It seems it is generally accepted that driving hard will help and I have agreed with that probably due to my experience in earlier years with carbureted/non-electronic vehicles. I have heard others say that with modern vehicles, it really doesn't help. I wonder which is true. Logic tells me that that at higher RPMs the engine gets hotter and is more likely to burn off deposits, but it also seems that the more aggressively you run your engine, the more crud will be emitted from the crankcase into the combustion chamber. Anybody else have an opinion on this?

 

This is not just my opinion it's fact, so here goes:

The N14 engine thrives from being driven hard, the faster the piston mean speed, (RPM) the more heat generated in the cylinders resulting in better thermal expansion and less blow by to contaminate the crankcase (crankcase pressure) from efficient cylinder sealing of the cylinder wall to piston ring, that said, although we have high RPM and efficient sealing from greater thermal expansion, and less combustion blow by, we still have crankcase pressure albeit the majority is now produced by the rotation of the reciprocating mass (crankshaft, connecting rods and pistons)

The same above ^^^ happens in the N18 engine too, the difference is all in the cylinder head valve train components, so with the basics of crankcase pressure out the way, let me explain the valve train geometry between the N14 and N18 engines:

The N14 has single vanos (timing control) on the inlet camshaft only and has a fixed amount of valve lift (9.5mm) from idle to red line, this fixed amount of lift allows full open flow of crankcase pressure oil mist contamination to be carried through the intake tract, and as previously mentioned the faster the piston mean speed (RPM) the greater the combustion sealing efficiency, less heat = less combustion sealing.

The N18 has dual vanos (timing control) on both the inlet and exhaust camshafts, furthermore there is variable valve lift control on the inlet camshaft, this controls the amount of valve lift, this ranges from 0.2mm at idle through to full valve lift 9.5mm at 4,500-6,500RPM, what we need to understand now is that unlike the N14 engine, the N18 will create more oil mist contamination at high RPM due to the variable valve lift control system allowing full 9.5mm valve open lift, so the best optimum oil mist contamination control for the N18 is low RPM with minimum valve open lift, this is the exact opposite of the N14 engine!

 

Wow! So I shouldn't feel badly about being in the throttle all the time with my N14 - I like that.

That explanation was little beyond what I can realistically comprehend, but I get the general idea. What's your background/how do you know this stuff? Know that I'm not doubting you, but it sounds like you do more than turn wrenches and I'm just curious.

 

Thanks CZAR for the excellent explanation.

Is it also fair to say that for either instance, N14 or N18, that even if one is "on it" as much as possible without abusing the engine, or one "takes it easy" without creating a road hazard as in the N18, that the problem is going to manifest itself anyway and that there is really not much that you can do to alleviate the problem?

Is the chance of making any significant difference worth it to drive in these exaggerated manners? Or do you just drive like you normally do and resign yourself to spending the money when it becomes necessary?

 

So this means that I shouldn't take my N18 over 2000 rpm, run it on the track, do autoX, pass cars on the back roads, use the sport button and generally have the fun that these cars are made for? This, I doubt, is the intent that BMW was aiming for when they redesigned the engine.

So please explain why "being driven hard, the faster the piston mean speed, (RPM) the more heat generated in the cylinders resulting in better thermal expansion and less blow by to contaminate the crankcase (crankcase pressure) from efficient cylinder sealing of the cylinder wall to piston ring, that said, although we have high RPM and efficient sealing from greater thermal expansion, and less combustion blow by" doesn't apply to the N18 engine.

Also, how is it that all of the above posts by N18 owners cite nothing in the OCCs. I doubt that they all drive like old ladies.

I don't doubt how you say the dual vanos works but somethings just don't add up in your conclusion - "so the best optimum oil mist contamination control for the N18 is low RPM with minimum valve open lift, this is the exact opposite of the N14 engine". Your own statement - the heat, expansion of piston and rings, etc - has to apply the same to both engines, so the N18 shouldn't be any worse than the N14 at high RPM. Wouldn't that mean that the N18 that the engine, which you say is better off with the dual vanos which helps at low RPMs, should still benefits from being run at higher speeds and is actually the best of both worlds? That is, an N18 can be driven at any RPM with little fear of carbon buildup that is any worse (possibly better than) than an N14 that is just driven hard. It seems that is a more logical conclusion from what you say.

