OM642 Oil Leak

[Benbay001]

Hi, I appear to have the common OM642 oil cooler oil leak.

Can someone confirmt this is an engine oil cooler and not a gearbox one? The engine oil has barely dropped.

Thanks

[trevalvole]

Benbay001 said:

Can someone confirm this is an engine oil cooler and not a gearbox one?

I can't, but presumably engine oil would look different to gearbox fluid?

[Benbay001]

Well it looks like black engine oil but then i can only see it as droplets on the exhaust.

[Yazza54]

A droplet of hot oil goes a long way. It'll take a long time for that to make a dent in your oil level.

[trevalvole]

Does it have a separate gearbox cooler? As far as I'm aware my petrol M112 5G W203 has a combined radiator/gearbox cooler.

[Stegel]

On our S211 it started leaving a decent pool - hand sized - of oil to the rear nearside of the engine - being a diesel it’s black 1 minute after an oil change. There is a drain hole on the rear left of the vee, so oil escaping from the oil cooler seals drains down that corner of the engine and then finds its way over the undertray. I tackled it within a couple of weeks of it appearing, and despite the amount it was leaking it wasn’t really evident on the dipstick. The oil cooler remained flat so I just changed the seals, but I know some instances where a new cooler is needed as well due to it being distorted.

[carreauchompeur]

Mine had a leak in a similar location but it turned out to be somewhere around the turbo instead, which presents at a very similar location… get it looked at by a specialist.

[Subzero2003]

Benbay001 said:

Hi, I appear to have the common OM642 oil cooler oil leak.

Can someone confirmt this is an engine oil cooler and not a gearbox one? The engine oil has barely dropped.

Thanks

Yeah, really common fault, the engine oil cooler sits in the V between the banks and the seals degrade. Our E350d is a 2012 and already came from the factory with the upgraded Viton seals, but these still failed at 7-8 years old and started leaking. Cost over a £1000 for the job all in - about £980 of that was labour, £20 in parts. There's no way round it unfortunately.

The other thing is that the turbo sits at the top of the engine and at the back. The seal from the turbo to the air intake can become loose over time, and where the PCV plugs into the side of the intake, and leak oil down the back of the engine. Places have been known to diagnose this is a rear main seal leak, but it's normally always the turbo intake boot/seal or the oil cooler. Both should be replaced as a matter of course - think you can get both for around £25. A tell tale sign of these seals failing is old gunky oil residue on the wires that sit underneath the turbo intake. If you have that, you should definitely replace the seal - if the oil becomes too much, it gets into the electrics and blows the swirl flap motor (iirc) that sits underneath and you get an engine management light.

[Classy6]

The leak looks like it's coming from the gearbox bell housing as the engine has oil run-off channels that run from the middle of the V down to the middle of bell housing. Thus it is difficult to tell if the leak is from the V or actually if it's a rear main oil seal (if a typical leak from this area, they are quite uncommon to leak on 642's).

Typically as stated the red turbo inlet pipe seal is 90% of the time been incorrectly fitted or has swollen and never been replaced so will cause an oil leak, which can also damage the inlet port shutoff motor, too.

Further to this, the oil cooler seals can also leak due to age. All of which can replicate a leak from the gearbox bell housing. The best thing to do is replace the red turbo inlet pipe seal first, clean off as much as possible and then see if the leak worsens/is still there after 100 miles or so.

If you are stripping down to the middle of the V, it's definitely worth cleaning/replacing the manifolds to ensure they don't cause issues with carbon on the swirl flaps.