Truck Trend Garage: 2008 Duramax Chevrolet Silverado 2500 Black Oil
Question: I had a 1994 and 1995 2500 Cummins Dodge diesel 4WD and changed the oil every 3000 miles using Mobil Delvac 1300 Super 15W-40 diesel-engine oil. The mechanic would always say how clean the drained oil was and that I was wasting my money. I purchased a new 2008 Duramax Chevrolet Truck/Silverado/2500 4WD. It now has 20,000 miles. The first time I checked the oil, it was black. I had it changed, using the same oil l mentioned above. Checked the oil a few days later, and it was black. I went back to the dealer and the techs couldn't explain why. Called several other dealers and no one could give me a reason, some saying not to worry because it's under warranty. I was unable to find a phone number for a GM rep or Duramax. What causes this? Will it cause engine damage? How can it be corrected?
| Black Oil Caveman
Answer: Two different diesel engines decades apart in diesel technology can be an invalid comparison. Fundamentals tell us the majority of contaminants floating around in any engine's oil are from blow-by -- the exhaust gases that blow by the piston rings during the combustion stroke -- and it's unavoidable. Typically, when there is excessive blow-by, it's accompanied by higher than normal oil consumption. Don't know if they did, but the techs at the dealership can do both engine compression and leak-down tests to determine if you're getting a proper seal between the piston rings and cylinder walls. One thing you can do is monitor the amount of engine oil lost between oil changes. There should be a minimal amount lost in 3000 to 6000 miles. A rule of thumb I use: A quart burned between oil changes is too much -- you should not have to add oil before your next service.
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
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