Hello, I recently bought a 1990 Ford F-350 7.3 diesel to haul hay with in the winter time. It has 162,000 miles on it. We gave it an oil change, and put rotella T oil with a Fram oil filter in it ( I know, not the best oil filter) We drove it for about 1 hour, and the next day, checked it, and it was black again ( Not as black as the oil we changed from it, but not the "new oil" color) I have never owned a diesel (truck) before, and I was wondering if it is usual for diesels to do that. Keep in mind that the engine looks great(really dont matter how it looks) and more importantly runs great. ( for a 20 year old diesel, it cold starts GREAT) Thanks for replies in advance.