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Old 08-09-2004, 11:20 PM   #1 (permalink)
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Can any M5 owner tell me if S38 engine should have vacuum in the valve cover area? In other words does RPM change on your engine when you remove oil cap, when engine is running? I have to ask this question since no tehnical information about this engine is available anywhere (only to BMW dealers I asume).Thank's in advance.
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Old 08-09-2004, 11:25 PM   #2 (permalink)
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of course the RPM is going to change when you open the oil filler cap while the engine is running! You just created a HUGE vacuum leak.
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Old 08-09-2004, 11:44 PM   #3 (permalink)
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So you are sure about vaccum being present in the valve cover area on the S38 engine(multiple throttle bodys)?
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Old 08-10-2004, 08:50 PM   #4 (permalink)
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Yes I am sure about the Vacuum.
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Old 08-10-2004, 10:27 PM   #5 (permalink)
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So what creates vacuum in the valve cover area on the S38 engine? I don't see any ralation between throttle bodys & valve cover or crankcase. The only vacuum lines that run of the throttle bodys are to control air pump,resonance change over flap, purge valve(gas fumes) & to IAC valve/motor. So please explain to me what creates vacuum inside block & valvetrain area? Thank's in advance
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Old 08-12-2004, 09:10 PM   #6 (permalink)
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The PCV system is what creates vacuum in the crankcase....even though there may not be any vacuum lines going to the Valve Cover doesn't mean it is uneffected by the Vacuum created to releave Crankcase pressures so you don't blow out your seals. The PCV works along the lines of it created a negative pressure differential which pulls crankcase vapors back into the intake system to be consumed in combustion...I hope this answers your question.
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Old 08-12-2004, 10:34 PM   #7 (permalink)
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Sorry,that does not answer my question. This engine does not have a PCV valve. It has the oil separator and it is there to separate oil that gets blown by from the valve cover. Oil separator is part of the plenum and it is also connected to the engine oil dipstick,to drain oil back in to crankcase. At the same time the air gets "sucked" back in to throttle bodys thru plenum and there is no vacuum in the plenum,just air flow. As far as I understand this engine can not have vacuum in valve cover area because it is venting in to plenum thru valve cover & oil dipstick tube,also there will be no pressure inside crankcase or valve cover. The reason why I am asking about vacuum is because there is no information about this engine anywhere(including Mitchell,AllData,& few tec-lines that I have access to). Every BMW mechanic that I asked about vacuum on this engine did not have answer for me. I want to ask you if you are familiar with S38 engines? I need a 100% answer,not a guess. Thank you in advance for your time.Take care.

P.S. I am pretty sure at this point that there is no vacumm in a crankcase or valve cover area.
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Old 08-13-2004, 09:22 PM   #8 (permalink)
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it doesn't matter if it's an S38 or an M54 engine principals are the same. Crankcase is going to build up pressure, so you need a way to evacuate that pressure build up or bye bye seals...point blank. Positive Crankcase Ventalation is ONE system (that's been around since FOREVER) to relieve this build up....unless your S38 has valve cover breathers (which would make your S38 one of a kind) Valve cover breathers only pose atmospheric pressure on the system, and that is the only system that doesn't create a pressure differential (aka: vacuum)

" As far as I understand this engine can not have vacuum in valve cover area because it is venting in to plenum thru valve cover & oil dipstick tube,also there will be no pressure inside crankcase or valve cover"

so explain to me how does this venting occur from the valve cover and oil dipstick tube to the plenum without vacuum/vacuum lines??? There will be pressure in the crankcase no matter what engine it is (chevy, ford, dodge, or bmw) due to the downward forces exerted on the crank by the piston assembly...just as vacuum is created on one side of the piston, pressure is created on the other side....
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Old 08-14-2004, 06:51 PM   #9 (permalink)
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Seems to me that you are trying to teach me principles of the engine operation that I learned a long time ago. About that quotation, maybe I did not express myself properly. What I meant to say is that the crankcase & valve cover are connected to the plenum & because of that no pressure will exist in the crankcase,because of the venting. Let me ask you how do you create a vacuum in the plenum that is completly open to the atmosphere thru MAF. Also throttle body plate(all six of them) are past the plenum,between the plenum & the head. Also the crank case is being vented into the plenum. So how do we get a vacuum in the valve cover area & how does removal of the oil cap create a HUGE vacuum leak?Maybe this will help.If we block these vents will we get pressure in the crank case?There is no vacuum in the plenum.How do we get a huge vacuum leak when the oil cap is removed? .Can you explain this to me? By the way are you a mechanic or you are spending lots of time acting like one?

