Negative engine blow-by ?? - Page 2 - PeachParts Mercedes-Benz Forum

ah-kay · #16 07-21-2015, 04:49 PM

There is a big rubber bellow attached to the turbo. The valve cover ventilation tube ( next to oil filler cap ) is plugged into the bellow. If the blow-by is minimal or next to nothing then wouldn't the bellow suck some gas into the turbo to create negative blow-by?

I may remove the valve cover ventilation tube into the bellow and do a test.

97 SL320 · #17 07-21-2015, 07:01 PM

Given these engines have a throttle plate, intake manifold vacuum exists so a pressure regulation valve is needed. ( What i referenced in post 9 was for diesel engines without a throttle plate. )

Have a look at this pic and the thread below.

http://www.benzworld.org/forums/attachments/w124-e-ce-d-td-class/378948d1307128359-crankcase-ventilation-excess-oil-slide4.jpg

Crankcase ventilation - excess oil - Mercedes-Benz Forum

Mxfrank · #18 07-21-2015, 07:48 PM

It's amazing how a trivial question can produce progressively more absurd answers. Let's wrap this up quickly:

It's turbo vacuum, as I was trying to tell you ten posts ago. I tried your experiment on my 190DT. Same thing...there's negative pressure in the crankcase under all conditions. But when I disconnect the breather elbow that feeds into the turbo, just like that, positive pressure. Try it. Be happy.

BillGrissom · #19 07-21-2015, 11:59 PM

Perhaps the scattered answers are because we don't know which of their 5 M-B cars the OP is talking about. Always tell us.

ah-kay · #20 07-22-2015, 12:43 AM

Quote:

Originally Posted by ah-kay

It is a 87 300D OM603. Car runs fine. I have not taken it to the open road yet as it is registered as no-op. What can cause negative pressure inside the valve cover?

Did I specify it is an OM603 turbo in #5?

MxFrank - I misinterpreted your post 'Turbo?' as Turbo engine? and not it could be caused by the Turbo.

None of the other turbo OM603 give this strange behavior hence I asked the question. May be the 87 300D has the best engine of all. It is probably true as it has more power than the rest. Thank you all for the answers. I am happy now.

BenzTurbo · #21 07-22-2015, 04:06 AM

i bet it is the air flow meter causing it. it has a spring loaded metal flap that the engine has to suck to keep open. but still, you must not have much blow-by at all!

Maxbumpo · #22 07-22-2015, 09:08 AM

Glad you figured it out!

Quote:

Originally Posted by ah-kay

MxFrank - I misinterpreted your post 'Turbo?' as Turbo engine? and not it could be caused by the Turbo.

"What we have hear, is FAILURE to communicate!"

Almost every single organizational failure is either caused by or contributed to by a break down in communications; this forum is no exception.

Writing well, so that what you mean to say is understood correctly by the other party, is not easy, and this thread is a great example of that. I understood what MxFrank was saying, and agree with him, but now I see that your understanding of his post and my reply did communicate what we intended.

sloride · #23 07-22-2015, 09:45 AM

Quote:

Originally Posted by Stretch

Indeed - alternatively perhaps air being drawn from the crankcase into the intake as some form of emissions control (gone wrong / malfunctioning)

What route would be taken for crankcase air be directed to intake in a turbo engine? Except a completely clogged air filter drawing air in through the breather tube.

Maxbumpo · #24 07-22-2015, 09:58 AM

Both the air filter and flapper valve are upstream of the breather tube. I guess the flapper valve is part of the emissions control, if that failed closed then the intake would be under vacuum before the turbo-inlet.

Without a picture, I'll do my best to explain. Air is drawn into the filter box, across the air filter, through the flapper valve, and then goes through the intake rubber bellows for the turbo. The breather tube comes from the valve cover down to that rubber bellows, so between the flapper valve and the turbo inlet.

redoubthill · #25 07-22-2015, 04:54 PM

Perhaps the title of the original post would have been better defined as negative crankcase pressure.

Negative engine blow-by would be an anomaly.

ah-kay · #26 07-22-2015, 05:38 PM

Quote:

Originally Posted by redoubthill

Perhaps the title of the original post would have been better defined as negative crankcase pressure.

Negative engine blow-by would be an anomaly.

Every forum I frequent refer the oil filler cap test as the blow-by test. I found the blow-by was non-existent. The cap was sucked down instead. I termed it 'Negative blow-by'. Is it a good term? I am not sure because I am not an auto mechanic. Was it understood by others? Yes. This is NOT a Language Forum.

Mxfrank · #27 07-22-2015, 07:32 PM

A 60x tubo engine ALWAYS has "negative blowby". Actually negative crankcase pressure. This is because the crankcase vent feeds directly to the turbo inlet (via the 'bellows'). The pressure there is negative, even at idle. If you want to test your blowby pressure, disconnect the breather hose. That's the whole story.

ah-kay · #28 07-22-2015, 09:49 PM

Quote:

Originally Posted by Mxfrank

A 60x tubo engine ALWAYS has "negative blowby". Actually negative crankcase pressure.

Really? Are you saying the tea-pot test every one does with a OM60x turbo engine is meaningless?

Stretch · #29 07-23-2015, 02:38 AM

Quote:

Originally Posted by sloride

What route would be taken for crankcase air be directed to intake in a turbo engine? Except a completely clogged air filter drawing air in through the breather tube.

I'm not quite sure what you mean - if the air filter was completely clogged the engine would be starved of air (and much like the method used to stop a run away diesel) it would stall...

...a breather tube isn't always the only bit of kit used to distribute and control crank case gasses. Different systems are adopted to deal with =>

Quote:

Originally Posted by redoubthill

... negative crankcase pressure.

...

(Good terminology)

Perhaps I should have made it clearer earlier on but I was trying to not give a long winded explanation here =>

Quote:

Originally Posted by Stretch

Indeed - alternatively perhaps air being drawn from the crankcase into the intake as some form of emissions control (gone wrong / malfunctioning)

To the best of my knowledge nobody has managed to make a perfectly sealed piston in a cylinder and incorporate this into a combustion engine - gasses will always make their way into a crank case (mostly via the piston)

You can say "blow-by" always exists

Manufacturers deal with these gases in different ways (whether a turbo is fitted or not) but in general the crank case gases are more often than not stubbornly sent back into the cylinders via the intake manifold.

How these gases are sent back into the cylinders is type / system specific. Even within a type such as the subject of this thread (the OM603) there are at least two different systems - as often seems to be the case with Mercedes and is often referred to here as => Federal and Californian.

Some form of crank case pressure management system exists.

This has been designed among other reasons to

1) Stop the pressure in the crank case from increasing to a level that seals start to pop out of the engine

2) Stop nasty smells and evil gas juices (!)

3) And in the case of a turbo charged / forced induction system - stop a vacuum from being formed within the crank case which would tend to increase or encourage yet more blow-by (and perhaps cause other trouble)

Quote:

Originally Posted by ah-kay

Really? Are you saying the tea-pot test every one does with a OM60x turbo engine is meaningless?

I don't think the "tea-pot test" is meaningless - it just means / indicates something that you perhaps were not expecting. In your case an apparent vacuum in your crank case indicates trouble with what ever gubbins have been fitted to your engine to control the crankcase pressure.

"Summits up" because a vacuum is undesirable just like excessive pressure.