I don't know if this is odd or not; it is to me, but since I'm new to diesels, maybe it's pretty simple, and I just don't know it.
Recently bought a 2006 Lariat, 2X4, had about 115k miles, studded, Air Raid filter, EGR
delete, and 4" exhaust. For the first tank of diesel, I was getting just a shade under 16 MPG
, which I thought was a little low, but okay. After that first tank, I changed both fuel filters (Motorcraft replacements), and both the oil filter (Motorcraft again) and oil (Rotella T6), and started to use Arch Oil AR6200. The second tank saw mileage drop to 15, the third dropped to 14.2, and the most recent was all the way down to 13.5 MPG
. I don't have a scanner yet, but there's no unusual readings on the standard gauges; everything seems to be within normal, or at least expected, ranges. There isn't any real hesitation, sluggishness, smoke, or what sounds or feels like a skip; honestly, I don't even know where to start, I've never had this issue with my trucks before (although they were all gassers).
Any suggestions as to what to look for, or check...?