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1991 W124 300E
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1991 w124 300e m103 445k

I just pulled the fuel distributor and air metering unit off to access the throttle body for the first time. There is oil pooled down in the intake manifold visible when you open the throttle body. What’s going on here!?

2624092
2624093
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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Variable volume intake plenum
pretty sure thats a CIS-E M103 not a HFM M104, so it doesn't have a variable intake manifold

anyways, crankcase fumes are ventilated into the intake via the PVC system, and those fumes are oily, so its actually fairly normal.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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pretty sure thats a CIS-E M103 not a HFM M104, so it doesn't have a variable intake manifold

anyways, crankcase fumes are ventilated into the intake via the PVC system, and those fumes are oily, so its actually fairly normal.
I thought on a M103 the PCV goes straight into the air filter housing which means the filer would also be oily.
Is the outlet past the air filter?

I do not believe it is normal to have oil going into the Air filter housing.
Mine is bone dry (still, hopefully stays that way)
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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7,111 Posts
it is vented inside the air filter, so its sucked into the engine directly. The air sensor plate, and the throttle both can get pretty nasty with combustion blow-by.

this was our 260E with only about 50k miles of 'little old lady'...

 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I see. So if the area is pretty dry like mine the blow-by must be under control as my engine is tired. That is the only good news of the day....

- Cheers!
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,720 Posts
Would it not have made sense to exhaust the blowby prior to the filter so it is filtered and not make a mess at the throttle? I suppose clogging the air filter up would not have been good for the engine though. Perhaps that is the reason.
 

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Premium Member
1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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7,111 Posts
Would it not have made sense to exhaust the blowby prior to the filter so it is filtered and not make a mess at the throttle? I suppose clogging the air filter up would not have been good for the engine though. Perhaps that is the reason.
exactly. its all burnable stuff.

my 260E belonged to the proverbial little old lady in Carmel, California. She lost her license and it sat in her driveway until she died, and my friend inherited it. It had about 50K miles, and stumbled and stalled and noone could fix it, so he gave it to another friend who played with it for a few months then gave it to me. after a year or so, I finally got it sorted out (new CIS injectors and seals). the pics above were fairly iearly in my process of sorting it out. it had a bad air sensor potentiometer, and it had a bad EHA. I renewed the whole ignition system to OEM parts, replacing cheap parts that previous mechanics had slapped on trying to fix it (the blue silicone spark plug wires that looked like a christmas tree at night were really precious).

So, The 2.6L engine had about 50K miles of classic 'little old lady' driving, then a year or two of stumble and stall lets get this thing fixed driving. it was weird, it would run fine for a week, then stall 3 times on the same day. once it was rolling, it was just fine.

since its been sorted out, its had the piss driven out of it, probably 100K of my college son doing 120MPH desert highway runs in Nevada, and trying to see if it can jeep... and I've been driving it now again for a few months. I should pull the air cleaner and inspect the throttle, hah hah. it runs like a new car, I just wish it was a 300 and not a 2.6
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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I should add.... this is the 'rat benz' we are talking about. that LoL in Carmel? she dented every panel. then it sat in her driveway and the paint peeled off. its even got some shallow rust boogers.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,720 Posts
My W201 was driven occasionally (after the first 10 years) and short distances. Last six weeks I have been driving it 20 miles to work everyday to get it to "breathe" before the smog test. Seems to run better and better every day. Hopefully it will pass smog next week, assuming smog centers are staying open .....

PS. Timing chain work is waiting for passing the smog test....
 

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W124
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When a piston rises in the cylinder bore, pressure is created, and the compression rings and the piston's surface area prevent the compressed air from leaking down. This is "compression 101" and we all know this. We also know that when the upper rings and ring lands on the pistons wear, a small portion of the compressed air passes the rings and for a moment pressurizes the crankcase.

Used to be that this pressure was just vented out into the atmosphere and that was usually the reason why older, well worn cars would belch smoke from the front of the car and not the tailpipe. The leaking compression was grabbing oil off the oil ring and it was atomized and partially burned by the heat created during the power stroke. The escaping air also took small droplets of air off the "spray" of oil circulating under the cam covers.

Since PCV, all this oil has been routed back into the intake. Its totally normal for an engine of the M103 era to be collecting oil in the intake because of this. More recent designs have an oil separator in the PCV system that, as its name implies, tries to keep the oil out of the air being routed back into the intake.
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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W124
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Here is a video of a guy cleaning his. Its a rudimentary baffle but surely stops some of the oil from passing into the intake. The current generation of oil separators is more specialized and usually incorporate a PCV valve into them.

 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Always wondered how effective that oil separator is to eliminate the hot oily blow by fumes from the air.
It just has a couple of tiny passages, that's it.
Still not convinced it is that effective but it must be as my return to the air filter box is very dry. I keep looking for some trace of oil there and have never been successful in proving that some of the oil is getting thru.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,720 Posts
Blow-by = Throttle lube :) Agree Dolucasi that the W124 oil separator is rudimentary at best.
I wish Mercedes had put something more substantial in the sheet metal pan with the metal tube on it they call the separator. Though "more substantial" could clog up, and now you have a bigger problem.

I still think venting the valve cover prior to the air filter would have been a good idea. At least that is a serviced item and if there is clogging there, you will notice it as the engine would starve for air. And one would notice that there is excessive blow by when you change the filter.

Anyway, we are not going to re-engineer the M103 here, Mercedes probably knew what they were doing 30 years ago.

- Cheers!
 
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