I have a new 2016 Dodge Ram 2500 with the Cummins and already with only 1200klms on it the exhaust is black with soot. What's everybody's thoughts on this? I thought with the Adblu they are to run clean. A friend has one and a couple of others I've seen with more klms on it and they're exhaust is as clean as the day they bought it. I've just had it back at the dealer and they said this is normal for this engine and everything was working properly.