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1998 SLK 230
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Discussion Starter #1
I have done this to my car a long while back, no oil is EVER present in the intake system. I vent it to atmosphere and hide the breather near the transmission tunnel so its out of sight and the fumes are away from the air intakes to the cabin of the car. also stops the excessive oil vapor being sucked into the intake playing with the air fuel ratios.

reason why it fails is there is a rubber hose from the two circled points. this hose is near the exhaust and over the years becomes brittle and fails. once this hose goes the system fails to work properly, and you get problems like contaminated MAF's and dirty intercoolers. for a stock car i would replace that rubber hose its 3mm or 5mm vacuum hose from memory.

if modifying it, close it shut as this WILL ACT AS A BOOST LEAK robbing a psi or two. Please do NOT shut this if keeping the factory system and venting back into the airbox.

if this hose is split open, which given the age chances it has, will also act as a boost leak.

i have a slight kink in my outlet hose but it doesnt cause any dramas. never have to worry about a dirty MAF.
 

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2008 ML 350 4MATIC W164 Gas VIN: Last 7 Digit: A308649
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114 Posts
Subbb - Excuse me but I did not understand how exactly you solve this problem and how you vented hose. Did you mean hose circled in your picture you close it from both side ? That solved problem ? Or You vented some other hose ?
 

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2002 SLK 230
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Everybody should do this! There is absolutely no point in letting your entire intake system from the supercharger to the engine serve as a catch can, rob performance as oil builds up, and foul your MAF sensor.

I have a question about the low pressure/load PCV under the intake manifold. Mine is clogged and I ordered the hose and valve to replace it, but I have been wondering if there is any negative effect to essentially doing the same thing for it. (aside from venting a little blowby fumes into the atsmophere) . I would think you can just cap off the nozzles on the block and run a tube from lower breather to a catch can or air/ground as well. It will basically only work when the throttle body is closed and there is a vacuum in the intake manifold. I am sure it contributes to better fuel economy just like the EGR by putting non-combustable gas into the chamber and slightly leaning the mixture (lower pcv puts air in after the TB/MAF), but it cannot be much air through those small nozzle openings. I contemplated deleting the EGR also, but without tuning to compensate, the ECU expects that gas to be in the mixture, and I believe it probably has a noticeable impact on economy when you are just cruising on the highway, which I do a lot in my car.

Let me know if anyone has done this, has any input, or knows of a reason not to do it and why. I thinking about trying it out, and it will be much easier to do than remove the manifold and all that goes with it in order to be able to clean the nozzles!
 

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Everybody should do this! There is absolutely no point in letting your entire intake system from the supercharger to the engine serve as a catch can, rob performance as oil builds up, and foul your MAF sensor.

I have a question about the low pressure/load PCV under the intake manifold. Mine is clogged and I ordered the hose and valve to replace it, but I have been wondering if there is any negative effect to essentially doing the same thing for it. (aside from venting a little blowby fumes into the atsmophere) . I would think you can just cap off the nozzles on the block and run a tube from lower breather to a catch can or air/ground as well. It will basically only work when the throttle body is closed and there is a vacuum in the intake manifold. I am sure it contributes to better fuel economy just like the EGR by putting non-combustable gas into the chamber and slightly leaning the mixture (lower pcv puts air in after the TB/MAF), but it cannot be much air through those small nozzle openings. I contemplated deleting the EGR also, but without tuning to compensate, the ECU expects that gas to be in the mixture, and I believe it probably has a noticeable impact on economy when you are just cruising on the highway, which I do a lot in my car.

Let me know if anyone has done this, has any input, or knows of a reason not to do it and why. I thinking about trying it out, and it will be much easier to do than remove the manifold and all that goes with it in order to be able to clean the nozzles!
Did you do this mod without cleaning the low load PCV under the intake manifold?

I have done this mod but I am sure the low load PCV is blocked on my car (lots of KM) and wondering if there is any issue but leaving it so. I can very rarely see some vapor coming out of there but no oil whatsoever.
 

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1998 SLK 230
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Discussion Starter #5
i havent touched the low side under the intake manifold and it hasnt given any problems in years...
 

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W202 230K Sport manual & a few non Merc's
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i havent touched the low side under the intake manifold and it hasnt given any problems in years...
Obviously a well serviced with regular oil changes and giving it plenty of WOT might have something to do it it? :smile

Out of interest Subby, what mileage is on your engine?
 

