MPG Steadily dropping….

[aevgladitorrubi]

20 in town is insane. I wonder if there was a calculation problem. I can't even get 20 on the highway in a stock Mojave.

diesel-- got 25.7 home from the cigar lounge last night, only 1/3 highway miles...

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[ZoMojave]

Gas engine? I’m running diesel. And yeah I’m noticing it dropping about 3 mpg lower than normal since I filled up last, so I’m thinking it must be the winter blend.

Yup. Pentastar.

 

[Teqsand]

What? Do you know what driving in town means? I guess not. Let me specify. City driving. Not on the highway. Not Interstate driving long distance. . “Town” driving, “City” driving, whatever you want to call it, is stop in go in traffic, etc. got it now? Is it clear enough?

Yup I get it, and I get 19/20 on 37' driving IN TOWN all day long... I get 22'ish NOT IN TOWN all day long also.... is that clear enough for you?

 

[Mike-len]

Most of you seem to have glossed over the OP's GFC, a permanently installed camper that sticks up above the cab for permanent extra air resistance and weight. Sorry to say (since rattling off your own personal MPG history seems to be a favorite pastime of this board) but anyone with an open bed is not very relevant here

I put a heavy Alu-Cab camper on my JTRD two months after getting the truck, 37s and a weighty lift 6 months after that, then a slowly increasing amount of gear and furnishings permanently installed in the camper. The weight adds up, and it really matters. You're welcome to browse my MPG history, which seems a lot more relevant to yours than most here:

https://www.fuelly.com/car/jeep/gladiator/2022/fourfa/1156647

Broadly similar to what you're reporting. Lately in pure city 17 isn't unusual, and the max I see on the freeway is 22-23. Overall combined 19-20. All taken from obsessively corrected odometer (calibrated by long GPS distance tracks, disconnected from the truck GPS)

As for the sudden drop, yeah most likely winter diesel. Track it over a few years and it'll probably show up every year.

I’ve had the GFC on for several months and it did not change my mpg at all. The GFC weighs 240 lbs. The diesel doesn’t even know it’s back there and performance was not affected at all. This happened within the past week when I noticed several miles less per gallon. I’m thinking like a lot of people have said is that it may be due to winter blend changeover.

 

[sharpsicle]

If I remember right, I thought I saw an article saying winter blend was authorized to be rolled out earlier than usual this year. The weekend of Sept 16/17 if memory serves. Usually it's not out until late October.

 

[Mike-len]

If I remember right, I thought I saw an article saying winder blend was authorized to be rolled out earlier than usual this year. The weekend of Sept 16/17 if memory serves. Usually it's not out until late October.

I think that is exactly what is going on. I don’t drive it in the winter because of the salt they use on the roads, so I’ve never noticed if there’s a drop in mpg or not.

 

[Chestnut]

No it’s definitely not the tires. I’ve had the tires on for at least 6 months. We took a trip out west to Montana, Idaho, and Wyoming, and I was averaging 22-24 (on the gauge) for the total trip of around 2500 miles even through the mountains. It definitely started around the time I had the oil changed, but I also remember filling up with diesel the day before. I think our area has already switched to winter blend diesel, so I think I may have figured it out after someone else here mentioned it.

I think they switched over to winter blend. I was getting 20-21 on my gas but after my last fill up driving the same roads to work and back I'm getting 18.5.

Last year this time we were what 40 degrees cooler and a week away from our first snow? 91 degrees on October 1st is crazy and way too warm.

 

[Mike-len]

35 psi seems high but that shouldn’t hurt MPGs. I chalk tested my 37s, albeit KM3s which is a different tire and I run around 27-28PSI.

With all my bullshit bolted on (rack, awning, bed full of overlanding junk) I can easily get 27 @ 70MPH and 30ish @ 65MPH. It get combined 22MPG but I drive like a bat outta hell. The torque of the diesel turns me into Mr. Wheeler doing 85 down the interstate.

Going to 37s, I saw a noticeable drop. But if you haven’t changed anything, I’d be concerned that something is wrong seeing dropping MPGs. It might be due for an ecu update/flash.

I’ve never seen above 26 ever, and once I go above 65 it starts dropping. On my trip through Montana, Wyoming, and Idaho this summer I average 22-23 the whole trip with all of my overlanding gear in the back and the go fast camper on as well. I was under the impression that higher tire pressure gets you better mpg. If I got above 35 psi on the 37” Ko2’s, the ride really gets rough but I noticed better mpg.

 

[Mike-len]

I think they switched over to winter blend. I was getting 20-21 on my gas but after my last fill up driving the same roads to work and back I'm getting 18.5.

Last year this time we were what 40 degrees cooler and a week away from our first snow? 91 degrees on October 1st is crazy and way too warm.

Agreed. 90 degrees yesterday in Minnesota and close to that today too. 30 degrees above average. I’ll take this I’ve frigid temperatures and snow any day though.

 

[@californiajeeping]

Agreed. 90 degrees yesterday in Minnesota and close to that today too. 30 degrees above average. I’ll take this I’ve frigid temperatures and snow any day though.

you need to get a banks IDASH and start monitoring your DPF soot load. The single largest MPG killer on these is that DPF soot load and regen. It can also monitor fuel and boost pressures.

