It's engine oil. I have an oil cooler, I had a friend looking under the reck for it, as I wasn't dressed to crawl under it and look. But I guess that's what I get for having someone else do it. My question is...the coolant itself is clean looking, but the walls of the degas bottle are caked with oil residue pretty heavily. Is there any chance of getting coolant back washed into the oil system? I did a test for fuel in the oil, and that checked out. My concern is long term damage caused by this issue, and any other possible issues. Headgaskets??? I don't hear much about headgaskets on 7.3's, but anything is possible I guess. Since it's got colder, it will smoke white out of the exhaust when cranking it, and for the first few minutes of it running. I just chocked that up to it being un-ignited fuel, but it makes me wonder if there's a bigger issue. It's due for an oil change, can oil cause that problem? I was making an attempt to sell it to a member here, but I can't with a clear conscience sell it to them with this issue, if it's bugger than a new cooler, and flushing the system. I'd like to make the deal work out, but if I've got to spend some money to make bigger underlying problems right, I'm not going to do it, as I wouldn't be able to sleep knowing I sold somebody something with an issue. This has been the most quirk/problem free vehicle I've owned. Hell, my Denali had to have a transmissionput in at 40k miles, and this one went 240k before I encountered a problem with it.