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demystifying the issue of carbon build up on valves.
I have a 2013 R56S (N18) and learning more here and elsewhere all the time.
I'd like to make sure I'm clear about what changes occurred in the post-2011 N!8 and how that affects coking of both the turbo and the intake valves. In particular, I want to understand how carbon can still build up on the intake valves. I'll start with some assumptions, then to my question.
1. As a direct injection engine, the fuel itself never contacts the back of the intake valves, that is air only. Except, as I understand it, on the 2011+ N18s, MINI re-routed what used to be a visible hose going from the left side of the valve cover into the intake and re-routed the channel so that blow-by dumps right into the intake through some channel within the valve cover.
2. The other source for particulates that could "carbonizing" on the back of the intake valves is from the turbo, which has the remaining PCV hose attached to it.
If all that is correct, the only way to minimize carbon build-up on the back of the valves is to reduce the particulates in the turbo input stream by using a catch can. There is no way to capture the other blow-by going directly to the intake.
Net out, install a catch can if you like to prevent crud from going ot the turbo and downstream to the intake -- might help to some degree. But...one will always have "dirty air" coming from the now-hidden second PCV output going directly to the intake (on 2011+ N18s only).
Is all that engineering correct?
If so, that -- more any any anecdotes -- would tell me what to do.
-I've read a few tech-heavy articles on this subject. Oil in the intake stream isn't the only source of carbon on the valves. The VANOS, under certain operating conditions, will open the intake valves early thereby allowing exhaust gases into the intake ports. These gases contain unburned hyrdrocarbons which contribute significantly to build up on the valves. Engine designers have spent a lot of time optimizing the burn in the cylinder to make it a clean as possible and allowing the "right amount" of exhaust into the intake ports to minimize carbonization. Build-up on valves was much more problematic on early DI engines compared to new ones today.
-Oil in the intake, combined with the hot exhaust gases as described above, contributes greatly to carbonization compared to not having any exhaust gases in the intake port.
-While I'm not intimately familiar with the N18, BMW engines typically have some type of oil coalescing feature in the crank case venting system to minimize oil in the intake and negate the effectiveness of a catch can.
-The turbo isn't a significant contributor of oil in the intake - assuming it's working correctly.
Nothing of note to add here except to say how I was taken aback recently when at a junkyard and saw a 2009 R56 that someone had removed the head from,
the crusty condition of the piston tops was astonishing, so much so that I snapped a pic...
...of course,
I'd suspect that primarily exists due to very poor maintenance as much as anything else?
-While I'm not intimately familiar with the N18, BMW engines typically have some type of oil coalescing feature in the crank case venting system to minimize oil in the intake and negate the effectiveness of a catch can..
I have considered a catch can for my N18 but have not been convinced it is needed. Would be very interesting to know what changes where made in the crankcase on the N18 vs N14.
I have considered a catch can for my N18 but have not been convinced it is needed. Would be very interesting to know what changes where made in the crankcase on the N18 vs N14.
Regarding your catch can, I was able to dig this up which seems to indicate it's totally not worth it.
The N13/N18 engines have an oil separator built into the valve cover, #2. Blow-by gases come up through #9, go through the separator and then take one of two paths depending on whether the turbo is producing boost or not. Under boost the gases escape through #12 and go to the intake duct upstream of the turbo, where there's enough of a vacuum generated by the turbo to pull them through.
Under non-boost, the check valve at #12 remains closed and all the gases go through 1, 5 and 6 which feed directly into the intake ports.
So if you install a catch can it will do absolutely ****-odd 90% of the time. The other 10% (under boost) it will only serve to catch the very small amount of oil the separator missed.
looks like a catch can to me right in the valve cover. I agree meth will keep the intake valves clean but that’s another story and comes with it’s own issues.
The BIGGEST difference between the Nq4 and the N18 engine is the addition of VANOS on the intake cam in the N18 engine. The N18 has the ability the vary the intake cam phasing and lift, and the throttle plate is only used for engine warmup. During normal operation of the N18 engine, the intake manifold has minimal vacuum, which means the PCV system had to be redesigned to accommodate that operation. That diagram show the engineering that went into making the N18 PCV system and oil separation system, and show very well why a catch can on the N18 is useless.
The BIGGEST difference between the Nq4 and the N18 engine is the addition of VANOS on the intake cam in the N18 engine. The N18 has the ability the vary the intake cam phasing and lift, and the throttle plate is only used for engine warmup. During normal operation of the N18 engine, the intake manifold has minimal vacuum, which means the PCV system had to be redesigned to accommodate that operation. That diagram show the engineering that went into making the N18 PCV system and oil separation system, and show very well why a catch can on the N18 is useless.
I think you meant Valvetronic not VANOS in the first sentence.
I think you meant Valvetronic not VANOS in the first sentence.
Right I’m sure he was referring to valvetronic as vanos cannot change valve lift. Valvetronic probably has the greatest affect on the valves staying clean it seems.
I have a baffled oil catch can but still worried about this. Seafoam is for primarily 2 stroke engines. any good solutions you can run to get this crud out?
The N13/N18 engines have an oil separator built into the valve cover ...
What is the source for this (that the above information applies to the N18 engine)?
Note:
a. the above graphic does not show an N13/N18 engine (just FYI, this means nothing in regards to whether the information applies to any one engine).
b. BMW/MINI in Germany quote exactly the same price for valve covers for N12, N14, N16 and N18 engines: € 313.70 (with the N12 and N16 sharing the same part). If the valve cover for the N18 had such an oil separation mechanism, I'd be very surprised if BMW didn't price it higher than those for N12/N16 and N14 engines.
Thanks for the link to forumbmw.net, very informative!
I should have phrased my question better:
Your mrbean's post suggests that the N13/N18 have an oil separation mechanism which the N14 (if not also the N12/N16) lacks (and thus an oil catch can makes sense for the N14 engine but not the N13/N18).
Is there any information available that shows this (i.e. that the N13/N18 is separating oil fumes in a way the N14 does not)?
PS.: I didn't claim that the valve covers are the same, just because they are priced the same. I meant to say that them being priced exactly the same, it would surprise me if one of them comes with such a feature while the others do not.
Last edited by giorgos; Dec 3, 2021 at 07:34 AM.
Reason: Corrected reference to post in question
The N14 and N18 engines have more differences besides the cam covers. The N18 has the variable intake valve lift and phasing, which the N14 does not have. The N18 operates with almost zero intake vacuum, whereas the N14 has typical intake manifold vacuum. (-18 inHg vacuum) The manifold vacuum, or lack thereof, would certainly change how the PCV system works, and how the cam cover would be designed. The revised flow path in the N18 cam cover is likely a result of the need to create vacuum in the PCV system for proper operation.
The engine revision was possibly also due to the horrible carbon fouling of the N14 design... but, that is speculation on my part.
