M54 Oil Consumption - two possible fixes, which is better?

UK forum for general and technical discussion about the Z3 roadster
Post Reply
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

Looking at the issue of M54 oil burning with regard to my 2002 2.2 Z3 I have found two different approaches short of stripping the engine and changing the oil control rings. In the first http://www.youtube.com/watch?v=Fo2rLSzNzt0 the guy installs a new piece of tubing to generate extra vacuum in the crankcase. This, he says, completely stops the oil burning.

In the other approach, http://www.e46zone.com/forum/topic/4142 ... 54-engine/ the guy says that you need to replace your CCV valve and plumbing because it gets all crudded up.

Has anyone any experience of either or both jobs and if so which one works?

Mike
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

I replaced the CCV and tubing on mine. The old parts were pretty clean.
It made absolutely no difference.

I'm thinking about trying the vacuum connection but I don't understand why it would work. Looks easy enough to try though.....
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

Yes, I was wondering if I would end up doing a somewhat tricky and reasonably expensive job to find it made no difference. However, the author's own components seemed pretty claggy - I wonder what mine are like? As for the extra vacuum line, I would have thought there would be a possibility of upsetting the car's running, knowing how sensitive the computerised systems are to changes. But as you say, it wouldn't be hard to fit it, and then remove it if it is no good.

I wonder why BMW, in their wisdom, lumbered this engine with an inferior design of oil control rings?
Joycey
Joined: Mon 11 Jul, 2011 22:15
Posts: 290

  M roadster S52
Location: Basingstoke

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Joycey »

I went through all this last year with the wifes 2.2 The oil rings on the piston are either gummed up or passing.

The extra vacuum line did work for me because you're introducing extra pull onto the rings but you could feel the draw on the engine. So i ended up removing this.

The only solution I've found was thicker oil. I now run 10w60 and all my issues have gone. Even dyno'ed the car at 168bhp. The only other way I've heard alot of people doing is using an oil catch can.

Lee
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

Lee, I agree that a thicker oil could be a solution although I haven't heard of anyone using a 10W-60 before. Are you using a full synthetic, part-synthetic, or mineral oil? On zroadster.org where I posted the same question, several replies have said that changing the CCV set-up did help, and one said that the fuel treatment BG44K made a big difference. No-one on there liked the idea of the extra vacuum line.

Thanks to all for the advice so far.
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Joycey wrote: Wed 13 Jun, 2018 20:38 I now run 10w60 and all my issues have gone.
10x60 ? That's actually outside the spec of acceptable oil as specified in the handbook which says 0W-X or 5W-X, where X any desired upper viscosity limit

Won't it cause increased engine wear?

Note I am no oil expert. Just asking :-)
nang
Joined: Sat 25 Jun, 2016 03:27
Posts: 51

  Z3 roadster 2.8

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by nang »

What sort of milage has she done ? Could be just worn out :shock:
tony.
Joycey
Joined: Mon 11 Jul, 2011 22:15
Posts: 290

  M roadster S52
Location: Basingstoke

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Joycey »

My understanding behind all of this is the design change done by BMW regarding the scraper ring, sit an M52 and M54 scraper ring next to each other and you can see the problem.

I also experimented with some oil treatments and got good results from Seafoam, think my video is on zroadster.org somewhere.
Tufarlian wrote: Fri 15 Jun, 2018 16:51
Joycey wrote: Wed 13 Jun, 2018 20:38 I now run 10w60 and all my issues have gone.
10x60 ? That's actually outside the spec of acceptable oil as specified in the handbook which says 0W-X or 5W-X, where X any desired upper viscosity limit

Won't it cause increased engine wear?

Note I am no oil expert. Just asking :-)


I'm sure it is out of spec according to the handbook but the handbook dont give you any guidance on a 150,000 mile engine. Nothing abnormal to report so far, around 8000 miles since the last service.

