MajorCommonFluid Leaks

Mercedes-Benz C-Class: Oil cooler seal leak in the engine V (3.0 OM642 V6 diesel)

Oil cooler seal leak in the engine V (3.0 OM642 V6 diesel) is a common fluid leaks fault on the Mercedes-Benz C-Class on the 2007–2014 cars, and we rate it major. Putting it right costs $1,500 to $3,500 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 45 documented faults on the Mercedes-Benz C-Class.

Vehicle: Mercedes-Benz C-Class
Engine: 3.0L
Years: 2007–2014
Fuel: diesel
System: Fluid Leaks

This page covers the Mercedes-Benz C-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 C-Class faults45 documented faults on this model

What you are looking at

No photograph available

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

What goes wrong

An oil cooler seal leak is a known issue on the 3.0 OM642 V6 diesel, as fitted to the W204 C 320 CDI and C 350 CDI. The oil cooler sits in the V between the cylinder banks, and its original seals harden with heat and leak oil, which runs to the back of the engine and drips from the bell housing. Engines built before about 2010 are most affected; Mercedes-Benz changed to Viton seals and issued service bulletin LI18.30-P-055434, but later engines can still leak. The repair is labour heavy because the intake and turbo plumbing has to come off.

What you would notice

Check oil level or oil level low warning
Oil level dropping between services
Oil drips or stains under the back of the engine
Burning oil smell

How to check it

Where to look. Engine V between the cylinder banks; oil runs to the rear of the engine and bell housing

Look under the car where the engine meets the gearbox for wet oil or drips, and check the under tray for pooled oil.
Check the oil level and ask whether the car has needed oil top ups.
Ask for invoices showing the oil cooler seals were replaced with Viton seals.
If a workshop inspection is possible: remove the bell housing inspection cover on a hoist and look for oil coming from the engine V.

Parts involved: Turbocharger.

What it costs to put right

$1,500 to $3,500 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, and do you have the invoice?”
“Does the car use or leak oil between services?”
“Has an oil level warning ever come on?”

Now check the Mercedes-Benz C-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.

Mercedes-Benz C-Class buyer questions

Is oil cooler seal leak in the engine v (3.0 om642 v6 diesel) serious on a Mercedes-Benz C-Class?

We rate it major and common on the Mercedes-Benz C-Class. An oil cooler seal leak is a known issue on the 3.0 OM642 V6 diesel, as fitted to the W204 C 320 CDI and C 350 CDI. The oil cooler sits in the V between the cylinder banks, and its original seals harden with heat and leak oil, which runs to the back of the engine and drips from the bell housing. Engines built before about 2010 are most affected; Mercedes-Benz changed to Viton seals and issued service bulletin LI18.30-P-055434, but later engines can still leak. The repair is labour heavy because the intake and turbo plumbing has to come off.

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

$1,500 to $3,500 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 C-Class years are affected?

Our research records this fault on the 2007–2014 Mercedes-Benz C-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 where the engine meets the gearbox for wet oil or drips, and check the under tray for pooled oil. Check the oil level and ask whether the car has needed oil top ups. Ask for invoices showing the oil cooler seals were replaced with Viton seals. If a workshop inspection is possible: remove the bell housing inspection cover on a hoist and look for oil coming from the engine V. Look here: Engine V between the cylinder banks; oil runs to the rear of the engine and bell housing