 

Enjoy your N14 engine, use it or loose it, my background is 30 years this year of practical Motorsport engineering and component deign, I've also been raised within a family who have been and still are active in Motorsport, since the heady hay days of the 1930's, I still turn wrenches however only for the love and not for payment, those days are well and truly behind me.

Sadly in the both N14 and N18 engines there will always be an issue of carbon deposit build up on the backs of the inlet valves, that said, the N18 is and will be more forgiving due the variable valve lift control of the inlet valves, reducing the amount of cylinder vacuum draw required to fill the combustion cylinder, this reduction of air volume has a direct effect on the amount of crankcase contaminated vapour that is drawn through the internal PCV system, and subsequently into the inlet air runner tract.

No it doesn't mean you shouldn't use any more than 2000RPM let's see if I can clear things up for you, you've grasped that the N14 has a fixed amount 9.5mm of inlet valve lift whether this be at idle or 6,500RPM it is a set constant, therefore the cylinder filling volume is also constant.

Now lets look at the N18 it has a variable amount of valve lift throughout the entire RPM range, 0.2mm of inlet valve opening lift at idle through to 9.5mm maximum inlet valve open lift from 4,500 all the way to 6,500RPM this variable regulates the amount of cylinder vacuum draw and cylinder filling volume, this variable has a direct result on crankcase pressure due to low cylinder filling volume (pressure) at low RPM, this reduction in cylinder pressure further reduces the firing pressure resulting in less initial cylinder pressure blow by, therefore we don't need to produce extra heat to have efficient sealing between the piston rings and combustion cylinder wall/s as we have reduced the overall firing pressure.

Now as we increase RPM in the N18 we also increase inlet valve opening lift, whilst increasing vacuum draw and the need to increase cylinder filling volume, and if you've understood the above ^^^ then you'll know what happens next!

 

I live in muggy South Carolina, and my OCC needs to be emptied about every 2 weeks if it's been damp out. When I emptied it last week I got 160 mL of liquid, and after settling for a couple of days, 20 mL of that was oil. Some of that oil would now be coked onto my valves without the OCC. That said, now that my warranty is gone, I'll be installing water/meth injection.

Jon

 

You have an N14, not an N18, correct?

 

Yes......and I'm glad to see that the N18 design MAY have solved the problem. I'd love to see a diagram comparing the two PVC systems and how the new design keeps oil vapor out of the intake.???

Jon in SC

 

The N18 engine PCV system hasn't solved the problem, of carbon deposit build up on the backs of the inlet valves, all that happens is the variable valve open lift control system, significantly reduces the amount of air and subsequently vacuum draw to fill the combustion cylinder, resulting in extending the time before any significant amount of carbon becomes an issue, as the majority of driving tends to be in the low to mid RPM range.

 

Mmmmm - to paraphrase - both will have some amount of valve carbon build up, but the N18, overall, is better, no matter how you drive it. That's good to know as I am think signing up for my first track day of the season and I would hate to have to limit my engine to 2000 rpm; that wouldn't get me to 60 on the back stretch of WGI

Now a more broad based, related question - Is this an issue for all DI engines? Or has MINI/BMW missed the mark on this one?

 

It's an issue that will affect all GDI (gasoline direct injection) engines, the only way to combat the excess build up is to reintroduce port injection (as Toyota/Lexus have) to work in synchronised relation with the DI (direct injection) system, using the time proven method of passing fuel (gasoline) into the otherwise dry air intake found on GDI engines to wash the inlet port tracts and inlet valves, keeping the excess carbon build up to a controllable minimum.

Water/meth injection will help keep carbon build up under control too, that said don't expect to install water/meth on your already heavily coked up inlet tract and inlet valve carbon issue, and for it to rid you of the build up, this won't happen, to get the best results from a water/meth installation, have a de-coke first.

 

First of all, thanks for all your knowledgeable information on this issue. For the first time, I'm beginning to understand, from a layman's viewpoint, what all is involved with this.

I read somewhere that another manufacturer (maybe Toyota/Lexus) had the combined port injection and direct injection system. I'm wondering why all manufacturers including MINI didn't do this instead of just going to DI. I bet the buildup issue has cost MINI a fortune for the walnut shell blasting that they have paid for. I'm sure there must be some drawbacks...maybe cost, maybe fuel economy, maybe it was just lack of foresight on MINI's part.

 

This has probably been covered here, but I could not find it; does the 2013 Factory JCW still have the N14 motor, or does it now use the N18. I looked at the factory site and the horse power rating is the same as before.

