Which Mercedes engine does this page cover?

The OM642 3.0 V6 diesel, used in Mercedes cars and in the Vito, Viano and Sprinter vans. If you are not sure which engine your car has, send us the registration and we will check.

Where is the oil cooler on the OM642?

It sits in the V between the two banks of cylinders, which is why oil from a leaking seal collects there.

Does the oil cooler itself need replacing?

Mercedes' own guidance for this leak says the cooler is not the cause and must not be replaced: the seals are renewed. We confirm the source before quoting.

Is there a recall for the OM642 oil cooler leak?

Whether a recall applies depends on the individual car, so check yours on the gov.uk vehicle recall checker.

Will I know the cost before you start?

Yes. After the inspection you get a written price and a promised time for your next update, and no work starts until you approve it in writing.

Mercedes OM642 oil cooler

OM642 V6 diesel oil cooler seal leaks

On the Mercedes OM642 3.0 V6 diesel, oil collecting in the V of the engine can come from the seals between the engine block and the oil cooler, but a leaking turbo inlet seal looks the same, so we rule that out first. Once the source is confirmed, we renew the oil cooler seals, and nothing is done until you have agreed a written price.

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Last updated 12 November 2026

Which Mercedes models are affected?

This page covers the OM642 3.0 V6 diesel. Mercedes fitted it to cars and to the Vito, Viano and Sprinter vans. Mercedes’ technical guidance on this leak was written for the Vito and Viano (639) and the Sprinter (906).

If you are not sure which engine your Mercedes has, put the registration in the enquiry form and we will check. For other Mercedes work, see our Mercedes specialist page.

What are the symptoms?

The signs to look for are:

oil collecting in the V of the engine, between the cylinder banks
oil drips at the back of the engine, where it meets the gearbox, or on the undertray
a low oil level message

When you book, tell us whether you have been topping up the oil, and roughly how often.

What causes it?

The leak comes from the seals between the engine block and the oil cooler.

Mercedes’ guidance is clear that the oil cooler itself is not the cause of this leak.

How do you confirm it is the oil cooler seals before fitting parts?

A leak in the V of the engine is not a diagnosis on its own. A leaking turbo inlet seal produces oil in the same place and looks the same. Before we quote, we:

inspect the V of the engine and trace where the oil is coming from
rule out the turbo inlet seal first
check the oil level and look for other leaks underneath

We then show you what we found, with photos, and send a written price. No part is fitted until you approve it in writing.

What does the repair involve?

We renew the seals between the block and the oil cooler. Following Mercedes’ guidance:

the coolant is drained before the parts are dismantled
no abrasives are used on the sealing faces
the oil cooler is not replaced, because it is not the cause

Once the work is done, we refill the coolant, check for leaks and verify the repair, including a road test where appropriate.

How long does an oil cooler seal repair take?

It depends on what the inspection finds, including whether the turbo inlet seal or another leak also needs attention.

Before any work starts, you get a written price and a promised time for your next update. If the car needs to stay with us, ask about a courtesy car when you book.

Is there a recall for this leak?

Whether a recall applies depends on the individual car, so check your registration on gov.uk. Recall work is done by the manufacturer’s network, not by us.

Reverie Autocare is an independent specialist and is not affiliated with or endorsed by Mercedes-Benz.

Our promise on every job

Written approval before any extra work
Photographic proof of what we find
A promised update time
No surprise invoice
A test drive and verification where appropriate

Our service centre

Where will my car be looked after?

At our centre at 57 Great North Road, Welwyn Garden City, built so that waiting for your car is not wasted time.

Seven ramps and an on-site MOT bay
Three customer waiting areas
A co-working space with Wi-Fi
A multi-faith prayer room and quiet room
Lavazza coffee
Customer parking

Questions people ask us

Which Mercedes engine does this page cover?: The OM642 3.0 V6 diesel, used in Mercedes cars and in the Vito, Viano and Sprinter vans. If you are not sure which engine your car has, send us the registration and we will check.
Where is the oil cooler on the OM642?: It sits in the V between the two banks of cylinders, which is why oil from a leaking seal collects there.
Does the oil cooler itself need replacing?: Mercedes' own guidance for this leak says the cooler is not the cause and must not be replaced: the seals are renewed. We confirm the source before quoting.
Is there a recall for the OM642 oil cooler leak?: Whether a recall applies depends on the individual car, so check yours on the gov.uk vehicle recall checker.
Will I know the cost before you start?: Yes. After the inspection you get a written price and a promised time for your next update, and no work starts until you approve it in writing.