Suffer poor MPG???

[MichaelT333]

Do you suffer poor MPG on the highway vs city?

It may be this: I get better MPG in the city than on the highway and my highway speeds are 64-74 cruise control. Need wondering why city gives me 14s-15s, Hwy drops to the 13s.

Then by accident and I often drive with my hand on the gear shift I move it into Manual on my Automatic and I look at the dash and I am in 6th GEAR and I am at cruise at 72 mph. I am on a trip of about 100 mi in interstate. I discover that I can only go into 7th/8th gear manually, it does not up shift to it.

NOTE: I been playing with this for a week and no matter I have to use manual to get into 7-8 gears.


Anyone else discover this?

Wow how is that so little mpg. I have a 2022 2door manual transmission and 34in tires, stock gears. I drive mostly highway at 75-85 and I never use cruise control. Right now I am sitting at 21mpg. I’m usually around 23

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[PBosch]

That isn't the best MPG. One question, did you buy a Wrangler, because I'm thinking that may be the cause.

 

[roaniecowpony]

Thanks to all that replied, I appreciate your comments.

That said My JLR has 35 x 12:50 x 17 GY Duratrac shoes. Outside of that it all OEM, 3.6.

It not so much a question of MPG, but rather WHY does it not shift into 7 & 8 gear even at speeds of 75 mph on a flat road. Instead I need shift into 7 & 8 manually. This seems to be a new thing with it. The 35 shoes have been on it since about new. and I am now at 2990 mi as of today. I only noticed this a few days ago going down I 75 and my engine screaming, looking at the RPMs and WTH, I shifted into M and it displayed 6, then I manually went to 7 & 8. And for the past week driving I 75 that the only way get to 7 & 8???

I assure you mpg has little or no meaning in my world.

The real question is: Why is my transmission not shifting to gears 7 & 8, has anyone experienced this?

Don, I would think the low hanging fruit would be to climb under and check all the wheel speed sensor harnesses, and any harness leading to the PCM and trans, and read the codes. After that, I'd have to dig into my manual.

 

[UniqueUserName]

If memory serves, weight will indeed cut down your mileage. if you take the same weight/width tire but different diameter, you tune and fix the speedometer and nothing changes. Change the weight and/or width and then its a different ball game. Higher weight makes it work harder to turn. I want to say for each lb of unsprung mass its like 7lbs of static weight. The width just causes more friction which will also increase mileage. Granted, this is what I recall and I could be wrong LOL

Larger diameter/same weight changes the gearing. You would have to change the gears to achieve the same overall gearing. Then there's increased drag effect at higher speeds too.

 

[Byrds8]

Larger diameter/same weight changes the gearing. You would have to change the gears to achieve the same overall gearing. Then there's increased drag effect at higher speeds too.

I stand corrected. I didnt think about it changing the overall gearing ratio. So I guess everything plays a part; diameter, width and weight.

 

[Ratbert]

Thanks to all that replied, I appreciate your comments.

That said My JLR has 35 x 12:50 x 17 GY Duratrac shoes. Outside of that it all OEM, 3.6.

It not so much a question of MPG, but rather WHY does it not shift into 7 & 8 gear even at speeds of 75 mph on a flat road. Instead I need shift into 7 & 8 manually. This seems to be a new thing with it. The 35 shoes have been on it since about new. and I am now at 2990 mi as of today. I only noticed this a few days ago going down I 75 and my engine screaming, looking at the RPMs and WTH, I shifted into M and it displayed 6, then I manually went to 7 & 8. And for the past week driving I 75 that the only way get to 7 & 8???

I assure you mpg has little or no meaning in my world.

The real question is: Why is my transmission not shifting to gears 7 & 8, has anyone experienced this?

Did you adjust the computer so it knows about the 35s?

 

[oldcjguy]

Thanks to all that replied, I appreciate your comments.

That said My JLR has 35 x 12:50 x 17 GY Duratrac shoes. Outside of that it all OEM, 3.6.

It not so much a question of MPG, but rather WHY does it not shift into 7 & 8 gear even at speeds of 75 mph on a flat road. Instead I need shift into 7 & 8 manually. This seems to be a new thing with it. The 35 shoes have been on it since about new. and I am now at 2990 mi as of today. I only noticed this a few days ago going down I 75 and my engine screaming, looking at the RPMs and WTH, I shifted into M and it displayed 6, then I manually went to 7 & 8. And for the past week driving I 75 that the only way get to 7 & 8???

I assure you mpg has little or no meaning in my world.

The real question is: Why is my transmission not shifting to gears 7 & 8, has anyone experienced this?

You can change a setting in your cluster so it shows you what gear you're in at all times. Instead of just "D" it would read "D6" when you're in 6th gear. Etc... It's in the settings of your dash cluster somewhere.
Check your exhaust. Did it get bent/pinched on an outing? Do you have some kind of obd2 monitor? Monitor your load and cat temps. See if something is going on there? Not sure what cruising load% should be on a 3.6

 

[roaniecowpony]

Thanks to all that replied, I appreciate your comments.

That said My JLR has 35 x 12:50 x 17 GY Duratrac shoes. Outside of that it all OEM, 3.6.

It not so much a question of MPG, but rather WHY does it not shift into 7 & 8 gear even at speeds of 75 mph on a flat road. Instead I need shift into 7 & 8 manually. This seems to be a new thing with it. The 35 shoes have been on it since about new. and I am now at 2990 mi as of today. I only noticed this a few days ago going down I 75 and my engine screaming, looking at the RPMs and WTH, I shifted into M and it displayed 6, then I manually went to 7 & 8. And for the past week driving I 75 that the only way get to 7 & 8???

