I have done extensive record keeping about what improves the mileage on my N14 Cummins, as I am a long-haul truck driver. During the $4.50 plus days, I was going crazy trying everything to increase my mileage above 5.5 mpg. The only thing that consistently worked, was to use an upper cylinder lubricant in the correct amounts. I used a gallon of Lucas, or 1/2 gallon of 2-stroke oil for approximately 300 gals. They were the only products that consistently raised my fuel mileage and quieted the engine down. However, since 2-stroke oil doesn't have an injector cleaner, I had to put that in, either as a dedicated cleaner, or switch to the actual Lucas (or USA Lube) at least once every six fillups. ATF made no difference on my fuel mileage or quieting down the engine, but worked as an injector cleaner, in the right amounts. Unfortunately, the ultra low sulfur diesel does not perform as well on our older MBZ or heavy-duty truck engines, necessitating a regular dose of upper cylinder lubricant. However, I have noticed that Bio-diesel does quiet things down, if at least B11, but didn't make a difference in mileage, and maybe a bit less power.

I'd stick with 2-stroke oil or Lucas, and definitely use anti-gel in winter.

Torie