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1998 SLK 230
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Discussion Starter #7
its approx 220,000 kms or 136,000 miles
 

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1999 C230 Kompressor. 1994 E220 before that (totalled)
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venting to atmosphere is 'good'?
I do have a fouled MAF currently and trying to see what I can do as far as getting the job done for not too much money.
I was thinking to keep the stock breathing system, but hopefully use custom hoses. Any reason one can think of that would result in problems with my idea? stealership wants a lot of money for the hoses, let alone the MAF.
 

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2008 ML 350 4MATIC W164 Gas VIN: Last 7 Digit: A308649
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venting to atmosphere is 'good'?
I do have a fouled MAF currently and trying to see what I can do as far as getting the job done for not too much money.
I was thinking to keep the stock breathing system, but hopefully use custom hoses. Any reason one can think of that would result in problems with my idea? stealership wants a lot of money for the hoses, let alone the MAF.
Buying anything from Stealership is not a good idea. for MAF, you shojuld able to get new one in rage of $100-120 BOSCH. Do not buy any after market, it will NOT work.

For hoses, it does not matter what hoses you use as far as size match and it is durable.
 

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2003 SLK230 USA model, Auto Transmission, Stock, Firemist Red
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I do have a fouled MAF currently and trying to see what I can do as far as getting the job done for not too much money.
I was thinking to keep the stock breathing system, but hopefully use custom hoses.
Use the right maf cleaner. I used CRC Mass Air Flow Sensor Cleaner. If that does not help, check eBay for best price.
You can buy metric hose by the foot at auto parts stores.
 

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1999 SLK230 2009 E350
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My experience has been the proper maintenance of the low pressure PCV and associated lines is the key to preventing massive amounts of oil to enter the air intake. If the valve is stuck open, the positive pressure created when the super charger kicks in will blow air through the engine oil and it will exit into the oil separator and overload it. Think of kids blowing into a straw when drinking milk but in this case it is the engine oil that is being made into a foam. The check valve is designed to close and prevent this. Obviously when it is stuck it won't. Now disconnecting at the separator end will prevent the oil from entering the air intake but all that air and oil is still blowing back through the engine and venting off. At the very least the oil is being lost. I am not sure what negative affect all that air going though the engine will be created. I had about 150K miles on my car when I replaced mine. I am at 278K now and thinking I need to replace the valve again just to stay ahead of the problem.
 

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Thanks Subby. I found carryover oil in the airbox and when I checked there was a split in the 3mm vacuum hose that was not readily visible. Replaced the hose.

I've modified the oil vent system as per your advice but left the 3mm vacuum hose connection intact.

There's enough MAF oil contamination horror stories on this forum to make this modification worthwhile, in jurisdictions where it's allowed.
 

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w202
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I've modified the oil vent system as per your advice but left the 3mm vacuum hose connection intact.
Do you have a boost leak now? I'm pretty sure if you vent to the air, you are supposed to remove the 3mm hose, cap off the port on the oil separator, and cap off the port on the supercharger.

Read below, it's right in the OP

for a stock car i would replace that rubber hose its 3mm or 5mm vacuum hose from memory.

if modifying it, close it shut as this WILL ACT AS A BOOST LEAK robbing a psi or two. Please do NOT shut this if keeping the factory system and venting back into the airbox
 

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1998 SLK 230
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Discussion Starter #14
yes 100% cap that 3mm hose off the supercharger as you will have a boost leak.
 

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Wouldn't a true catch can be better than this? The way shown here still lets the oil drain back into the oil pan, or can(should) we just delete that hose?
 

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1998 SLK 230
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Discussion Starter #16
yeah that could work, but the tricky bit is finding a location to put it in a very tight engine bay. it is also illegal in most areas for emissions reasons for road legal cars to vent crank case emissions to atmosphere so need to take into account being discreet.

keeping the factory oil separator will still drain any oil back into the dipstick tube back to the sump but the key is not connecting the pipe that goes to the airbox. this is the pipe that causes drama which coats the whole intake system with too much oil vapor.

i can see why they did this, before the supercharger to allow suction to suck more oil vapor to burn it part of combustion, but then it causes the intercooler to loose efficiency (dirty) and MAF to be contaminated over time...
 

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^Gotcha! Emissions aside, what about eliminating the spiral oil separator all together and just run a dump hose with filter right off the nipple on the valve cover? Capping everything else off of course. Only downside I can see is that you lose some oil? Can't be that much oil loss to make a difference, or do these engine blow a lot of oil through the valve cover? I haven't had my VC off yet to see if there's any kind of oil splash guard inside.

On my audi 1.8t I deleted the whole PCV system and dumped straight to the ground with hose and filter and never experienced any noticeable oil loss when checking the oil. Ran good for years that way.
 
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