These engines are moisture traps if you do short journeys I found the problem nearly went away using it for my long commutes.
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Joycey wrote: Tue 19 Jun, 2018 16:45 ......the handbook dont give you any guidance on a 150,000 mile engine. Nothing abnormal to report so far, around 8000 miles since the last service.
Good point. Not got to 150k yet but I think I will try it at the next oil change
Joycey wrote: Tue 19 Jun, 2018 16:45 These engines are moisture traps if you do short journeys I found the problem nearly went away using it for my long commutes.
Mine has always used a lot less oil on long runs than it does on short ones.
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

The options are change the oil rings on the pistons and fit the rings from the M52's. They are a better design.
Or... delete the CCV completely and fit a decent oil catch can like Mishimoto. The cheap eBay £20 ones are crap and don't come with all the bits to do the job.
The vacuum hose idea needs to drain the oil to somewhere, and other than the CCV system where it's supposed to be drained from and back to the oil pan / sump via a secondary tube built into the dipstick tube. You could remove your dipstick tube and check this almost useless idea isn't clogged up, and if so, get it seriously well cleaned to allow oi to drain through again. Removing the dipstick tube is very easy. 1 x M10 bolt at the top end, 1 x M13 bolt at the bottom. Disconnect the oil drain pie at the Y junction - this pipe comes from the bottom end of the CCV. Un-clip some other tube which has a plastic carrier attached to the dipstick and then simply yank the dipstick tube straight up and out.
There's a rubber O ring at the bottom of the tube where it seals into the sump. Make sure it's on the dipstick just below the little flange at the bottom. If it's not, fish it out the entry hole into the sump. Check this O ring for it's elasticity and fit. Replace if you think it needs renewal. If you turn the dipstick upside down, look on the outer edge of the main pipe which the actual dipstick goes down. you will see a secondary pipe into which the hose from the bottom of the CCV drains into via the Y joint further up the dipstick tube. A good soak in a strong de-greaser and hot water should clear the system. Alternately, use a power washer to blast through it until it's good.
If you're interested in a concise explanation of the CCV vs Catch can options - go to this link.

http://www.onallcylinders.com/2014/04/1 ... separator/

The bottom line is - the M54 engine has crappy oil rings, and unless you change them, get used to oil consumption.
"Normal is overrated"
Image

Z3 Upgrades and Additions
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

Thank you Southernboy for your comments. I am looking into the oil burning issue at the moment and as I haven't had my car long I am not sure yet what the oil consumption is like with 78,000 miles on the clock. Your description of cleaning out the dipstick tube is a good idea and I shall have a go at that. If my M54 is an oil burner I think I will consider the Mishimoto catch tank for now which I assume replaces the CCV valve.

I realise that changing the piston rings is the proper solution, but I really don't want to tear down the engine at this time. It's funny but never having owned a BMW before I assumed it was a better quality car than the cheaper brands, but I have quickly come to realise that it has just the same sorts of issues as all the mass produced European cars. Disappointing really.
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

All M54 engines have the same oil consumption issues. The CCV isn't particularly a weak link, but has to cope with the volumes of oil due to the oil ring problem of those engines.
If you look at how the CCV works, the fitting of a catch can does not mean you have to replace the CCV. A catch can has an inlet and exhaust side. The perfect solution is to fit the inlet side to the valve cover and the exhaust side to the CCV where the OEM hose from valve cover to CCV would otherwise fit. This means you are passing the "dirty" oily air through the catch can before it gets to the CCV. The CCV then will filter / remove any further oil from the now 90% clean air and then pass the air back into the intake manifold as usual. Any oil it does collect will be passed down via the dipstick secondary tube and back into the sump.
A catch can needs to be drained regularly. Obviously it depends on the size of the catch can, how much mileage you do, and the condition of the engine.
I have googled and read, watched you tube videos etc etc on the BMW CCV issue. 99% propose a delete of the CCV. Personally I don't like that idea since it provides a "back up" and acts as a 2nd filter, therefor providing exceptionally clean air into the intake and promoting a cleaner engine and longer oil life. Conversely, if the CCV valve fails, the catch can is already providing excellent filtration anyhow.
The major issue is the prevention of gaseous oil re-entering the intake manifold system. The CCV does a fairly good job of that with the exception of a poorly ringed piston scenario as in the M54 motor where the excessive volume results in a filthy oily cruddy intake manifold, and that same filthy air being passed into the combustion chambers of each piston to be re-burnt and create even worse gunk.
So, bottom line is, nothing wrong with the OEM CCV, it's basically being overwhelmed by a crap piston ring - all 6 of them. The solution is to live with those rings, but at best provide good filtered oil free air to pass back into the intake by fitting a catch can between the valve cover outlet to CCV and the inlet to CCV of the same OEM hose.
To do this is wonderfully simple. Once you have decided where best to fit the catch can so that it is optimally located to the valve cover outlet and CCV inlet points. Once you have done that, you van completely remove the OEM pipe but retain the connectors at either end. All you need do now is fit your new hose from Valve cover with transferred OEM connector to inlet side of catch can. and from outlet side of catch can with new hose to CCV using the retained OEM connector to fit correctly to the CCV again. Simple, and effective. You will need to locate the catch can where you can access it to periodically drain off the collected oil.
In that regard, I have looked at the Mishimoto and the Moroso and concluded the Moroso is better in one important aspect. It has a 3rd pipe at the bottom of the can from which oil can be drained without having to unscrew the bottom half of the catch can as in the case of the Mishimoto.
Also, this 3rd pipe offers the possibility of simply having a tube fitted and integrated using a "Y" connector to the CCV drain pipe which connects to the dipstick. That would provide a practically 100|% hassle free Catch can / CCV system.
Worth considering since the oil from the catch can will be transferred back into the sump, and therefor mostly eliminating "oil consumption" 8-)
"Normal is overrated"
Image

