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post #1 of 964 Old 13th August 2005, 02:49 PM Thread Starter
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FAQ on Carbon Build-Up Issue (First Attempt)

The whole carbon build-up issue really needs a FAQ (IMO). I know it has been discussed on this board, but no strong consensus on the problem has been formed. Since I own a high mileage (106,000) car I worry about this, and everyone’s car is not getting any younger. After reading how much BMW wants to fix this problem ($8000) I really start worrying about this. I understand the labor hours to take the heads off this engine. If we M5 owners can find a solution or an exact cause of this problem we may head off the problems, headaches and expense of this gremlin. I was hoping to get the dialogue going again to try and answer some of the carbon build-up issues and further our learning.

After reading the several posts on this matter I will give it a try, please add, remove or modify the FAQ at any time. The information I obtain is directly from this M5board and I have no other sources of information. I was hoping we could contribute to factual data gathering

What exactly is the carbon build-up problem:
Quote from TetherM5 "The SES light came on, they changed the Secondary Air Pump and some O2 sensors. Carbon is blocking the exhaust system causing a low pressure fault on the secondary air system."

BMW cost to fix the problem: BMW has a protocol and handy parts kit to fix this issue. Cost approx $5000- $8000.00

What year models are affected: 2000 and 2001, may have hit a 2002.

What is the percentage of cars are effected by carbon build-up:
Don't know. Maybe an informal poll of everyone on the board and we can come up with an unscientific percentage value.

Is there any preventive maintenance or prophylactic procedure to prevent carbon build-up: Maybe several high-rpm (red line) runs will help blow it out. No one knows for sure at this time.

What causes the problem:
No strong answer on this question. It may be Oil consumption in older model m62's, bad gas, babying the car??? Please contribute.
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post #2 of 964 Old 13th August 2005, 05:23 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

this is just speculation, but i think this is similar to the problem porsche had with earlier 993's (i think that was the model). It's the smog pump passages in the heads that get blocked with carbon, so when the smog pump runs on the cold start, it can't blow enough air into the exhaust. There really should be a way to access this from outside the engine, i'd think, by going thru the smog pump passages, perhaps with a chemical, compressed air, pipe cleaners, who knows... It sounds like a design issue really, hard use may not do anything, depending on where these ports are. It would be nice to have some type of schematic of the head to see where we are really dealing with.

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post #3 of 964 Old 13th August 2005, 05:30 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

I think this is an issue with a lot of BMW engines, not just the S62. I seem to recall being told by a BMW tech that it happens when operating the car a lot at retarded ignition timing, which you get when most of your driving is in city, stop and go traffic. "Blowing it out" with periodic blasts might help some, but supposedly the only "prevention" is a driving style that routinely takes you to upper RPM (4-5k) and includes highway driving. There is a chemical treatment for a few hundred that they can do which doesn't involve removing the heads but I don't know how effective it is. That $8k solution is downright frightening!

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post #4 of 964 Old 13th August 2005, 05:34 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

I've HAD the heads replaced at 87,000 miles after repeated SES faults indicating the head - BMW replaced the parts and I payed the labor.

Something another poster said that has really helped since (although I've not had a SES light on since the replacement).

This poster said that the way to blow the carbon out was not by flooring it but rather run the car in a higher gear for an extended drive.

I've found that THIS has improved the running of the car much better than the short bursts often recommended.

You don't have to run the car for 500 miles either - after reading the thread, I ran the car in 3rd gear at 60MPH for about 15 miles and viola! - car ran better - NO doubt.

I cannot remember the poster's name but, he very well might be on to something.

Also, there was no difference in the weather coditions - it has been a very hot and humid summer - ALL summer here in NC.

You might want to try this.
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post #5 of 964 Old 13th August 2005, 10:09 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

Two other issues to ponder/add to the thread:

Is it a mileage issue or a MY issue? If it is mileage, then one would imagine the 2000, 2001s are the first to reach these mileages... only time will tell.

Signed, concerned at 33k

Does AutoRX or other fuel or oil additives/cleaners help?

Is there a BMW position for coverage under warranty- cpo or standard?
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post #6 of 964 Old 13th August 2005, 10:51 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

Originally Posted by mottati
this is just speculation, but i think this is similar to the problem porsche had with earlier 993's (i think that was the model). It's the smog pump passages in the heads that get blocked with carbon, so when the smog pump runs on the cold start, it can't blow enough air into the exhaust. There really should be a way to access this from outside the engine, i'd think, by going thru the smog pump passages, perhaps with a chemical, compressed air, pipe cleaners, who knows...
Perhaps this could be checked by running some laparoscope-like device into the air passage with the smog pump removed for a look-see. BTW, I concur totally with what tranck suggested above. When my M3 first saw extended storage some years ago, I fired it up and drove off but even at the end of a day's city driving it didn't feel really right. I then took it for a 10-minute run at a constant 4,500 rpm while holding it in third gear, and that procedure worked wonders...it felt like a new car. I've employed that technique ever since.

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post #7 of 964 Old 13th August 2005, 10:53 PM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

The best way to prevent carbon buildup is to drive the car hard and
with higm rpms.

Babying an M5 is just a waste of resourses. Switch it to an 540 instead.

