I just bought this 2005 lly and I was checking over the fluids and I decided to smell the oil, it smells like onions or maybe gear lube. Has anyone else experienced this? Someone mentioned it could have a quart of gear lube dumped in to make a knock possible go away. I changed the oil with mobil delvac 1300 super 15w-40 yesterday. I drove it 15 miles to work this morning, checked the oil and it still had the smell of what I smelled before. Drove great and sounded just as quite. I have been doing a lot of searching around on this topic and found a few possible answers. Somewhere on a Cummins forum someone noted that shell rotella had an odd sweet onion / gear lube smell. I have also read that zinc-phosphorous can smell like what was described, which I believe shell rotella has in it. ZDPP is also an oil additive that is basically zinc-phosphorous. Sulfer can also smell like this another user online stated. I'm hoping I am just paranoid at this point, I will have to see what happens with the new oil in it, the smell might stay for a few oil changes also who knows? When I got the truck the oil was probably in there for 5,000 miles or so (just based on the % ) and I drove it for another 1500 miles, so I'm thinking someone just didn't change the oil and dump some oil honey in it to make things less noisy, but who knows. It has never smoked odd, sounded odd or anything. I also got about 19 mpg on a 3 hr trip and have been averaging 17 mpg the entire time. I'll update this after some time. One question, how long does it take for your guys oil to turn black after an oil change? Thank you!!