I usually go 5000 miles between oil changes. I know my book says 7000 for light duty and 3500 for severe duty so I just split the difference. Recently though I installed RV injectors and a BD modified stock turbo. Well now my truck smokes quite a bit and now I'm on a road trip in Mexico burning the old fashioned low sulfur diesel that has doubled my mosquito killing capabilities. My question is with all this unburned fuel going out my tailpipe is my oil getting dirty quicker too? Thanks.