Condition of oil before 2nd oil change?
- Thread starter dsm918
- Start date
FMOS Racing
Member
- :
- 2008 MS3, plus a pickup and a beater car
Rich-running turbo car, oil turns black pretty quickly. Just means it's doing its job. 
thank you for confirming my findings. i also think that the oil turns too black too quick, and i'm still waiting to hear a good technical explanation. all i've heard is 'that means the oil is doing its job.' yeah...but why is the oil in a honda barely amber color after 3k miles, when in the MS3 it's pitch black after the same miles?
i'm guessing it has something to do w/ the engine running overly rich, or the DI atomizes the fuel to finer particles, creating more soot, or that the filter doesn't contain enough filtering material to properly clean the oil. i had a diesel car for 2 yrs, and it did the same job on the oil- black as midnite in a coal mine after barely 3k miles...(wow)
i'm guessing it has something to do w/ the engine running overly rich, or the DI atomizes the fuel to finer particles, creating more soot, or that the filter doesn't contain enough filtering material to properly clean the oil. i had a diesel car for 2 yrs, and it did the same job on the oil- black as midnite in a coal mine after barely 3k miles...(wow)
FMOS Racing
Member
- :
- 2008 MS3, plus a pickup and a beater car
One of the purposes of motor oil is to contain and isolate combustion byproducts. When a vehicle runs rich, as is the case with the MS3 or a diesel, there are excess combustion byproducts (soot).
If the oil is black, the soot is staying in suspension and that's the oil doing its job.
The soot particles are far too small (they're carbon molecules and are smaller than the long chain viscosity improver - vi - molecules in the oil) to be filtered and do not pose a danger to the internals of the engine.
The coefficient of friction of soot-contaminated oil actually DECREASES as the soot content rises - that's because of the dry lubricating properties of carbons (e.g. graphite). However, at some point, the ability of the oil to form a protective film starts to decrease and shear and scuffing increases. The soot content (as a percentage of oil make-up) where the breakdown occurs is really pretty dang high, though, and nothing to worry about for typical oil change intervals.
[Edit] Tweaked the wording a little to make some things a little more clear, I hope.
If the oil is black, the soot is staying in suspension and that's the oil doing its job.
The soot particles are far too small (they're carbon molecules and are smaller than the long chain viscosity improver - vi - molecules in the oil) to be filtered and do not pose a danger to the internals of the engine.
The coefficient of friction of soot-contaminated oil actually DECREASES as the soot content rises - that's because of the dry lubricating properties of carbons (e.g. graphite). However, at some point, the ability of the oil to form a protective film starts to decrease and shear and scuffing increases. The soot content (as a percentage of oil make-up) where the breakdown occurs is really pretty dang high, though, and nothing to worry about for typical oil change intervals.
[Edit] Tweaked the wording a little to make some things a little more clear, I hope.
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