incorrectly as "one camshaft per bank" in other compilations.
| Power | Torque | Typical example | From year |
|---|---|---|---|
| 135 kW (184 hk) | 400 Nm | G 280/300 CDI | 2005 |
| 140 kW (190 hk) | 440 Nm | Sprinter / Vito | 2007 |
| 165 kW (224 hk) | 540 Nm | ML 350 CDI, GLK 350 CDI | 2009 |
| 173 kW (235 hk) | 540 Nm | S 350 CDI/BlueTEC | 2005 |
| 195 kW (265 hk) | 620 Nm | E 350 BlueTEC, GL 350 BlueTEC, GLE | 2011 |
The power and torque figures above are identity data (the engine's output, not tightening torque), cross-verified against Wikipedia, mercedesclub.cz and independent spec databases. We show power/torque/model rather than the factory's internal suffix codes (e.g. OM642.930), because several independent sources contradict each other on exactly which code belongs to which model year - contact us with your chassis number if you need the exact code.
Torque specs
We only publish torque specs we have been able to verify against an actual factory page. For the OM642 we have not yet completed that verification against the Mercedes factory manual (WIS). We never guess and never borrow another engine's values. If you need tightening torques for a job of your own, get in touch and we will find them in the correct factory manual before your job begins.
Common faults on the Mercedes OM642
This is what we see most often when an OM642 comes in. Symptoms, causes and how we fix it.
Oil cooler seal - leak in the engine's valley
Common, can cause bearing damage • Critical- Symptoms
- An oil leak from a drain hole on the left rear of the block, a smell of oil, and in time a risk of low oil pressure if the leak is large. A metallic knocking noise - often from the front main bearing - can appear as a secondary result of oil starvation.
- Cause
- The oil/coolant heat exchanger sits between the two cylinder banks and is sealed with rubber O-rings that harden and shrink with heat cycling. A large share of what looks like main bearing failure on the OM642 actually traces back to oil starvation caused by this very leak rather than a primary bearing fault. The job is extensive - the turbo, intake manifold and EGR cooler have to come off to reach the oil cooler.
Injectors - copper washer leak ("Black Death")
Very common • High- Symptoms
- A smell of diesel, hard starting and a hard, jet-black layer of soot that builds up around and on top of the injector in the cylinder head.
- Cause
- The copper washer that seals the injector against the cylinder head loses its preload, which lets hot combustion gases leak past the injector and quickly carbonise into a hard layer of soot. Left untreated, the soot can literally cement the injector into the cylinder head, requiring a puller and boring tools to free it without damage. We test, reseal and replace injectors as needed.
Timing chain, guide rails & tensioner
High mileage • High- Symptoms
- A rattling noise, especially on cold start. Because the OM642 is an interference engine, a chain failure bends valves.
- Cause
- The main chain stretches over time and the hydraulic tensioner compensates until the guide rails wear or crack, after which tension can no longer be maintained. The chain system sits at the rear against the gearbox. We replace the entire chain kit with rails, tensioner and sprockets in one go.
Swirl flaps & linkage
Common • Medium- Symptoms
- Power loss, limp mode and fault codes for the intake flaps. In the worst case a broken-off flap part is drawn into a cylinder.
- Cause
- The electrically operated swirl flaps clog up with crankcase gases and EGR exhaust until the flap motor binds and eventually burns out. The brittle plastic link rods can also snap on their own. A secondary cause is an oil leak from the turbo's intake seal running straight down onto the flap motor, short-circuiting it. We replace or blank off the flaps properly.
EGR cooler & turbo actuator
High mileage • Medium- Symptoms
- Coolant loss with no visible external leak and white smoke (EGR cooler), or lost boost and over/underboost codes (turbo actuator).
- Cause
- The EGR cooler's passages crack from thermal cycling between hot exhaust and coolant. On the turbo the variable vanes can seize up with soot, and the drive gear in the electric actuator can wear until the control slips - two separate causes of failure that are often confused during diagnosis. We check and replace components in connection with larger engine work.
Mercedes OM642 rebuild prices
The OM642 is a V6 with two separate cylinder heads (one per cylinder bank). The cylinder head price below is per cylinder head - get in touch for a combined quote if both need work. We do cylinder boring, crankshaft grinding and cylinder head resurfacing with our own machine shop. The timing chain and turbo are handled separately. All prices exclude VAT and parts.
