Scare stories are surfacing everywhere about the buildup of carbon on DI engines, particularly like those used in the current generation of GM Gen-V DI engines used in many of their vehicles or the current generation of BMW engines. Turns out that the PVC oil separator doesn't separate oil as well as it should resulting in an oil mist entering the engine before the throttle body through the PCV manifold intakes. Evidence includes oiled-up throttle bodies and, now, a few pics of badly coked intake valves on 30,000-ish mile engines. It's too soon to know how GM intends to handle this since these engines have a nominal 100,000 mile power train warranty. (Which, interestingly, has been cut dramatically for the 2016 model year.)

Thus my question: has anyone hit the kind of mileage yet on any of these Valvetronic DI three- or four-cylinder engines in the 2014-15 Mini? Has anyone had evidence of intake problems such as rough running, poor idle, poor power? Anyone have and resolve the problem?

The GM truck people are now rushing to add "Catch Cans" in the PVC circuit. The purpose of these is to add another oil/water/air separator in the PVC line before it hits the intake manifold. According to *many* accounts of those who've installed them, they tend to accumulate an alarming amount of oil. Alarming in the sense that "you don't want to dump that into your intake", not so much as "this engine is using a lot of oil".

Maybe someone who has either encountered this issue, or knows how well BMW has avoided the problem by designing a really good PCV oil separator, can jump in here with some insight.

 

Catch cans do absolutely nothing for reducing the carbonization of the valvetrain. The only thing they'll do is reduce the amount of blow-by in the intercooler tract, and cause a lot of aggravation in winter months, as they accumulate condensation that will freeze and back up into the PCV system, and cause all sorts of problems.

The only thing that will help reduce valve buildup is water-methanol injection, or the port-injection of gasoline.

 

You know that they don't reduce carbon build-up exactly how? There are a whole lot of people who disagree with that notion, and who have some pretty good evidence to back it up. Not in MINIs of course.

If it's not oil burning, then where is the carbon coming from? Fuel never sees the backside of the intake valves, except for some swirl in the combustion chamber that might occur during the injection part of the cycle. The carbon buildups I've seen documented are MUCH larger than just the backs of the valves. They extend up the stem and around the port. So where is that coming from if not from PCV oil mist?

As long as you're not driving exclusively short trips, the cans reach approximately the same temperature as the oil and, in theory, evaporate the water back into the intake as they should.

My point here was not to sell catch cans, anyway. I don't have any, and have no plans to buy or install any. I was merely pointing that out as a "solution" being adopted by a lot of owners who are already seeing the effects of carbon on the intake valves in DI engines, just like the mess BMW had in its hands 30 years ago trying to use the unsuitable gas available at the time. And I'm wondering what's to stop the same thing happening on these engines aside from the much longer path that PCV emissions take to reach the intake manifold.

So let me repeat my question as we've already wandered off-topic: has anyone with a higher-mileage current generation MINI (or BMW for that matter) seen an unusual carbon build-up, serious enough to affect normal operation?

 

Maybe you should ask this question regarding N18 engines in '11-'13 R56S'. I had a '12S and never had a problem. The service manager at the dealer that sold me my '12S and '15S told me that the N18 engines were not coming in with the carbon buildup problems associated with the N14 ( '07S-'10S).

 

I'm asking about ANY Direct Injection BMW engine, including the current generation of turbocharged engines. Did the engines you just mentioned have Direct Injection? I'm not that familiar with them.

 

The N14 and N18 engines referred to are direct injection.

 

I have not heard of any N18 aka MINI motors made from 2011 on in most models having this problem. This topic has been around for years. The N14 DI turbo motors seemed to be the worse with most having to dr carbon valves around 70k.

In a side note I pulled my intercooler off at13k and there was NO oil or residue in it,most of the N14 had oil I them ,which apparently came from a poorly designed PVC system letting oil get into intake air stream.

 

Yes, both engines were turbo d.i. engines. While the N14 had a lot of problems, the N18 has been a very reliable engine. While you're asking about the new engines, I think it would help to see the evolution of direct injection. It's here to stay.