Z3 Upgrades and Additions
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

That is a brilliant and useful answer Southernboy and I have copied it onto a Word document for future reference. I like the idea of draining the catch can back into the sump - it would save much of the topping up that is currently needed.

Isn't it good that folk who live in entirely different parts of the world can converse so easily? My wife and I are taking our Z3 2.2 litre to Ireland soon, and then I shall be going to Silverstone Circuit for the national classic car meeting (350 miles from my home) so hopefully I will be able to assess the oil usage on longer trips.

Mike
By the way, thinking of your by-line "Normal is overrated", my career was in hospital lab medicine and doctors used to ask us for the "Normal Range" for various parameters we measured. We used to ask them to define normal.
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

Happy to be able to pass on some decent advice. I have just recently ordered the Moroso C/Can - large size.
Went out this morning to look where I can best fit it and decided to sacrifice the OEM windscreen washer reservoir. I'll have to find a smaller reservoir to replace it with so I can have space for both items.
Enjoy your excursion to Ireland - I'll bet on you having a magic trip.
I'll post the results of the Moroso fitting with any useful info on how best to connect hoses using the OEM connectors etc etc. It'll help you if / when you get to doing the modification.
"Normal is overrated"
Image

Z3 Upgrades and Additions
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

Great. I'll look out for your further posts.

Mike
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Southernboy wrote: Sat 23 Jun, 2018 10:35 I have just recently ordered the Moroso C/Can - large size.
The Moroso obviously looks to be a really good quality product but it's just a touch expensive. About US$250 including postage on eBay.
https://www.ebay.co.uk/itm/Moroso-85472 ... 1438.l2649

There are lots of oil catch tanks that are much cheaper.
For instance https://www.ebay.co.uk/itm/Universal-Ra ... Sw~K9bI4-q

I know you get what you pay for but that's an enormous difference. Why is the Moroso so expensive?
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

