Declining diesel mileage

[grimmjeeper]

You are right about the wind variances. I knew I was driving in heavy wind when I got the 20mpg on the highway. I don't know about the regen and when to expect it to happen. Will I know when it does this and how often does it happen? I have about 7200 miles on my Jeep currently and haven't know if I've experienced one.

You probably have.

Lots of threads on using a gauge like ScanGauge or Banks iDash. That'll tell you when you're in a regen.

 

[STW]

34psi is closer what I'd use for 315/70R17 or 35s on road, and it's lower than I'd use for the stock Rubicon BFGs at 285/70R17 33s. And your diesel is heavier by a bit than my 2dr 2.0T Rubicon.

You mentioned your mpg dropped right after you lowered pressure. So that suggests causation. But then mpg continue to go lower, so that muddies causation. I understand your frustration.

Someone mentioned the ScanGauge and that seems to be a universal mod for the diesels but not other JLs. I ran one for 20 years in my (gas) TJ

 

[dcmdon]

Is it getting colder where you live.

The air is significantly "thicker" at 30 than it is at 70.

If you drive around town temp won't affect your mileage as much. But on the highway its a big deal. My gas Gladiator Mojave on XR wheels and tires gets 18 mpg in the summer and 14 mpg in the winter.

 

[JL Diesel]

I’ve had the random high ‘fan’ noise too on occasion in the beginning. Never figured out what it was and it’s hasn’t happened for awhile so kinda forgot about it.

I’m running 35s with all steel bumpers and side rails so I know I’m heavier than some rigs but I get ~25 mpg on long highway trips and only ~19 mpg if I around town with all the stoplights and hills.

 

[BDinTX]

Good point @STW
@Feb14bgirl you might do a chalk test. I have no idea what the ideal tire pressure is for stock tires.
Plenty of videos out there, here's one:

 

[calemasters]

The very best fuel economy I can get is 29 mpg (best case). My average fuel economy (city/highway) is 23 mpg. If you are concerned about fuel economy, keep the tire pressure at 37 psi.

 

[Feb14bgirl]

All good thoughts and ideas everyone. My husband wanted to do the GDE tune when we first got the Jeep for engine performance but is hesitant because of the price. Since it does improve mpg's I might split it with him. I should not be that concerned about this because I do love the Jeep but after driving a manual Mini Cooper for years and getting in the 30's, my pocket feels the difference.

 

[Ratbert]

Your Jeep is basically a poorly-designed brick from the perspective of aerodynamics. I don't have the math memorized, but every increase in MPH has a more significant detrimental impact on your mileage then the last. The difference in MPGs between going 70 and 80 is pretty damn significant. The next increase by 10mph is significantly worse, etc.

Lots of potential causes have already been mentioned, but I don't think that I've seen anything about the possibility of a clogged air filter.

 

[Feb14bgirl]

Yes, a brick. I will check my air filter. Shouldn't be clogged but it's an easy check. I will also increase my tire pressure and do a tire pressure check with chalk. Easy to check this also. The hardest and possible the only culprit will be my heavy foot. It's hard for me to sit and let people pass me. I feel like it's a contest of sorts. I really appreciate all the time you all have taken to indulge my concern. I didn't a Jeep for the mileage but I did buy the Diesel for that.

 

[mchastings]

Hi. I just love my 2022 Jeep diesel. That being said, my mileage seems to be declining. On the first trip home from the dealership (about 200 miles) I got 26.9 mpg. I had hoped for 30 (haha) but my husband was in disbelief that I got so good. When I got home I lowered the tire pressure from 38 to 34. The next tank I got 25.5 on the highway. Was averaging 22-23 in town. I got about 25 on the highway for the next tank also but the fourth full highway miles was 24ish. This last highway trip I got 22 on the way there and checked it on the way back and got 23.5. The def is in the 60% full range. I have done no modifications. My driving remains the same. I admit though I do like to be one of the fastest on the road. I guess I expected the mileage to get better over time or at least remain close to the same. NOT go down. Anyone else have this happen or can explain why this is happening and if there is anything I can do? I also a couple weeks ago had the fan come on at a weird time and stay on until I pulled over and shut the Jeep off. It did it one more time then hasn't done it since. I'm describing as a fan noise since I assume that is what it is and it is LOUD! I'm a new Jeep owner so I have no experience with them or diesels. My husband tends to think I hear unnecessary noises but I don't. He took my Jeep to work today and thinks it sounds the same. Help!

I had the same happen to me, but it was after I had about 6000 miles on it, it has stabilized at 24.5 mpg average and 19mpg avg. when I tow my trailer. I have over 50k on it now.

 

[JL Diesel]

It's hard for me to sit and let people pass me. I feel like it's a contest of sorts.

I’ve found it’s especially harder to play that game in my Wrangler vs my wife’s 4Runner. People seem to have a real issue being passed by a jacked up Wrangler haha.

 

[Feb14bgirl]

I had the same happen to me, but it was after I had about 6000 miles on it, it has stabilized at 24.5 mpg average and 19mpg avg. when I tow my trailer. I have over 50k on it now.

Pulling a trailer is why my husband pushed me towards the diesel. He only gets 12ish with his GMC. I don't think I'll tell him what you are getting or he'll want to take my Jeep more often.

 

[john adams]

Hi. I just love my 2022 Jeep diesel. That being said, my mileage seems to be declining. On the first trip home from the dealership (about 200 miles) I got 26.9 mpg. I had hoped for 30 (haha) but my husband was in disbelief that I got so good. When I got home I lowered the tire pressure from 38 to 34. The next tank I got 25.5 on the highway. Was averaging 22-23 in town. I got about 25 on the highway for the next tank also but the fourth full highway miles was 24ish. This last highway trip I got 22 on the way there and checked it on the way back and got 23.5. The def is in the 60% full range. I have done no modifications. My driving remains the same. I admit though I do like to be one of the fastest on the road. I guess I expected the mileage to get better over time or at least remain close to the same. NOT go down. Anyone else have this happen or can explain why this is happening and if there is anything I can do? I also a couple weeks ago had the fan come on at a weird time and stay on until I pulled over and shut the Jeep off. It did it one more time then hasn't done it since. I'm describing as a fan noise since I assume that is what it is and it is LOUD! I'm a new Jeep owner so I have no experience with them or diesels. My husband tends to think I hear unnecessary noises but I don't. He took my Jeep to work today and thinks it sounds the same. Help!

My MPG are down 2 MPg (26 to 24 on Rubicon) with the onset of cold weather.

 

[Feb14bgirl]

My MPG are down 2 MPg (26 to 24 on Rubicon) with the onset of cold weather.

I'd happily take/accept a decline for cold weather. Cold weather rarely happens in the Houston area.

 

[john adams]

I'd happily take/accept a decline for cold weather. Cold weather rarely happens in the Houston area.

I am not complaining. I have zero interest in the heat available south of about Maryland except during winter vacations.

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