Question: You missed an answer to the "Black Oil" question in the July/August 2011 issue when you responded to the reader asking about his diesel engine oil turning black so quickly after an oil change. The 2008 6.6-liter Duramax uses EGR and recirculates a considerable amount of its exhaust back into the engine for reburning. The engine oil turning black almost immediately after an oil change is perfectly normal. Unless I'm mistaken, the 1994/1995 Cummins has no EGR system, so it doesn't recirculate exhaust back into the engine as they do now.
Good catch. I mentioned the different technology used in current production diesel engines, instead of those built 10 or 15 years back, as possibly having an effect on our reader's Duramax oil. And yes, EGR may be a direct link to the darker oil. EGR stands for "exhaust gas recirculation," and has been used in gas engines for many years. The system mixes a controlled amount of exhaust gas with the air/fuel mixture entering the combustion chamber. The reason behind EGR is its ability to lower combustion temperatures, therefore reducing harmful oxides nitrogen (NOx) emissions to the atmosphere. In response to the EPA's implementation of more stringent emissions regulations on diesel engines, engine manufacturers are using EGR and particulate filters, and selective catalytic reduction, to meet the new standards. In turn, specific diesel oils are produced to adapt to the higher demand. These oils are attempting to maintain current oil change intervals, while limiting any adverse effects on engine longevity.
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