MajorCommonFluid Leaks

Mercedes-Benz GLS: X166 OM642 Oil Cooler Seal Leak in the Engine V (GL350 BlueTEC / GLS350d)

X166 OM642 Oil Cooler Seal Leak in the Engine V (GL350 BlueTEC / GLS350d) is a common fluid leaks fault on the Mercedes-Benz GLS on the 2013–2019 cars, and we rate it major. Putting it right costs $1,400 to $3,000 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 10 documented faults on the Mercedes-Benz GLS.

Vehicle: Mercedes-Benz GLS
Engine: 3.0L
Years: 2013–2019
Fuel: diesel
System: Fluid Leaks

This page covers the Mercedes-Benz GLS 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 GLS faults10 documented faults on this model

What you are looking at

No photograph available

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

What goes wrong

The OM642 V6 diesel oil cooler sits in the valley between the cylinder banks under the intake manifold, and its rubber seals harden and leak. This continues from the earlier X164 GL onto the X166 GL350 BlueTEC and GLS350d, even with the later purple Viton seals; Mercedes issued bulletin LI18.30-P-055434 for oil traces at the oil cooler in the inner V of engine 642, listed against the 2015 GL350. Oil pools in the V and runs down the back of the engine onto the transmission bell housing, and once it starts the leak tends to speed up. The seals are cheap but the intake manifold and turbo pipework must come off, so most of the cost is labour. Ignored, it can drop the oil level far enough to damage the engine.

What you would notice

'Check oil level' or low oil message
Oil level dropping between services
Oil drips under the back of the engine
Burning oil smell after a drive
Oil wetness at the rear of the engine and the bell housing

How to check it

Where to look. Centre of the engine between the two cylinder banks, under the intake manifold; leaks show at the rear of the engine and on the bell housing

Look under the car where it has been parked for oil spots below the rear of the engine.
Open the bonnet, lift off the plastic engine cover if it comes away easily, and use a phone torch to look down the back of the engine between the cylinder heads for wet oil or oily grime.
Check the oil level on the dash menu and ask how much it uses between services.
After the test drive, sniff for a hot oil smell.
Ask for invoices showing the oil cooler seals have been done, and when.
If a workshop inspection is possible: put the car on a hoist and look at the rear of the engine and the top of the transmission bell housing for oil running down from the V, which confirms the oil cooler seals rather than a rocker cover leak.

Parts involved: Intake manifold, Turbocharger.

What it costs to put right

$1,400 to $3,000 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 ever been replaced, and do you have the invoice?”
“Does it need oil topped up between services?”
“Has a low oil message ever come up?”

Now check the Mercedes-Benz GLS 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 TSB LI18.30-P-055434 'Traces of oil in area of oil cooler (inner V) on engine 642' (carcomplaints.com, 2015 GL350)
IDParts blog: Mercedes oil cooler seal leak on 3.0L V6 engines (lists GL350 BlueTEC to 2016)
IDParts: Oil Cooler Seal Kit (W166)(X166)(W221) part 6421880480

Mercedes-Benz GLS buyer questions

Is x166 om642 oil cooler seal leak in the engine v (gl350 bluetec / gls350d) serious on a Mercedes-Benz GLS?

We rate it major and common on the Mercedes-Benz GLS. The OM642 V6 diesel oil cooler sits in the valley between the cylinder banks under the intake manifold, and its rubber seals harden and leak. This continues from the earlier X164 GL onto the X166 GL350 BlueTEC and GLS350d, even with the later purple Viton seals; Mercedes issued bulletin LI18.30-P-055434 for oil traces at the oil cooler in the inner V of engine 642, listed against the 2015 GL350. Oil pools in the V and runs down the back of the engine onto the transmission bell housing, and once it starts the leak tends to speed up. The seals are cheap but the intake manifold and turbo pipework must come off, so most of the cost is labour. Ignored, it can drop the oil level far enough to damage the engine.

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

$1,400 to $3,000 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 GLS years are affected?

Our research records this fault on the 2013–2019 Mercedes-Benz GLS. 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 it has been parked for oil spots below the rear of the engine. Open the bonnet, lift off the plastic engine cover if it comes away easily, and use a phone torch to look down the back of the engine between the cylinder heads for wet oil or oily grime. Check the oil level on the dash menu and ask how much it uses between services. After the test drive, sniff for a hot oil smell. Ask for invoices showing the oil cooler seals have been done, and when. If a workshop inspection is possible: put the car on a hoist and look at the rear of the engine and the top of the transmission bell housing for oil running down from the V, which confirms the oil cooler seals rather than a rocker cover leak. Look here: Centre of the engine between the two cylinder banks, under the intake manifold; leaks show at the rear of the engine and on the bell housing