Cylinder head reconditioning
Bottom end
Full rebuild
Performance
The V6 design makes the price more inspection-dependent than usual. With two separate cylinder heads, four camshafts and an oil cooler deep in the engine's valley, the scope of work varies more between individual OM642s than on an inline engine. We always give a firm quote after inspection - call us or get a quote for an exact price for your specific engine.
Tuning the Mercedes OM642
The OM642 has high compression (18.0:1) and a robust aluminium block, which makes it a good base for torque gains through remapping. The timing chain, oil cooler seal and injectors must be kept in good order before any power increase.
- 1
Remap & exhaust
A Stage 1 remap and a freer exhaust system give a noticeable increase in torque. The bottom end handles this well with a healthy timing chain and tight oil cooler seals.
280-290 hk - 2
Upgraded injectors & Stage 2
Injectors in good condition and a Stage 2 remap take more out of the turbo system's margin. A healthy turbo is a prerequisite.
300-320 hk - 3
Turbo upgrade
An upgraded charge system together with a reinforced fuel system. Read more about turbo upgrades.
320+ hk - 4
Full build
A balanced bottom end and ported cylinder heads for those who want to maximise an already high-compression V6 diesel. We build the chain mainly in-house with performance engine building.
Contact us
Need a whole engine?
Sometimes the damage is too extensive for a rebuild to be worth it, or the car simply needs to be back on the road as fast as possible. That is when a ready-made replacement engine is the right way to go. Our replacement range includes reconditioned Mercedes OM642-engines, quality assured to Meksta's standard and checked at our workshop before delivery, with a 12-month warranty and no mileage limit. Since the same engine code often covers several generations, we always verify against your chassis number before the build is ordered.
Questions & answers about the Mercedes OM642
The questions we hear most often from OM642 owners.
What does it cost to rebuild a Mercedes OM642?
A cylinder head reconditioning costs about 7,500 - 10,500 SEK per cylinder head (the V6 has two), a complete engine reconditioning (both cylinder heads, bottom end and balancing) about 28,500 - 43,500 SEK. Because the OM642 has two cylinder heads and an oil cooler deep in the engine's valley, the scope of work varies more between individual engines than on an inline engine - we always give a firm quote after inspection.
Does the Mercedes OM642 have a biturbo?
No. The OM642 is always charged by a single variable-geometry turbo (VNT), at every power level. The biturbo designation and the names 420 CDI/450 CDI belong to a completely different, larger Mercedes diesel engine - the OM629 V8 - which is often confused online. If you see "OM642 biturbo" mentioned anywhere, it is most likely a mix-up with the OM629.
Is the Mercedes OM642 an interference engine?
Yes. If the timing chain jumps or snaps, the valves hit the pistons, causing bent valves and often major engine damage.
Which cars have the Mercedes OM642?
The OM642 is fitted to the E-Class, CLK/CLS, S-Class, ML/GLE, GL/GLS, GLK/GLC, R-Class, G-Class, Vito/Viano and Sprinter. Mercedes also supplied the engine to the Jeep Grand Cherokee (first-generation WK/WH, 2005-2010 - not the later WK2 generation) and to the Chrysler 300C CRD in Europe.
Can you tune an OM642?
Yes. A Stage 1 remap often gives a noticeable torque increase thanks to the high compression. With upgraded injectors, Stage 2 and a possible turbo upgrade you build on from there. A healthy timing chain, tight oil cooler seals and injectors in good order are a prerequisite before tuning.
See also: we recondition and build turbo engines and diesels from Mercedes and other manufacturers. Feel free to compare with Mercedes' smaller four-cylinder diesel Mercedes OM651 or BMW's inline six-cylinder diesel BMW N57. If you only need the turbo sorted, we do that via our turbo reconditioning. See all our engine types. Would you rather have a finished, reconditioned engine straight away? Buy a Mercedes OM642 exchange engine in the shop.
Have an OM642 that needs looking at?
Call us directly or send in a quote request. We reply within 24 hours.
Other engines we recondition
We recondition more engines than we have time to write guides about. Here are more that we see often.