Sudden MPG drop- engine issue or winter diesel?

[GOLDGlad]

So, my '23 Gladiator Sport S has been awesome. Especially in terms of mileage, even after putting on 33" tires I was getting 27-25 MPG. I have no other mods. 14K miles in 7 mos.

In late October, my mileage started to drop like a rock. My average mileage has plummeted from 27-25 down to 20-21.

I live in Northern Illinois, and temps have been dropping as you'd expect, but I didn't think "winter diesel" was supposed to involve a 30% drop in fuel efficiency. What gives? The local jeep dealership techs are saying its just winter diesel, but it can't be that much of a difference, can it? I have noticed no other differences in performance. What's your opinion?

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[nanook12]

Are you letting it idle to warm it up? That skews the mileage… you have to figure it out by topping the tank.

 

[Towzone100]

Try Hot Shot's Secret Diesel Extreme.

 

[GOLDGlad]

Are you letting it idle to warm it up? That skews the mileage… you have to figure it out by topping the tank.

Not every time, depending on the temps. No one here trusts the computer's mpg calculations, I'm guessing.

 

[Rusty PW]

Mine doesn't like the colder temps. I noticed a drop in fuel mileage too. About 2 mpg.

 

[OldSarge]

Try Hot Shot's Secret Diesel Extreme.

I use Hot Shots in my F250 diesel, recommend this as well. May not improve mileage enough to justify the cost, but is good for your fuel pump and injectiors

 

[jywolfe]

I've been using HS EDT on every fill-up and recently ran a dose of Archoil AR6400-D. My fuel mileage on my 2023 Willys had a significant drop over the summer. I was easily able to get 29 highway and around 25 mixed (computer) on my routine 4 hour trip and some local commuting mixed in; and then something shifted this summer and it dropped precipitously to 22.8 mixed and barely 25 on highway. I thought maybe it was a bad tank of fuel, even though I fill up at the same stations consistently. Unfortunately it never fully recovered, and now I'm lifted and have bigger tires so I can't really return to my baseline. After running a full dose of AR6400-D I noticed a significant return of power and torque and fuel mileage crept up to 23.5 MPG mixed (before lift) after two tanks but not back to the fuel economy I had before. Interestingly my wife's Wrangler JL with the Ecodiesel gets 33 (computer display) average on the same 4 hour trip over 216 miles.

I will also note her's only has 4000 miles now and mine has 10,600. Also a very interesting distinction between our two vehicles is that hers has only regened twice and mine has 17 regens. Shortly thereafter I drove it on the same 216 mile trip and the passive regen brought it down to 49% soot load and it never did an active regen. My Gladiator only drops about 15% on that same trip.

I don't know the answer to why our two diesels are so different, but her Wrangler has more pep and power. It revs faster and has better throtle response. Both have had the fuel pump recall and we use the same fuel and I've run Hot Shots EDT in hers since the first fuel fill up at 600 miles and I started mine on EDT at 700 miles.

Also, both use the same oil change intervals, and oil filter, although I recently switched the Gladitor to the Ecoguard as an experiment. Up until last weekend I had run Mopar Oil filter in both. The only real difference is I use Castrol Euro oil in hers and I've used Pennzoil and Quaker State Euro in mine. I recently sent oil from the Gladiator in for analysis on my last oil change right at 10K and I'll do the same for hers at 10K. My OCI interval on the Gladiator has averaged 1500 miles, but now that I've just hit 10k on mine, I'll stretch it out to 4000. The same is true for the Wrangler, with an 1214 average OCI; I did an initial oil change at 702, 1932, and the last was at 3639.

My Gladiator is a little heavier, not exact but probably around 500 pounds due to topper, Decked system and tools. The Wrangler has no real additional weight other than passengers.
The Gladiator also has different aerodynamics, but I'm not sure if these two factors should be dragging my fuel mileage that much lower.

 

[Jefe1018]

I too suspect winter fuel.

What’s crazy to me is that my winters are much more mild than most and my summers also suck way worse. On 37’s and stock gears I’d get 15–16’s city from June through mid October and 17-19 city until it got warm again. I think this lotto diesel is very picky on ambient temps.

 

[jav_eee]

Not every time, depending on the temps. No one here trusts the computer's mpg calculations, I'm guessing.

hand calculate. Always.

 

[RoamingGladiator]

I always see a small drop in fuel efficiency from November to April with the winter fuel swap. Normally 23-25mpg during the winters on 37s.

 

[ZeeJay]

About normal in anything to suffer mileage during winter. Partly from idle time and partly from parasitic loss from cold fluids, e.g. transmission and differential. But that’s not the culprit, the root is emissions. Aftertreatment strategy is based off ambient air temp. The same temp you read on dash is also read by PCM for this strategy Engine is required to heat DOC up, it doesn’t heat itself up, DOC initiates all of it. Much harder to get DOC to 600-650 degrees in winter versus summer, also engine fights harder to develop that heat with inlet air temps lower vs summer into engine. This doesn’t include an actual regen in cold weather, that is actually more difficult for the engine to accomplish with cold temps. So the moral is engine ends up burning more fuel to save polar bears in the winter.

 

[Vtur]

Double check your tire size programming. It can effects both odometer and hand calculated result.

 

[GOLDGlad]

Double check your tire size programming. It can effects both odometer and hand calculated result.

My what?

 

[GOLDGlad]

I always see a small drop in fuel efficiency from November to April with the winter fuel swap. Normally 23-25mpg during the winters on 37s.

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.

 

[Vtur]

My what?

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

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