FAQ on Carbon Build-Up Issue (First Attempt) - Page 19

wilsodh · 14th September 2005, 20:36

Quote:

Originally Posted by mottati

I also find that interesting. Especially when you consider that the M5 was available in europe in 99, so there is a larger number of older, higher milage cars with older design piston rings, so more oil consumption. 10/60 seems to be more widespread in the s62 in europe (they do not use 5.30, but do seem to use castrol slx, which i think is 0w30).
Mike

Kin Mak (Ireland) confirmed off-line that his car is at the high end of the oil-consumption spectrum (1L/300-500 mi). His early '99 build car has 50,000 miles of mostly low speed city driving (currently averaging 17 mph), and yet has not had a carbon build up fault. Kin Mak would seem to be a poster-child for bringing on the problem if the main issue is oil consumption (no offense Kin Mak!). We also have greg (CA) who's early '00 has 97,500 mi with consumption @ 1 qt/1000 mi, yet has not has a problem. greg alluded to a cleaner-burning gasoline in California in his poll response.

It is fascinating to consider these data along with Norgeiron (Honolulu), who had a verified carbon build up problem at only 17,000 miles. Just thinking out loud, but I find myself wondering more and more about the contribution of the gasoline quality to this problem. Maybe we should take a closer look at possible regional & geographic differences in gasoline formulations to better fill out the picture...

Cheers,
Dave

Kin Mak · 14th September 2005, 22:43

Quote:

Originally Posted by mottati

Keep in mind that US 93 octane (R+M/2) equals about 98 octane in europe. 95 is about 90 here, which is our 'midgrade' in most markets.
Mike

Hi Mike

Could you clarify that? How is our rating different from yours? Is is not a standard?

Kin

mottati · 14th September 2005, 23:02

Quote:

Originally Posted by Kin Mak

Hi Mike

Could you clarify that? How is our rating different from yours? Is is not a standard?

Kin

Hi Kin,
There are a couple of different 'octane rating systems' out there. In most of europe, you use the "research" octane number, RON. There also exists a "Motor octane number" which i've never seen used as a stand alone rating. In the US, to complicate things, we use the average of the two, hence my mention of (R+M)/2 so, in general, our octane rating at the pump is about 5 units lower than your posted RON. Our super unleaded for the most of the US is 93, in california the max you can find is 91. A few states have 94 as well.

Kin Mak · 14th September 2005, 23:04

Quote:

Originally Posted by mottati

Hi Kin,
There are a couple of different 'octane rating systems' out there. In most of europe, you use the "research" octane number, RON. There also exists a "Motor octane number" which i've never seen used as a stand alone rating. In the US, to complicate things, we use the average of the two, hence my mention of (R+M)/2 so, in general, our octane rating at the pump is about 5 units lower than your posted RON. Our super unleaded for the most of the US is 93, in california the max you can find is 91. A few states have 94 as well.

I see says the blind man...

Cheers for the clear up.

Kin

wilsodh · 15th September 2005, 17:09

Quote:

Originally Posted by mottati

Hi Kin,
There are a couple of different 'octane rating systems' out there. In most of europe, you use the "research" octane number, RON. There also exists a "Motor octane number" which i've never seen used as a stand alone rating. In the US, to complicate things, we use the average of the two, hence my mention of (R+M)/2 so, in general, our octane rating at the pump is about 5 units lower than your posted RON. Our super unleaded for the most of the US is 93, in california the max you can find is 91. A few states have 94 as well.

I haven't had a chance to look into this, but what do we know about gasoline additives; in particular, what makes a gasoline 'cleaner burning', as supposedly is the case for California gas. When refiners formulate with 'detergents', what really are these, and how do they contribute to less carbon buildup (as mainline oil companies like to advertise)?
Don't expect you to have all the answers, just thinking out load and downloading some of my own questions....

Cheers,
Dave

jaj · 16th September 2005, 05:52

First, a big vote of thanks for LLcoolM5 for his effort on documenting the problem and what he found when he literally dug into it!

