Carbon build up
01-04-2009, 06:52 PM
#21
Senior Member
Join Date: Dec 2005
Posts: 8,364
Likes: 0
Received 0 Likes
on
0 Posts
Scott, what's your point?
You can't possibly make the assumption that engine oil is the cause of this kind of acute carbon deposit problem.
Work with me here, buddy,...I'm on your side.
Work with me here, buddy,...I'm on your side.
01-04-2009, 06:57 PM
#22
AudiWorld Senior Member
Join Date: Jul 2002
Posts: 641
Likes: 0
Received 0 Likes
on
0 Posts
The modern cold start is very complicated, cat warm up and emissions etc
I would like to read about it actually... alternate cycle fuel mixtures?
I don't think a comparison to an old carb engine is relevent, fuel condensing in the intake for one makes for rough running for those.
I don't think a comparison to an old carb engine is relevent, fuel condensing in the intake for one makes for rough running for those.
01-04-2009, 09:12 PM
#23
Senior Member
Join Date: Dec 2005
Posts: 8,364
Likes: 0
Received 0 Likes
on
0 Posts
Sounds like you may been listening to looney theories
about oil vapor causing this acute carbon problem occuring in 2k miles???.
That's almost impossible. Stop listening to Scott's left field logic, it's nonsense. Sorry Scott, but it really is, period, END OF STORY!!!!!!!!!!!!!!!!!!!
That's almost impossible. Stop listening to Scott's left field logic, it's nonsense. Sorry Scott, but it really is, period, END OF STORY!!!!!!!!!!!!!!!!!!!
01-04-2009, 09:23 PM
#24
Senior Member
Join Date: Dec 2005
Posts: 8,364
Likes: 0
Received 0 Likes
on
0 Posts
That's pure nonsense, get with it please...
geez, Scott, listen to what you're saying, it's indefensible. Are you just being obstinate or what? This is just automotive insanity.
Sometimes I think you're just fu*cking with people here. The question is why.
Quite frankly, I'm so tired of this kind of nefarious discussion with someone who throws out 99.9% of established and accepted automotive fact to support his own pet theories.
Sometimes I think you're just fu*cking with people here. The question is why.
Quite frankly, I'm so tired of this kind of nefarious discussion with someone who throws out 99.9% of established and accepted automotive fact to support his own pet theories.
01-04-2009, 10:43 PM
#26
AudiWorld Expert
Join Date: Dec 2000
Posts: 33,078
Likes: 0
Received 0 Likes
on
0 Posts
All i see is theory. Why not run a catch can and see what happens?
"Especially in the area of the intake valves, the deposits originate from blowby gases and from internal and external exhaust gas recirculation, and in this process, the blowby gases and the recirculated exhaust gas come into direct contact with the intake valve."<ul><li><a href="http://www.freepatentsonline.com/6866031.html">Or, if you insist on continuing to be a keyboard tuner, read this.</a></li></ul>
01-04-2009, 10:52 PM
#27
AudiWorld Expert
Join Date: Dec 2000
Posts: 33,078
Likes: 0
Received 0 Likes
on
0 Posts
the whole point of evap/EGR systems is to circulate blowby oil back into the crankcase
unburned fuel evaporates and most of it gets burned when it re-enters the combustion chamber (but a certain percentage of unburned fuel obviously ends right back into the egr/evap system). On the way back into the combustion chamber, any non-volatile hydrocarbons (from oil) carried along stop off at the intake valves, and coke there from the heat, leaving deposits
I'm pretty sure this isn't theory; thats basically where most carbon buildup comes from. Whether or not different oils make a difference is definitely beyond my expertise.
Again, it would be easy enough to ditch the evap/PCV system and try one (or several) catch can(s) and see how much oil ends up in them, and if the valves end up cleaner.
Also, perhaps a water/meth system might help.
I'm pretty sure this isn't theory; thats basically where most carbon buildup comes from. Whether or not different oils make a difference is definitely beyond my expertise.
Again, it would be easy enough to ditch the evap/PCV system and try one (or several) catch can(s) and see how much oil ends up in them, and if the valves end up cleaner.
Also, perhaps a water/meth system might help.
01-05-2009, 06:25 AM
#30
Fuel dilution 101
Arthur, there are three basic mechanisms for fuel dilution of the oil.
1) Overnight some amount of fuel condenses in the cylinders and drips down through the rings and into the oil sump.
2) During cold start, the low tension rings in the engine do not seal well, and the overly rich mixture used until the car warms up, causes fuel to pass by the rings and into the sump.
3) Under normal operation, some of the spray from the high pressure injectors hits the cylinder walls, condenses and runs down into the sump.
