Chevy 3500 Duramax getting 583 MPG


Staff member
I've kept track the last 7,000 miles and the Duramax is getting 583 MPG DEF. From what I've read, this is lower than what most folks get with the L5P, but ours is almost always pulling the trailer and never used as a daily driver. DEF consumption is a function of fuel used.
OK - I have to admit I was hooked by the title ...
LOL - I don't like click-bait, but I couldn't resist.

It seems that 550-650 MPG/DEF is normal for the L5P when towing and 90% of miles on the truck are towing.
I assume you're still running the catalyst fuel additive, right? Is DEF directly or indirectly related to regen cycles? What triggers the DEF useage? Is it a function of the change in DPF % remaining, or something else?
Yes, still running the iron based catalyst and it seems to double to triple the miles between a regen, which is a very good thing. I have no way to measure if there is less soot in the EGR system, but logic would say there is less.

DEF has zero to do with the particulate filter regen. The regen uses fuel to heat the DPF to ignite the soot and turn it to ash, which mostly exits with the exhaust.

The diesel exhaust fluid, which is water and urea, is injected before the SCR catalyst, to react with NOx to produce N and O2. The consumption of DEF is supposed to be directly related to how much fuel you use. From what I've seen that is true.

This is widely misunderstood, even on the diesel boards. The DEF has nothing to do with a DPF regen.
Thanks Wayne. My older Dmax didn't have such equipment, and neither does my Kubota, so I'm not as much up to speed on those technologies as I should be.