P.S. I just wanted an answer,but you started being smart.(THIS ENGINE DOES NOT HAVE A PCV VALVE!)
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Old 08-15-2004, 10:53 PM   #10 (permalink)
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take the oil cap off with engine running and see what happens, I mean it's not like that would be unmetered air entering the engine or anything...and no I'm not a mechanic nor do I want to pretend to be that low on the food chain...once again I must ask if the plenum does not have vacuum how does the air fuel mixture get drawn into the cylinder?? it doesn't just wander in there by mistake...or maybe I'm wrong and the S38 *(of yours)* defies all laws of engine pricipals. If you do not have a breather on the oil fill cap, then you have some sort of Positive Crankcase Ventalation (not saying you MUST have a PCV Valve persay, but a system that releases the Pressures in the crankcase)...you may have a funny way of wording things..but you create vacuum in the plenum when you start the engine and that piston starts to make it's travel down ward, but you should have already known that. Yes if you block all sorts of venting from the crankcase, you can say goodbye to your seals...because the engine will find a way to evacuate that pressure, and it will go through your weakest links aka. oil seals....but you probably already knew that too...
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Old 08-17-2004, 07:03 PM   #11 (permalink)
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I am not here to prove anything. I asked about the vacuum because I was not getting any @ the oil cap. After taking of the plenum & making sense of this engines design I discovered that there will be no engine vacuum under the oil cap(I did not know this a few days ago & like I said nobody had an answer). What bothers me is that you confidently said that the vacuum will be present in that area & that I will create a HUGE vacuum leak if I remove the oil cap. You should not answer questions about things that you are not 100% sure about,or you should say that you are not sure. Also the vacuum on this engine & any other engine will be present when the engine is running only after throttle body(between throttle body & head,not throttle body & air filter). Air only fllows in that area towards the intake/throttle body. Plenum will have vacum if it is located between the throttle body & head(any regular BMW engine,or any other make). One thing you are right about,one or more seals will get blown if the crankcase is not being vented(bad PCV can be enough for that to happen). So do you agree that there will be no vacumm in the valve cover area due to "pressure" caused by pistons travel up/down?There will be no pressure in the crankcase due to breather tubes. Because the crank is getting vented in the plenum/oil separator, which is part of the plenum & it is hollow inside like a pop can (it does not work like a PCV valve)...but you probably knew that..You may say that I have a funny way of wording things but if you were not acting smart & being sarcastic you would not answer my question the way you did. That made me change the way I am talking to you. I did not start this conversation in this tone,You did! By the way, if I did word my post in a funny way,I apologize because english is my second language. Take care.

P.S. I would like to know if you agree with me on this subject (S38 vacuum)
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Old 08-17-2004, 09:29 PM   #12 (permalink)
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Possibly S38, it is so old I would never see it in the dealership...but I do not agree about the lack of vacuum in the plenum, because I have experienced 1st hand that vacuum is created in the plenum...as the pistion travels downward it creates a large open "hole" which creates a pressure differential in which air rushes to fill as soon as the valve opens...you can actually feel, hear, and sense a change when you pull the oil fill cap off most engines. This is why I strongly protest....Pull the oil fill cap off a, for example, 2002 X5 M54B30 the RPM changes, and if you put your hand over the hole, you can feel a "suck" of course you also make a big oily mess in the process...This is something I have actually seen first hand and felt with my own hands...This I know for a fact. I do not tend to "guess" here, I'm sure you can even admit there are far to many "stupid people" in the world that would take guesses far to litterally and screw things up...like I said, the S38 is way too old for me to see on the dealership level, and the assumption was made that it would be just like any other engine on the market on any line.
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Old 08-18-2004, 06:36 PM   #13 (permalink)
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Yes, you will feel vacuum under oil cap on X5 (X5 has "PCV system"). Because on X5 plenum is after throttle body,so there is vacuum in the plenum,as well as 99% BMW engines. But I was not talking about most of BMW engines. I said that long time ago. At your last post you are finaly telling me that you were guessing after 12 posts (between two of us). This is why I asked if you were sure about vacuum under oil cap on S38 engine. No hard feelings,thanks for your time & take care.
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