So after reading alot of posts regarding regens and how much fuel it potentially uses I decided to check it myself.

Let me start off by saying I'm getting around 15.9 to 16.3 mpg. I got 17.2 one time so there must have been more hwy driving that tank. This is hand calculated using my app on my ipod touch. I now have 11 entries in the app to get a good average. I'll base this on the last 3 entries which are as follows:
16.1 mpg
15.9 mpg
16.3 mpg

My regens kick in around every 500 miles or just past 1/2 tank. On trip A that's at around 260 miles (I reset trip A every fill up). I also fill all the way up to the neck to where I can see the fuel so it's consistent each fill up.

Since I know when the regens occur I decided this time I'd get fuel just before the regen to see what my fuel economy would be without a regen. To my surprise it's 16.7mpg. If I base that on the last fill which was 16.1mpg, that's only a difference of .6 mpg that I'm losing due to a regen. Right after I filled up my regen kicked in 24.2 miles later.

Just thought I'd share my little test.......

 

hlozano, thanks for posting. I cannot get that kind of mileage even in a good day. The 4.88 gears and little heavier truck make up my difference. I get about 12 mpg at best (without regen happening). I am not complaining, knew that going in when I bought this truck for towing. Have a great weekend my friend.

 

Every time I get a regen and it completes, I notice my miles to empty + trip meter reading since my last fillup drops by about 30-40miles. sigh... So that works out to be almost 3 gallons of fuel per regen

There seems to be 2 types of regens... one that lasts 15-20 minutes or so every few hundred miles, another that lasts for days every couple of thousand miles. That drinks diesel like me drinking beer.

 

Interesting info hlozano. Thanks for sharing.

 

58K on mine. Never experienced one of these that lasts for days. The 10-20 minute one at 100 -300 mile intervals is common for me.

If mine drank diesel like I drink beer, my fuel guage would never leave the full mark. :-)

 

Keep a close eye on it and the odometer and you'll notice that even though it dropped like that you'll go 2-3 miles for each mile on the "miles to empty" screen as it evens itself out. It freaked me out at first, but after starting with a full tank at 464 miles, doing a regen as soon as I left the station, and seeing it drop to 440 miles, I actually put 410 miles on the truck before getting gas again. When I did, it said I had another 167 miles to "E", and only took on 23 gallons of fuel. That left me with another 7 gallons in it still. Too lazy to do the math, but I average 17.5-18.5mpg somehow...In Colorado of all places. 99.9999% of it is highway miles though.

I think it uses a quart for the small regens, and maybe 2 for the big ones.

 

12K on my truck now. Most of my driving is 30-40mph stop-and-go. I'd guess my city/freeway mix is 70/30. I'll bet anything that's where my marathon regens come from. Irritating :-(

I've started experimenting with Diesel Kleen. Let's see if that really makes a difference like some claim. I'll see how it goes after the next few tanks of fuel.

 

I started using Diesel Kleen 4 tanks ago. Based on my gas calculations, I see no real change in regens or fuel economy. I may have picked up .3 mpg since I started using it or traffic was a little heavier prior to using it, either way, no real gains. I've also read alot of people claim the throttle is a little more responsive. Again, I feel no change in throttle response either. The only reason I'm continuing to use it to keep the injectors clean. So for the additional $1.75/tank I'll pay for the peace of mind that Diesel Kleen is prolonging my engine life. I'm sure it'll get to a point I'll get tired of the hassle of buying it and putting it in every fill up.

 

Read the back of the bottle...you can double up on it, and that is when it makes the bigger difference. 10oz instead of 5, for instance.

 

It's been 4yrs, 9mos since I posted the above comment. I thought it would be interesting to post my 6.4's regen behavior and mileage since my original post. I still use the same app to input my fill-ups and mileage and I still painfully wait for the fuel to fill-up to the neck. My regens faithfully kick off around 300 miles between regens and more often when I'm towing. I still get the dreaded white smoke for the first few minutes during regen. My fuel economy is about the same as what I originally posted.
15.73 mpg
16.16 mpg
15.06 mpg

I attribute the change in fuel economy to a lead weight in my right shoe...