JHZR2
Staff member
I know I have a lot of threads about my 2008 ML320 lately. But this is an interesting one for a different reason. The front of my engine was kind of oily. I have a thread about the belt, other threads on brakes, PCV, etc. but I have been trying to figure out why the front of the engine was oily. The intake manifold connects up there, as does the intercooler in/out connections.
Diesels have blowby, and tend to have oil in the intake when the breather system is looped back into it. But two things bugged me. One was a turbo that I considered to be louder than I had expected for the engine, and the second was the oil that I saw on the front of the engine. I could tell that the oil was coming from someplace in the intake system, but it was very difficult to tell where. When I first got the vehicle, I replaced a few of the most well-known culprits for leaks. Everything seemed OK in terms of the quality of the seals I removed, but who knows. The wetness didn’t stop so I decided to pull the entire intake trunk off.
this unit connects the output of the intercooler together with the left and right bank of the intake, manifold, and blends in the EGR.
The oil wasn’t coming from the intake at the engine. I could tell that from looking at what was the most wet. I also knew that there was a lot of oil residue at my alternator, which was very concerning. I knew it had to be from over there.
Perhaps from the oil leak intake air temperature sensor?
Or maybe someplace else? So I decided to take apart all of the sections of the intake to replace the internal seals.
That red seal was not there when I pulled the two halves apart! Sure, there’s a meeting surface that is pretty smooth and pretty flat, and bolted together in four spots. But it was not enough to prevent all of the leakage of turbo boost, and the oil vapor that was with it.
The turbo is never that oily.
But enough pressurized mist was coming out to make a big mess.
I guess it was good to renew the PCV system regardless. But it’s just incredible to me that all of this was due to somebody at the dealership being careless when they were working on the car.
I’m also a little bit surprised that given the seepage and what must have been loss of boost, that no check engine lights were ever set off, and that I could still get over 26 mpg.
I do have to wonder if I will see a decent economy improvement given the efficiency increase of at least the turbo. I guess what was really happening was the loss of boost behaved kind of like a stuck open waist gate. And given that his engine makes plenty of power for my needs, And that I don’t really drive it high boost very often, perhaps the turbo just had enough overhead to provide what was needed.
Knocking on wood, that things will stay nice and dry for a while!
Diesels have blowby, and tend to have oil in the intake when the breather system is looped back into it. But two things bugged me. One was a turbo that I considered to be louder than I had expected for the engine, and the second was the oil that I saw on the front of the engine. I could tell that the oil was coming from someplace in the intake system, but it was very difficult to tell where. When I first got the vehicle, I replaced a few of the most well-known culprits for leaks. Everything seemed OK in terms of the quality of the seals I removed, but who knows. The wetness didn’t stop so I decided to pull the entire intake trunk off.
this unit connects the output of the intercooler together with the left and right bank of the intake, manifold, and blends in the EGR.
The oil wasn’t coming from the intake at the engine. I could tell that from looking at what was the most wet. I also knew that there was a lot of oil residue at my alternator, which was very concerning. I knew it had to be from over there.
Perhaps from the oil leak intake air temperature sensor?
Or maybe someplace else? So I decided to take apart all of the sections of the intake to replace the internal seals.
That red seal was not there when I pulled the two halves apart! Sure, there’s a meeting surface that is pretty smooth and pretty flat, and bolted together in four spots. But it was not enough to prevent all of the leakage of turbo boost, and the oil vapor that was with it.
The turbo is never that oily.
But enough pressurized mist was coming out to make a big mess.
I guess it was good to renew the PCV system regardless. But it’s just incredible to me that all of this was due to somebody at the dealership being careless when they were working on the car.
I’m also a little bit surprised that given the seepage and what must have been loss of boost, that no check engine lights were ever set off, and that I could still get over 26 mpg.
I do have to wonder if I will see a decent economy improvement given the efficiency increase of at least the turbo. I guess what was really happening was the loss of boost behaved kind of like a stuck open waist gate. And given that his engine makes plenty of power for my needs, And that I don’t really drive it high boost very often, perhaps the turbo just had enough overhead to provide what was needed.
Knocking on wood, that things will stay nice and dry for a while!
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