First of all let me say I change my oil & filter every 5K miles in the 03 CTD. I use Fleetguard Stratspore filters an Delo 400 15w/40 Multigrade oil. I have noticed that at every 5K since new that the oil usage would be, if I were to guess maybe a pint, or so (guessing). I have never added an oil between changes, according to the owners manual it says to add when it gets to add mark around 2 quarts. Truck has always run fine, no excessive smoke, no abnormal sounds, etc. It will stay right on full mark when I first service it to about 3K miles then I start noticing a slight drop off the full mark until it reaches the 5K change. (I check the oil about once a week) I've talked to a good mechanic friend of mine about it an he will just kinda laugh, an say that's no oil usage to speak of, an I agree. It just bugs me that it will go 3K miles on full mark an then start slightly dropping off. Also when I check it I let it set over night an its always same location on the stick slightly under full mark, but above the full mark there may be a small section that is showing a drop or so of oil. Oil is always clean looking until around 4K an then has a slight color change to it (never have seen it black). I have 19K plus miles on it to date with no towing what so ever in the last year. I towed with it at first when truck was new (some towing with a travel trailer around 6K lbs), but not any in the last year at all. I had a very, very, small valve gasket oil leak fixed here recently, but you could not tell it was so small leak you barely would show any oil on a paper towel when I wiped it across. No excessive amount of oil around vent tube to speak of either. Never have done a oil analyze on any vehicle before, but plan to on the CTD at the 20K oil change. After all my rambling here my question would be where is that slight drop of oil on the oil stick going after you reach 3K to 5K. Why would it not just stay on the full mark the full 5K change interval. Looks like if it was going to use a pint of oil it would do it when I change each interval from the start. I've seen others say here on the TDR, their's would not use a drop between changes. Sorry for the long post, just curious more than anything why it would wait to after 3K to start showing a slight oil usage. 