Probably a combination of all three is at work in this engine, but is definitely correlated to cold starts and to times when there is high fuel delivery. However, the engine (as are all Audi engines) is designed to reduce the total average amount of fuel dilution in two ways. First, there is an oil/water intercooler that is designed to bring the engine up to operating temperature faster, and to keep the oil at 200 F or higher. This accelerates volatilization of the fuel from the oil, and forces it to be recycled through the PVC system. Second, in the PVC system there is a cyclonic separator that is designed to cycle oil back into the engine and allow fuel to pass back through into the intake.
The largest amount of fuel in the oil will occur when you do short cycle driving where the engine never comes up to full operating temperature. The rate of fuel entering the oil is greater than the rate of fuel evaporating from the oil, causing the percentage of fuel in the oil to increase over time. This can be mitigated by driving for a period of time at normal operating temperatures, in which case fuel will begin to initially evaporate faster than the rate of fuel entering the oil, and the average fuel level in the oil will reduce. As the amount of fuel in the oil reduces, the vapor pressure reduces, thus reducing the rate of evaporation. Eventually the rate of evaporation matches the rate of fuel entry in the oil, and the percentage of fuel in the oil roughly stabilizes.
As a result, the worst case fuel dilution at any time can range up to between 3% and 5%. If you were take very short trips and never let the water or oil get up to operating temperature, and then sampled the oil, you'd find a very high percentage of fuel in the oil. As a reference point, 5% fuel in this sump is equal to 1/2 Quart, so not an insignificant amount at all. But, if you let the engine run for 10-20 minutes, the excess fuel will burn off, and eventually the fuel/oil system will reach homeostasis, with 1% to 2% fuel in the oil, or about 0.1 to 0.2 quarts.
Even though your dipstick says the oil level has not changed, because of the amount of fuel that has been placed in the oil, this has to happen through an exchange mechanism, where the oil has been replaced by the fuel, and has burnt off. Otherwise, the measured oil level would rise. Fuel contains some wicked solvents like benzene and hexane which will dissolve some of the oil components and carry them off through the PVC system. Those solvents can also dissolve the ZDDP anti-wear layers that are built up on the bearings, unless protected in some other way. This is why iron wear, in particular, increases in engines with fuel dilution, and why oil gets carried into the intake and deposits on valves.
1) Overnight some amount of fuel condenses in the cylinders and drips down through the rings and into the oil sump.
2) During cold start, the low tension rings in the engine do not seal well, and the overly rich mixture used until the car warms up, causes fuel to pass by the rings and into the sump.
3) Under normal operation, some of the spray from the high pressure injectors hits the cylinder walls, condenses and runs down into the sump.
Probably a combination of all three is at work in this engine, but is definitely correlated to cold starts and to times when there is high fuel delivery. However, the engine (as are all Audi engines) is designed to reduce the total average amount of fuel dilution in two ways. First, there is an oil/water intercooler that is designed to bring the engine up to operating temperature faster, and to keep the oil at 200 F or higher. This accelerates volatilization of the fuel from the oil, and forces it to be recycled through the PVC system. Second, in the PVC system there is a cyclonic separator that is designed to cycle oil back into the engine and allow fuel to pass back through into the intake.
The largest amount of fuel in the oil will occur when you do short cycle driving where the engine never comes up to full operating temperature. The rate of fuel entering the oil is greater than the rate of fuel evaporating from the oil, causing the percentage of fuel in the oil to increase over time. This can be mitigated by driving for a period of time at normal operating temperatures, in which case fuel will begin to initially evaporate faster than the rate of fuel entering the oil, and the average fuel level in the oil will reduce. As the amount of fuel in the oil reduces, the vapor pressure reduces, thus reducing the rate of evaporation. Eventually the rate of evaporation matches the rate of fuel entry in the oil, and the percentage of fuel in the oil roughly stabilizes.
As a result, the worst case fuel dilution at any time can range up to between 3% and 5%. If you were take very short trips and never let the water or oil get up to operating temperature, and then sampled the oil, you'd find a very high percentage of fuel in the oil. As a reference point, 5% fuel in this sump is equal to 1/2 Quart, so not an insignificant amount at all. But, if you let the engine run for 10-20 minutes, the excess fuel will burn off, and eventually the fuel/oil system will reach homeostasis, with 1% to 2% fuel in the oil, or about 0.1 to 0.2 quarts.
Even though your dipstick says the oil level has not changed, because of the amount of fuel that has been placed in the oil, this has to happen through an exchange mechanism, where the oil has been replaced by the fuel, and has burnt off. Otherwise, the measured oil level would rise. Fuel contains some wicked solvents like benzene and hexane which will dissolve some of the oil components and carry them off through the PVC system. Those solvents can also dissolve the ZDDP anti-wear layers that are built up on the bearings, unless protected in some other way. This is why iron wear, in particular, increases in engines with fuel dilution, and why oil gets carried into the intake and deposits on valves.