MajorCommonFluid Leaks

Mercedes-Benz S-Class: Oil cooler seal leaks and intake sludge/swirl-flap faults (OM642 3.0 V6 diesel, S320 CDI / S350 CDI / S350 BlueTEC)

Oil cooler seal leaks and intake sludge/swirl-flap faults (OM642 3.0 V6 diesel, S320 CDI / S350 CDI / S350 BlueTEC) is a common fluid leaks fault on the Mercedes-Benz S-Class on the 2006–2017 cars, and we rate it major. Putting it right costs $1,800 to $4,000 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 20 documented faults on the Mercedes-Benz S-Class.

Vehicle: Mercedes-Benz S-Class
Engine: 3.0L
Years: 2006–2017
Fuel: diesel
System: Fluid Leaks

This page covers the Mercedes-Benz S-Class as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mercedes-Benz S-Class faults20 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the Intake manifold yet. We would rather show none than show a picture of a different part.

What goes wrong

The OM642 V6 diesel used across the W221 (S320 CDI/S350 CDI) and into the W222 (S350 BlueTEC to 2017) has an infamous oil cooler seal failure: the seals sit in the hot valley of the V and degrade, leaking oil down the back of the engine. The cooler itself is cheap but it is buried under the intake and turbo plumbing, so it is an 8-10 hour labour job. While the manifolds are off, the oil-vapour-clogged swirl flaps and intake tracts need cleaning - a seized swirl-flap motor can blow fuses and set emissions faults. Purple/updated Viton seals fitted once are considered the permanent fix.

What you would notice

Oil leak appearing from the centre-rear of the engine V
Oil drips on the driveway
Burning oil smell after a run
Rough running or emissions faults from stuck swirl flaps

How to check it

Where to look. Oil cooler in the engine valley between the cylinder banks; intake manifolds either side

Look under the car after it has been parked overnight and check where the engine meets the gearbox for wet oil - valley leaks run down the back of the engine.
Ask specifically whether the oil cooler seals have been done (the invoice is a big, distinctive one).
Confirm intake/swirl flap cleaning was done at the same time.

Parts involved: Intake manifold.

What it costs to put right

$1,800 to $4,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Have the oil cooler seals been replaced with the updated ones, and is there an invoice?”
“Were the intake manifolds and swirl flaps cleaned at the same time?”

Now check the Mercedes-Benz S-Class you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

IDParts blog 'Mercedes Oil Cooler Seal Leak on 3.0L V6 Engines'
Atlantic Motorcar 'Mercedes Oil Cooler Seals, 642 Diesel Engine Cause And Correction'
MBWorld diesel forum 'OM642: New viton oil cooler seals still leaking'

Mercedes-Benz S-Class buyer questions

Is oil cooler seal leaks and intake sludge/swirl-flap faults (om642 3.0 v6 diesel, s320 cdi / s350 cdi / s350 bluetec) serious on a Mercedes-Benz S-Class?

We rate it major and common on the Mercedes-Benz S-Class. The OM642 V6 diesel used across the W221 (S320 CDI/S350 CDI) and into the W222 (S350 BlueTEC to 2017) has an infamous oil cooler seal failure: the seals sit in the hot valley of the V and degrade, leaking oil down the back of the engine. The cooler itself is cheap but it is buried under the intake and turbo plumbing, so it is an 8-10 hour labour job. While the manifolds are off, the oil-vapour-clogged swirl flaps and intake tracts need cleaning - a seized swirl-flap motor can blow fuses and set emissions faults. Purple/updated Viton seals fitted once are considered the permanent fix.

How much does it cost to fix on a Mercedes-Benz S-Class?

$1,800 to $4,000 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mercedes-Benz S-Class years are affected?

Our research records this fault on the 2006–2017 Mercedes-Benz S-Class. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Look under the car after it has been parked overnight and check where the engine meets the gearbox for wet oil - valley leaks run down the back of the engine. Ask specifically whether the oil cooler seals have been done (the invoice is a big, distinctive one). Confirm intake/swirl flap cleaning was done at the same time. Look here: Oil cooler in the engine valley between the cylinder banks; intake manifolds either side