 

The 2013 JCWs have the N18 engine. I don't think the power rating changed, although the window sticker mpg increased.

Link to Motoringfile article: World Premier 2013 JCW MINIs

 

What about the root problem, engine vapors in a dry intake system. Can they be routed somewhere else? It is an emission device. I am not all for disabling emissions but this one harms the engine and i am not cool with that. Where does the pcv hose connect? Is it in front of the turbo? I'm new to the Mini scene but have been doing engine stuff a long time. We need to talk about the problem because it appears that nothing so far can solve it as is.

I am about to order a MCS and all of this is disheartening, especially since BMW/Mini will not take responsibility for a design defect. Is there another thread that speaks of disconnecting the hose from the intake system?

 

On the 2011 and newer MINIs they did a redesign of the heads and Engine Control Unit. The PCV lines to the intake ports is now internal to the head. With the new dual vanos system, and changed variable cam timing, the carbon build up problem is greatly reduce and maybe eliminated.

I haven't read of any newer MINIs with the N18 engines having a carbon build up problem.

Dave

 

This is probably the Mother of controversial MINI topics. The main thing to remember is that almost everything you read is just peoples opinion and conjecture, including anything I say. Some will swear that an OCC doesn't work, others that it will solve all your problems. The same opinions exist about water/meth injection. The jury is still out on the N18 design, but it shows promise...time will tell. Then there's Seafoam, but that's a really big stretch. What I would love to see is an OCC installed on a new or freshly cleaned engine, and what the results are 40k miles down the road(same with water/meth, same with the N18). The only proven solution for the problem is physical cleaning of the valves as needed (but what about the crud that's also probably sitting on top of the pistons?). At least, if you're planning to buy a new MINI and carbon buildup causes a problem during the Warranty period (or does MINI consider this a Maintenance item?), they will do the cleaning for you. There are about a bajillion threads out there on this and related subjects. Welcome to the rabbit hole.
https://www.northamericanmotoring.co...uestion-2.html

Jon in SC

 

Another thing to think about is the area of the country that you live in. I have an N14 with a catch can. In the winter months I get about 6-8 oz of water per week (250 miles per week). I assume that most of this comes from the engine cooling down and drawing moisture into the oil and engine. I think that it would bother me knowing that this much water would go through the PCV system without the OCC.

I would think that the same concept would apply for the N18 as well. I agree that the N18 has design improvements over the N14, and that there has been little conclusive evidence of heavy carbon or lack of carbon on the N18.

Just trying to give another way of looking at the issue. In my point of view, $200 on a $20k car is a minimal investment if you think that there is any chance of improving the issue.

Mike

 

It isn't just BMW/Mini, ALL direct injected engines have this issue to greater or lesser extent. Just go check out the Audi forums, or google "audi direct injection carbon build up".

It looks like the N18 is a lot better than the N14 for carbon build up. While I'm considering adding an OCC to mine, I'm also aware that at some point I'll need to have the valves cleaned, and I accept that. Meanwhile I'm enjoying driving and modding my Mini.

My thoughts on those who let their PCV vent to the environment are documented in the other thread on OCCs.

 

At some point you need to take a chance. New MINI for 2014 with a new series of engines, you can hope that they are better than the existing. Or you can order the car the way that you see it now, with the issues that are discussed here.

If you are really nervous, you could see if the extended warranty would make you sleep better.

Mike

 

I want to get in before the 2014. I have had bad experiences with first year models and I do not want to wait 2 or 3 years after that.

 

I wanted to throw a shout out to Czar, who made a believer out of me with his explanation of hard driving's effect on carbon build-up. I'm now a believer. Of course it would be hard to prove it empirically without a controlled test, which none of us are about to conduct, but I believe, baby!

 

I put 100K miles on an '07 MCS and then finally bailed on it a month ago after spending more on maintenance and repairs last year than I ever spent on a year of loan payments to own it outright.

Long story, but I ended up trading it in for a new '12 JCW Coupe. It was an incredibly irrational decision to get back into another Mini after my history of issues with the '07, and believe me, I experienced EVERY typical problem including plunking down $800 on the walnut blast at 70K miles.

In the end I convinced myself that the N18 engine will address two of the bigger issues -- the timing chain and the carbon build up. And that I will be more vigilant about monitoring and changing oil than the owners manual told me to be on my first Mini.

 

I agree. Great explanation that even a non-technical person like me can understand. I also appreciate Helix13mini's posts and the expertise they show.