If you think about the way that solid buildup arises, there are a few key points:

- it builds up in the pipe that links the valve and the two cylinder heads. Presumably the heads as well, but certainly the pipe.

- it's a mix of carbon and some sort of binder. Pure carbon is unaffected by xylene or toluene, so for it to slowly dissolve, there must be a "goop" that's actually holding it together.

- the only sources for the carbon and the binder are the fuel and the oil. The S62 runs rich most of the time, and most rich at large throttle openings. This is the most likely time for carbon/goop to be created and available to go into the passages and the cross pipe.

- the carbon/goop mix must get into the cross-pipe when the circumstances are right. It's unlikely that it gets there when the smog pump is running because it would have to flow against the compressed air current from the pump.

- logically, the carbon/goop mix most likely gets into the pipe when the engine is at full (or nearly full) throttle (so that it has exhaust back-pressure behind it) and the engine is warmed up enough that the smog pump is turned off.

- to get into the pipe, it would seem necessary that the flow control valve that cuts off the smog pump and isolates the two arms of the cross pipe would have to leak in order for the carbon/goop to flow into it. Otherwise air pressure in the plumbing held in place by the closed valve would keep it out.

The big question for LLcoolM5 (or Shadowman, or anyone else that's actually taken these things apart) then is "in your opinion and from what you've seen, is it possible that the whole problem is caused by a faulty control valve?"

I'm very interested in this whole issue!

Cheers
JJ

wilsodh · 21st September 2005, 18:41

Quote:

Originally Posted by jaj

The big question for LLcoolM5 (or Shadowman, or anyone else that's actually taken these things apart) then is "in your opinion and from what you've seen, is it possible that the whole problem is caused by a faulty control valve?"

I thought I'd give this thread a bump back to the fore since it has been sitting idle for a few days. I am having some discussion with a BMW trained technician (now independent) that might be helpful. I'll pass along any useful information.

As for the faulty control valve, it might help explain some divergent data (why some cars have the problem early on, while others do not). I wonder if the 'dead air' that would reside in the secondary air pipe between the head opening and the closed control valve would not normally be displaced (perhaps slowly) by the turbulence that goes on in the combustion chambers, even if the valve was working properly. Indeed, if combustion gases did find their way into the pipes, the relative lack of air flow combined with the lower temperature in the pipe might provide ideal conditions for carbon/goop condensation. But I'm just guessing...

Cheers,
Dave

DavidS · 21st September 2005, 20:17

Quote:

Originally Posted by jaj

- to get into the pipe, it would seem necessary that the flow control valve that cuts off the smog pump and isolates the two arms of the cross pipe would have to leak in order for the carbon/goop to flow into it. Otherwise air pressure in the plumbing held in place by the closed valve would keep it out.

The valve only isolates the smog pump from the tube. It does not isolate the two ends of the tube from one another. Therefor, when a differential pressure exists between the two heads exhaust gas will flow in the tube.

I wonder if cars with an X-pipe exhaust system are immune to this problem?
(The X-pipe connects the exhaust tubes from both heads together before the catalytic converters and thus lower the instantaneous differentil pressure between the heads.)

(In a previous post in this thread I have suggested adding two more one-way valves serving to isolate the two ends of the tube from one another.)

David

mottati · 21st September 2005, 20:32

Quote:

Originally Posted by DavidS

I wonder if cars with an X-pipe exhaust system are immune to this problem?
(The X-pipe connects the exhaust tubes from both heads together before the catalytic converters and thus lower the instantaneous differentil pressure between the heads.)

David

David the factory exhaust already has an H pipe type of crossover, so the exhaust should be ballanced. this is after the cats but before the resonaotors, same place the supersprint X pipe is installed.
Mike

DavidS · 21st September 2005, 20:41

Thanks, Mike!

I learn something new every day.

Then leakage in the valve isolating the smog pump from the tube seems the most likely reason for the exhaust gas flow into both ends of the tube.

David