3 times a day and you will have no problems with carbon

Last edited by Alexandar; 13th August 2005 at 10:53 PM.
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post #8 of 964 Old 14th August 2005, 01:59 AM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

The issue of carbon buildup in the entire head and cylinders compared to the issue that many people are seeing with the SES light coming on indicating a secondary air fault are similar yet two entirely different animals. There have been a couple posts with people who has had issues with the car suddenly running rough and the diagnoses being carbon buildup in the combustion chamber and exhaust ports causing the engine to run terribly - this seems to be a like issue but one that is much more inhibitive to the normal driving operation of the car. If there is excessive rich combustion during warm operation or significant oil blowby, the exhaust cylinder, piston, and exhaust ports become coated with heavy carbon creating an inefficient combustion and creating a rough running engine with predetonation issues, compression issues from a ring and valve seat contamination. Effectively the cleaning process is just as intense should you begin to have an engine that runs rough and throws codes for cylinder head temperatures, predetonation, etc.

In my case and several other cases the issue seems to be with the channels that allow the secondary air system to include additional oxygen into the exhaust ports during a cold start to provide the ability for the raw fuel to continue burning in the absence of engine heat. The SES light comes on when the computer recognizes a low pump pressure into the cylinder heads - sometimes it can be a bad pump, in my case it is the restriction created by the building of carbon over time. Permanent SES light unless the carbon is removed. The engine is going to run its most rich when it is cold and the idea I have about this issue is a flawed design that is trapping carbon during rich operation or during the ludicrous 1 ltr / 400-1000 miles that BMW claims was normal DURING the factory warranty period. I am one of those people who pushes about a litre every 1200 miles or so and it is my assumption that this, included with a poor exhaust porting design has lead to to this problem and will continue to cause issue with other M5's as they stack the miles on.

This issue has nothing to do about driving the car soft - it is bad design of the port channels / system that is particularly vulnerable to carbon contamination during cold start. I also feel that the cop-out of BMW to develop such a ludicrous standard of oil consumption normalcy has created additional carbon to buildup on the exhaust port system during hard driving (I use a heck of a lot more oil during race / high RPM driving then low RPM's.) This problem is not with driving the car soft - I am so tired of hearing that.

My extended warranty company has denied my claim for the $8K repair as they sight that buildup of carbon, varnish, etc is not a direct failure simply preventative maintenance an is not covered. There have been several people in here who have had the BMW CPO deny coverage as well which is downright crazy!

I am going to complete the Auto RX treatment for the next couple of months and hope my carbon issue does not suddenly result in an operation issue until the treatment can start dispersing the carbon. Who knows, the carbon might be so stacked up in the head it many be too late for a non-invasive procedure.
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post #9 of 964 Old 14th August 2005, 07:29 AM Thread Starter
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Re: FAQ on Carbon Build-Up Issue (First Attempt)

TetherM5 I feel you pain!!!!! You have some great information. I see some of the differences in your explanation, but why in your particular case carbon build-up attacks or clogs the channels for the secondary air system is the question. That is the huge question. If we were the doctor examining the patient we don't have enough data. What is different about your engine and why other are not effected and some are. Maybe its like the NiSiKL situation, some oil, gas, fuel injector cleaner, area of the country, or driving habit is causing this failure mode. There are so many quesitons to ask!!

Anyhow.. I have pondering whether or not to write about a little trick I use on my boat engines to get rid of carbon build-up. I have decided to write it up because it works for me, and I have been doing it for the past 6 years. I have thinking about how I routinely (1 a year) remove carbon build up in my boat motors. I have a boat with two 7.4 L (454) engines that consumes oil (50W). By mid season after running the boat hard for 30 to 40 minutes then immediately shutting down the engines will after-run (diesel on) where the ignition is shut off but the engine continues to run. Carbon build up is not the only culprit for engine dieseling but is part of the equation. Carburetor is another one. (To make this post short I will not explain why they diesel. Google it and you will find your information) DISCLAIMER: The following idea may be a stupid and you should try it at your own risk. A new 7.4 L marine engine is a lot cheaper than a M62. Another powerboat racer told me to mist a little water directly into the carburetor with the engines running. You don't want the engines to die and you have to keep them running after you do the treatment. The results are great, this slick of carbon flakes forms where the exhaust enters the water. The carbon flakes are not oily or have and refractive index to them, but just scales of carbon soot. After the treatment the engines run great and no more dieseling. I have been doing this once a year for 6 years now.

Now would I try that in my M5..... right now I wouldn’t, but if I were possibly in your case (constant SES, AutoRX failed, going to break down and pay BMW $8K) I might try it by (lightly) misting a 50% water/alcohol solution into the intake manifold and have someone monitor the backend and see what is coming out.. The other question is will the water or AutoRX treatment solve your particular type of carbon build up problem. It would probably just blow out all the carbon in the cylinders and valves.

Anyway these are all great post for updating the FAQ. I will update it shortly.

Also, TetherM5 I am most interested in the success or failure of your AutoRX treatment, as probably would most members of this board (IMO). This may be the magic M5 god cure.
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post #10 of 964 Old 14th August 2005, 11:13 AM
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Re: FAQ on Carbon Build-Up Issue (First Attempt)


You have started a very good thread!

I too have heard of using water spray to clear carbon.

I have one concern though: the catalysts. (I assume there are no catalytic converters on your marine engines?)

If the carbon build-up comes off in flakes, would that not clog the catalytic converters? Or ignite at the catalytic converter?

Perhaps the safer procedure would be to remove the exhaust system downstream of the headers and remove the top of the plenum chamber,
attach exhaust fume extractors at the headers (assuming the extractors can take the heat, otherwise attach steel pipes in between).

Then run the engine warm and apply water/alcohol to one cylinder at a time.

BTW, does anyone know if turbo engines with water injection get less carbon buildup?


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