I didn't get mine off eBay. I ordered via sales@frsport.com
$158.00 excl postage.
The Moroso has inner baffles as does the Mishimoto. This means it isn't just a collection canister. The oil is collected in a gaseous condition and it passes below the baffles into the collection area. The baffles which prevent the gas escaping directly thus cooling it which means it condenses into a liquid. On the output side is a further micro-filter which essentially stops any misted oil from escaping back into the intake.
The way the eBay "cheapies" work is so basic that it's hard to imagine much benefit.
The inlet side has a longer tube down into the lower 1/2 of the catch can, where-as the output side has a much shorter tube extending into the catch can.
The idea being that the oil gases will mostly condense and stay at the bottom of the can. They have no baffles or filters fitted. In fact most people buying these "cheaper" versions, use wire mesh, scouring pads etc stuffed into the bottom of the can to create a better form of catching the misted oil and keeping it in the can.
As per my post above, I want to retain the OEM CCV and place the Moroso between the outlet side of the OEM CCV coming from the valve cover and the inlet side of the OEM CCV - which is the other end of the same OEM CCV pipe. That way I have a dual filtration system, the CCV isn't overloaded with 100% of the hot gases as in the OEM set up, and quite likely, the cleaned air being fed back into the intake will be somewhat cooler and undoubtedly cleaner than it would be having only passed through the OEM CCV system. Having clean air ingested into the combustion chambers, will provide better ignition and hence better performance.
On a final note - the only necessity of the CCV on any car is because of emissions. All cars have always had positive crankcase pressure - just that in the past, it was vented directly into the atmosphere. Some while back, this was made illegal and car manufacturers were obliged to "re-cycle" this dirty oily air back into the combustion process to be burnt and expelled out the exhaust system where the cats could clean up before it finally entered the atmosphere.
The cost of employing the CCV system is a loss of performance and hence power due to the air mixture entering the combustion chamber is loaded with incombustible carbons from the previous visits. The oil in the sump into which the CCV deposits most of this dirty oil, is also expected to lubricate the entire engine and all the moving parts like valves, Vanos actuators, crank shaft and cams etc etc, but it is being constantly infused with burnt matter which is why it turns black eventually.
During the normal cycle of combustion air is sucked in and passes through the MAF and then through the throttle body and into the intake manifold. Consider your local weather report telling you that the ambient air humidity is 30% ( which isn't very humid - Hong Kong is around 80 - 90+% air humidity at times) Now as air is sucked in you're also sucking in water vapour which mixes into the burnt mixture. Some of that water vapour mixes into the oil / burnt fuel gases and is expelled via the valve cover and into the CCV system. So you now have a carbon / water/oil and un-burnt fuel mixture being recycled as "dirty oil" back to the sump. The air, after being somewhat cleaned by the CCV, is vented directly back into the intake manifold just behind the injector side and very close to the inlet ports of the cylinder head.
Hope the above gives you some pause as to how much damage your engine has endured over the past 20 some years, and why it is important to try to alleviate that sooner rather than later. Also, it should make your maintenance program more conscientious with regard to oil change intervals, engine flushes to try to keep the sump clean more than anything else. An inspection of the outer drain pipe on the dipstick to ensure what oil is collected by the CCV can drain to the sump and isn't being forced to be fed into the intake. Ask yourself. have you ever removed your dipstick to check that oil drain ? I would guess you, or most drivers have never done it. :wink:
"Normal is overrated"
Image

Z3 Upgrades and Additions
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Well, I did ask :-) and thanks for such a comprehensive answer.

There had to be a difference between them with such a price difference and your explanation makes it very clear.

I have already replaced the entire CCV setup with new OEM parts and will be watching out for your install description for the Moroso.
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

May I ask if you pulled the dipstick out when you did the CCV replacement?
The fact that the CCV has a separate drain channel on the dipstick tube isn't common knowledge, and I would imagine it is not a check item when doing the CCV replacement.
"Normal is overrated"
Image

Z3 Upgrades and Additions
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

No, I didn't actually remove the dipstick tube but the pipe that runs down to it is new.

You're about to tell me it could be still be blocked down there, aren't you? :-)
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

I'm afraid so. The dipstick tube which you shove the dipstick down is an "inner" tube. At the bottom where the CCV rubber drain tube connects to the dipstick, the dipstick tube has a "second skin" around the long "inner tube" but only for the section from that CCV "Y" joint. The gap between the inner and outer tube is small - a couple of mm only. So, it's easy to get blocked up since it's so tight.
Obviously if oil can't get through there, your entire CCV system is useless. :wink:
"Normal is overrated"
Image

Z3 Upgrades and Additions
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Oh boy.

