Back in the day Rotella is all I ever ran in my 440 and that's what I run in my diesels. I'll never use T6 5/40 synthetic.I was out of town and needed my oil changed bad and saw that they had a sell on the T6 so I bought it and changed my oil. By 4,000 miles it had already went through a little over 3 quarts and this truck only uses 1 quart every 5,000 miles. I changed quickly, drained it again and changed once more. I don't know where it went and don't care but when I freshen up my motor I think I will run 15/40 again.