I will say im in california but when my gladiator was stock on 38" tires. I rarely saw less that 19mpg. That was my worst fuel economy climbing the sierras into nevada. This is a 1500-6500 elevation climb over 1 hour.

The average with the stock diesel and 38" tires was around 22mpg climbing normal foothills of sea level to 1500ft. This was 75-80mph highway travel in the foothills.

If your getting 17mpg and not climbing a mountain....you have something going on. Either abnormally high SL reading causing frequent regens or possibly a restriction causing low boost pressure. Or possibly have bad fuel maybe even water in it. Your computer is reading X fuel injected over X distance. Something is causing that to be higher.

 

[Mike-len]

you need to get a banks IDASH and start monitoring your DPF soot load. The single largest MPG killer on these is that DPF soot load and regen. It can also monitor fuel and boost pressures.

I will say im in california but when my gladiator was stock on 38" tires. I rarely saw less that 19mpg. That was my worst fuel economy climbing the sierras into nevada. This is a 1500-6500 elevation climb over 1 hour.

The average with the stock diesel and 38" tires was around 22mpg climbing normal foothills of sea level to 1500ft. This was 75-80mph highway travel in the foothills.

If your getting 17mpg and not climbing a mountain....you have something going on. Either abnormally high SL reading causing frequent regens or possibly a restriction causing low boost pressure. Or possibly have bad fuel maybe even water in it. Your computer is reading X fuel injected over X distance. Something is causing that to be higher.

Good info. I’ve been planning on getting one. I run the Banks pedal monster now and love it. I’ve never seen any regen notifications and I just turned over 12,000 miles.

 

[@californiajeeping]

Good info. I’ve been planning on getting one. I run the Banks pedal monster now and love it. I’ve never seen any regen notifications and I just turned over 12,000 miles.

theres passive regen: you get the dpf hot enough driving to burn off it does run some extra fuel I believe to accomplish this and theres active which is where the idle is raised and it increases injection of fuel drastically to get the dpf hot. This is where you see people lighting paper on fire at idle near the exhaust outlet.

Passive regen happens in the background and active is the fuel killer with a warning on dash. But if your floating around 60-70% soot load and constantly triggering passive regen it can cause issues. One wrong reading from a sensor and this happens. At 60-70% soot load of the DPF your driving around with 30+ PSI of drive pressure at the turbo. That is massive.

 

[Mike-len]

theres passive regen: you get the dpf hot enough driving to burn off it does run some extra fuel I believe to accomplish this and theres active which is where the idle is raised and it increases injection of fuel drastically to get the dpf hot. This is where you see people lighting paper on fire at idle near the exhaust outlet.

Passive regen happens in the background and active is the fuel killer with a warning on dash. But if your floating around 60-70% soot load and constantly triggering passive regen it can cause issues. One wrong reading from a sensor and this happens. At 60-70% soot load of the DPF your driving around with 30+ PSI of drive pressure at the turbo. That is massive.

Very helpful. Thank you.

 

[Wolf Island Diver]

I’ve never seen above 26 ever, and once I go above 65 it starts dropping. On my trip through Montana, Wyoming, and Idaho this summer I average 22-23 the whole trip with all of my overlanding gear in the back and the go fast camper on as well. I was under the impression that higher tire pressure gets you better mpg. If I got above 35 psi on the 37” Ko2’s, the ride really gets rough but I noticed better mpg.

On the tires that’s what I said. Running those pressures shouldn’t be causing bad fuel economy only the those pressures seem high to me. Never getting above 26 seems strange. You’re telling me on the interstate on flats at 55-65 you can’t get above 26MPG? I agree that above 65 mileage begins to drop. But I can still hit mid 20s or a little higher between 65 and 70 on flats. Below 65 my mileage goes up. If I ran 55 all the time, I’d be getting high 20s - low 30s.

I’m not claiming getting 27-30 averages. I’m saying that on the interstate, apparently regardless of what I’m carrying, and on flat terrain, I consistently see 27MPG+ @ 65-70 MPH. Below 65, I easily see 27MPG. I can easily see 30+ below 60. Again this is interstate or byways. This is all using the onboard computer.

 

[Mike-len]

On the tires that’s what I said. Running those pressures shouldn’t be causing bad fuel economy only the those pressures seem high to me. Never getting above 26 seems strange. You’re telling me on the interstate on flats at 55-65 you can’t get above 26MPG? I agree that above 65 mileage begins to drop. But I can still hit mid 20s or a little higher between 65 and 70 on flats. Below 65 my mileage goes up. If I ran 55 all the time, I’d be getting high 20s - low 30s.

I’m not claiming getting 27-30 averages. I’m saying that on the interstate, apparently regardless of what I’m carrying, and on flat terrain, I consistently see 27MPG+ @ 65-70 MPH. Below 65, I easily see 27MPG. I can easily see 30+ below 60. Again this is interstate or byways. This is all using the onboard computer.

I did see 26mpg average on a trip we took recently where I drive around 60-65 the whole way. That’s the only time. Yes I do see some real time numbers of 24-25, but nothing like that since my last fill up. I’ll be taking a weekend trip a few hours away in a few days where I’ll be driving interstate for most of the drive and I’ll monitor on that trip and see how it looks. I’ll be replacing the fuel filter before that trip as well.

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