I feel another mucky afternoon is ahead of me......
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

Sorry.... It's very easy to remove though. Pull the CCV hose off, undo the M13 bolt holding the bracket to the engine block near the bottom, remove the M10 bolt at the top end and unclip the cable / hose whatever off the dipstick body about 1/2 way down. The pull straight up and out. Mind the rubber O ring which has a housing in the oil pan. It shouldn't drop in. Just as an aside, check if there is any oil around the sump where the dipstick goes in. If there is, replace that rubber O ring with a new one. :D
"Normal is overrated"
Image

Z3 Upgrades and Additions
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

You're right. It was easy to remove, apart from the bracket being bigger than it looks and getting snagged on everything in sight . :-)

A fair bit harder to refit because of the bracket and all the wires and pipes down there. Got to be very careful not to snag or trap anything.

FWIW it was clear. It wasn't leaking but it got a new O ring anyway.

Thanks for the advice though.
Bumpa
Joined: Fri 23 Jun, 2017 20:31
Posts: 70

  Z3 roadster 2.2i

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Bumpa »

It's a lovely afternoon and I had some time so I thought I would check my dipstick tube. I managed to get the drain pipe off the Y-connector and that looks all clear inside. BUT (there's always a but) I just could not undo the 13mm bolt for the bracket at the bottom of the tube. I have a fair selection of tools including a couple of different socket sets, but with the limited access I just can't get enough leverage to loosen it. It must be extremely tight because I was really straining at it. Bugger.

Incidentally, my dipstick tube doesn't have a top fixing as you describe, just the one immovable bolt at the bottom.

I haven't had much luck finding a supplier of the Moroso catch can here in the UK. I could order it from the USA but the import taxes can be pretty high, and its an expensive item to start with.

Mike
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

Good news and some not so good news.... The M13 shouldn't be that difficult unless it's rusted onto the bracket. Perhaps give it the WD40 treatment and leave it until you get another chance Mike. :wink:
Try looking for the Moroso in Europe perhaps ??
"Normal is overrated"
Image

Z3 Upgrades and Additions
User avatar
Tufarlian
Joined: Sat 14 Mar, 2009 20:21
Posts: 307

  Z3 roadster 3.0i
Location: Cheshire
Contact:

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Tufarlian »

Bumpa wrote: Sun 24 Jun, 2018 15:33 Incidentally, my dipstick tube doesn't have a top fixing as you describe, just the one immovable bolt at the bottom.
No top fixing on mine either and the bolt was tight. Managed to get a 1/4 drive ratchet and extension on it but it was tight.
Flight
Joined: Mon 16 Sep, 2013 20:43
Posts: 97

  blank

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Flight »

Have followed this topic with interest. What amounts of oil consumption are we talking about? I have been carefully monitoring the oil consumption on my 2000 3.0i with 37000 miles on the clock, and it doesn't appear to use very much oil at all, certainly no more than my A class Mercedes.with only 9000 miles.on its clock. Since the last oil change around 3000 miles ago the level dropped from the top mark to midway amounting to around 1/2 litre. Is this considered normal?
Flight
User avatar
Southernboy
Joined: Thu 07 Oct, 2010 12:39
Posts: 6436

  Z3 roadster 3.0i
Location: Johannesburg

Re: M54 Oil Consumption - two possible fixes, which is better?

Post by Southernboy »

Considering the consumption on an M52 / TU motor is zero, that's a lot of oil being burnt in the combustion process. That means that after 37,000 miles, you have used an entire oil change in volume. As time passes this will increase as the oil rings wear. If you're burning that amount of oil, consider the volume by-passing the piston rings and being re-cycled by your CCV and dumped back into the sump. If you know how BMW engine cylinders are lubricated you can understand how much oil is passing through the rings. The cylinders are lubricated by jets underneath the the pistons. These jets squirt oil upwards into the cylinders. The piston travels downwards, and should pull the oil back down into the sump by the oil rings. If this is not being done efficiently, oil is left behind above the piston and becomes part of the "mix" on the next ignition / power stroke. Add to that the oily air being passed into the intake by the CCV system and you can imagine how much power you are losing because the combustion of fuel / air is inhibited by oil.
A quick check on the general health of your intake manifold is to remove the DISA valve ( 2 x torx screws) and have a look feel into the manifold. If it's oily you will appreciate that's the stuff being sucked into the combustion mix 3 or 4000 times a minute on the motorway..
"Normal is overrated"
Image

Z3 Upgrades and Additions
Post Reply