 

I had to have my 2010 S Hardtop with N14 engine intake valves walnut blasted twice within 24,000 miles.

 

The intake fouling problem and continued high maintenance was a determining factor in selling our 2009 cars.

 

I have 21,000 miles on my F56 triple and my intake valves are clean. It idles and runs great. No carbon or fouling on the plugs either. Take your worries back to the GM forums they are not needed here.

 

My 2007 MCS ran like a top until I traded it in 2014 at 77k miles. I heard about people having to have the intake valves blasted but not mine.

 

It just comes down to how good the PCV catch can system is. If it's good, then the cleaning interval is long. If it's junk [like 1st gen VW/Audi 2.0T FSI's], then it needs cleaning frequently.

 

My dealer recently hosted a Tech Day where we discussed this issue, among others. The newer engines are supposedly engineered to allow a bit of the combustion to lick around the edges of the valves before they fully close.

There was also a discussion that engines that are driven at lower RPMs tend to build up more carbon. Reminds me that my dad used his right foot to "clean the carbon out" of his Chevy V-8s from time to time. Loved that!

 

Aaaah, the time tested Ignorance Is Bliss approach! Looks like you may be a veteran practitioner!

 

What do you gain if the carbon issue continues with the new models? What do you lose if BMW have solved it?

I don't understand the motivation for the behaviour...

 

There are other DI motors out there. Some are handling carbon buildup better than others. VW and Ford are using them as well for example. I believe the VW forums have had this discussion.

As far as OCCs go. I don't agree that there is any proof they provide any benefit other than you can see that the can catches SNOT.

I had one on my JCW and removed it after a short time, when my valve cover started leaking. I was using the OCC and the PCV boost tap block. I have no proof, but I think the increased pressure started the leak on the valve cover, but I digress.

My actual point is that there has not been an actual study with a car in a controlled test using the OCC and not. Performing the same actions, in the same climate, with the same driver and style etc over a long term and then measure the difference in the buildup. As an example my JCW had 99,000 miles on it when I had the first walnut blasting done and while there was buildup the shop said they had seen much worse on cars with much less miles. Mine was an 09 N14 motor not the current platform that is offered.
https://vimeo.com/65613419

Even vendors on this site, that sell these items have said that there is no empirical evidence of their benefit. But owners want them and they are in business to sell and service so they sell them.

 

You're talking about generic aftermarket catch cans, not the integrated PCV vapor handlers within the valve cover, aka factory catch cans. They've been used in some form or another for decades now, but only more recently have they been more carefully CFD'd to minimize deposition with DI setups. There are plenty of SAE white papers on the subject, not to mention proprietary OEM R&D, but the general public is not privy to that information.

To your first sentence; the reason some engines inherently have cleaner valves comes down to how effective their built-in catch cans are. As each engine generation is developed, it can be reasonably assumed each OEM is making improvements, some more than others.

 

Because I've seen the valves of N18s compared to N14s at similar mileage and driving habits, and the N18 valves are nearly spotless.

FWIW, when I removed my intercooler recently, I found little to no oil residue in my intercooler or associated ducting. It's a sign of the upgraded PCV doing its job.

Additionally, the addition of variable valve timing to the exhaust valvetrain has proven to minimize carbon buildup, as well.

That being said, the only way to eliminate it completely is to have a hybrid injection system that washes something over the valves.

 

Bottom line, these engines are extremely durable. If a carbon cleanup is necessary at 120,000 miles, big deal.

 

Bingo.

Carbon cleaning is a necessary evil with DI engines - it's just a matter of soon it's needed. 100-120k is a perfectly reasonable interval. 30k is not.

 

Locking for Moderator review.

 

Thread cleaned, but I'm leaving it locked. This rehashes a topic we've got lots of information about already, and this went nowhere fast.

If anyone wishes to begin/rehash/whatever the topic, start a new thread if you must. Hopefully we can behave ourselves better the next time around.