I assure you mpg has little or no meaning in my world.

The real question is: Why is my transmission not shifting to gears 7 & 8, has anyone experienced this?

Don,
Here's the first page out of the manual and a couple more for transmission diagnosis. This is about all I could find in the mopar manual that is external diagnostics.

 

[azjl#3]

Depends on how fast you want to accelerate them. Jack your rear axle, put it in gear with big heavy tires on it. They'll spin up very quickly with little throttle. The only objective way to test weight alone is to use the very same tires with added weight. The effects of a larger diameter act against your drivetrain in the same way a longer lever arm works to generate more torque/force than a shorter one. Weight matters most when accelerating the tire, but even that is a low order effect as compared to other factors like diameter and rolling resistance created from wider tread, and especially more aggressive tread pattern. Then throw in that everyone wants to run lower tire pressures. Weight falls way down the list, especially at level ground constant speed cruise. But I'll give you it is there.

As an engineer, I disagree completely, sorry.

We are talking accelerating and decelerating here. Steady state, a heavier tire does not really add power needs, but it is more when you consider drag etc.

Weight matters most, not diameter, not footprint, not air pressure when truly accelerating, not just trying to go over a rock at slow speed, whole different issue there. The energy to accelerate a heavy tire is a square of the angular velocity. In other words, it's not 1 for 1.

Example, a tire weighing 5lbs, takes 25ft/lb power to rotate. A tire weighing 10 lbs takes 100 ft/lb to rotate. A factor of times more power needed, it's exponential.

You can see this work in real life when you air up those 100lb 35's to 40 psi and still get horrible gas mileage, and horrible braking. Looking at 4 tires, 400lbs , you need 300ft lb more power to rotate vs the lighter tire. This is of course an example, the power needed is just an example, but the math is true.

 

[Deleted User 38384]

I don't know man, that one time that I was super light on the pedal, and kept it at a max of 55 on the highways, didn't gas it hard from stop signs, I ended up with 33.45 MPG. But my average is about 23 mpg. I also have a very heavy foot too. Not all the time, but a lot of the time! Like when the traffic opens up on the highway, I'm not normally one not to gun it.

I don't know about the 3.6 l, but as for the EcoDiesel, the sweet spots seems to be right around 55 mph. I probably say if you slowed it down on the highways, kept it around 60 or so, and didn't hit the gas too hard from the stop lights and stop signs, you probably get a lot better MPGs

 

[roaniecowpony]

As an engineer, I disagree completely, sorry.

We are talking accelerating and decelerating here. Steady state, a heavier tire does not really add power needs, but it is more when you consider drag etc.

Weight matters most, not diameter, not footprint, not air pressure when truly accelerating, not just trying to go over a rock at slow speed, whole different issue there. The energy to accelerate a heavy tire is a square of the angular velocity. In other words, it's not 1 for 1.

Example, a tire weighing 5lbs, takes 25ft/lb power to rotate. A tire weighing 10 lbs takes 100 ft/lb to rotate. A factor of times more power needed, it's exponential.

You can see this work in real life when you air up those 100lb 35's to 40 psi and still get horrible gas mileage, and horrible braking. Looking at 4 tires, 400lbs , you need 300ft lb more power to rotate vs the lighter tire. This is of course an example, the power needed is just an example, but the math is true.

I would agree, if the tire/wheel acceleration and rotation is assessed in isolation. When you look at the combined vehicle weight, aero, frictional losses, tire rolling resistance, and all driving conditions, the acceleration of the tire/wheel is small. But the lever arm of the tire still works to exacerbate all of those variables, while the tire/wheel weight acceleration requirements remain constant.

 

[Blacktip]

Doesn't a Honda Element have a significantly smaller cross-section along with significantly smaller tires (less rolling resistance)? Cross section is a multiplier in the formula for aerodynamic drag, but at least it's not like velocity that gets squared.

Yes, you are right. The Element is smaller and lighter vehicle, but it has 4 cylinder with just 160 lb-ft. Even with a kayak on top, I was getting better mileage.

 

[Old Jeeper]

Don,
Here's the first page out of the manual and a couple more for transmission diagnosis. This is about all I could find in the mopar manual that is external diagnostics.

Thanks, actually was only wondering if any had experienced this. My 2024 JLR-X is going into production and I am just going to let this ride and the dealer can sort out when I trade it in. I don't drive I 75 often so not a big deal...

 

[Old Jeeper]

You can change a setting in your cluster so it shows you what gear you're in at all times. Instead of just "D" it would read "D6" when you're in 6th gear. Etc... It's in the settings of your dash cluster somewhere.
Check your exhaust. Did it get bent/pinched on an outing? Do you have some kind of obd2 monitor? Monitor your load and cat temps. See if something is going on there? Not sure what cruising load% should be on a 3.6

No off road and less than 3k miles since last Oct. I just noticed it due to sound in the cab about a week ago and did not think about to much. But I had to drive down south to Naples FL and about 200 mi rd trip and that is where I really discovered it...at 75 mph, loud engine and high rpm and it was in 6th. I was not driving it hard or pushing it, just on Cruise control. I will be trading it soon when my 2024 JLR-X gets built and let the dealer sort out.

 

[Old Jeeper]

Did you adjust the computer so it knows about the 35s?

They said they did it when I put them on which was back around Dec. Just noticed the engine nose this past week., not even 3k mi since Oct. I don't it often. So will live it since most drives are at city speeds and let the dealer sort out when I trade in for my 2024 JKR-X that should be on the way in early Aug.

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