Sudden MPG drop- engine issue or winter diesel?

[Vtur]

I'm ok with a drop, but from 26mpg to 20??

I'm going to add the diesel additive as suggested, but I also realize that I have not noticed a single regeneration. If its happened, I've never seen it displayed on my dash, and I do a decent amount of highway driving.

Passive and active regens doesn't display on the dash. You need a device like an idash or Scangauge.

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[GOLDGlad]

Did you reprogrammed tire size when you went to 33s?

Reprogram what and how? haha. No, I've been on 33's since august, and my mileage plummeted in November.

 

[Vtur]

Reprogram what and how? haha. No, I've been on 33's since august, and my mileage plummeted in November.

Looks into Jscan, Alfaobd or a Tazer to tell the computer that it has bigger tires installed. The computer thinks that you're traveling a shorter distance due to circumference different, bigger diameter tires takes more distance to make one revolution. Since the speed sensor pickups are at the wheel hubs, it has no ways of knowing the different tires installed.

 

[Stan H]

What he is talking about is same for gas and diesel , if you have changed the tires from stock size then you must recalibrate the speedometer in the computer using a tazer or flashcal or banks programmer( very few dealers will do it for you now) . This will soft reset your trucks transmission shift points causing a passive relearn which will take approximately 1700-3000 miles for shift points to be relearn. A Jay scan can do a hard reset in the TCM module and make it learn immediately as if rolling off the showroom floor . Nevertheless. Once the new tire size has been programmed into the PCM the spedometer will start reading correctly. Dude before I did mine I dropped to 13.0 now I regularly get 17 after resetting size size and it relearning shift points. They are right Size Matters.

 

[RoamingGladiator]

I'm ok with a drop, but from 26mpg to 20??

I'm going to add the diesel additive as suggested, but I also realize that I have not noticed a single regeneration. If its happened, I've never seen it displayed on my dash, and I do a decent amount of highway driving.

I run EDT performance 2oz every single tank, I dont worry about winter additives since I live in Canada. Regens are not displayed on the dash as far as I'm aware. Most of us run Bullydogs or Scangauges to give better informaton, you really should get one if you do not.

 

[BuckeyeButch]

Yesterday I made a 600-mile road trip that I've done many times. Normally I would get 30-31 MPG mostly summertime trips. Yesterday I got 27.0 temps where in the mid twenty's. Bone stock Overland.

 

[Dougstdig]

Since 1991 or so, I always see a drop in performance including mileage in the winter months with winterized fuel. It’s a thing. This has been in semi’s all the way down to a 1.9L vw diesel.

Make sure you’re airing your tires back up when the temp drops. I see a fluctuation of as much as 5psi. This is of course a cold temp…or after the vehicle sits over night.

 

[rharr]

I have no idea how you guys are hitting high 20's and low 30's in MPG.
I am still on stock ruby tires with a 3" lift and am hitting 18-21 all the time no matter what, up hill down hill, pulling a light trailer....

 

[Riverdog]

I can't speak to the JT diesel specifically but yes cold weather does hurt mpg with any diesel I ever owned. We have the "winter" diesel here which helps it from freezing but also hurts mpg. I had a chevy cruz diesel that was getting 34 mpg in NY one winter. I drove it to Florida and between the warmer weather, better diesel and flat roads I was getting 56 mpg.

 

[Rusty PW]

I have no idea how you guys are hitting high 20's and low 30's in MPG.
I am still on stock ruby tires with a 3" lift and am hitting 18-21 all the time no matter what, up hill down hill, pulling a light trailer....

Same here. Some of the numbers posted seem high.

 

[rharr]

Same here. Some of the numbers posted seem high.

only time i got high 20's is when i filled up with some fancy hi centane bio fuel in CA. Some sort of R95 hi centane from Phillips/76.

 

[Rusty PW]

only time i got high 20's is when i filled up with some fancy hi centane bio fuel in CA. Some sort of R95 hi centane from Phillips/76.

Before I put the lift and 37’s on. Around town was 24 or so. Highway was 27 to 29 depending on speed limit. Now it's 20 around town. 24 Highway. Right now I'm getting 19 back and forth to work.

 

[Dougstdig]

Higher mileage also has a direct result with road elevation changes and actually the wind or the direction the wind is blowing or even a breeze. Sounds stupid, but it’s very true.

I can also run about 50 yards behind a semi be safe from any rocks and set my cruise to match his speed at about 71 72 and I’ll get 32-35 miles an hour. If I’m driving a farm to market Road here in Florida I can average in the low 30s as well, but if it was in Texas, where the FM roads are 75 miles an hour there’s no way I could do it.

As soon as you slow down and do some around town, driving or idling of any nature, the average goes through the floor.

 

[BuckeyeButch]

Just did a road trip from TN to OH & MI back to TN in bone stock Overland, speeds where 71-79 mph 95% highway with maybe 1/2 hr. of idling time what seemed like 80% head wind or very close to it temps in the 20's range. I always run in manual shift mode.

2,071.8 mile
27.8 mpg
36.52 hrs. running time = avg. 56.71 mph

 

[Dougstdig]

Just did a road trip from TN to OH & MI back to TN in bone stock Overland, speeds where 71-79 mph 95% highway with maybe 1/2 hr. of idling time what seemed like 80% head wind or very close to it temps in the 20's range. I always run in manual shift mode.

2,071.8 mile
27.8 mpg
36.52 hrs. running time = avg. 56.71 mph

Why do you always run in manual mode? Just preference?

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