Highway driving gears/transmission/speed

mgarciaknight

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I just got my 2021 JLU80 with the 3.6 etorque and auto 8 speed tranny (600miles). I do quite a bit of highway driving. I was cruising, using cruise control, at 80mph on a FL highway (flat) realized I was in 7th gear and I wondered why I wasnt in 8th gear since its an 8 speed transmission. I started going down slowly 1 mph until I saw any type of change. Not until I came down to 76 mph did it shift up to 8th gear. I went up to 77 and it came back down to 7th gear. I always thought one of the points of having more speeds was to better the highway mileage, as in an overdrive. I know our Jeeps are heavy and require a lot of energy to push them along, but to lose one entire speed seems counterproductive. Thoughts?





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5foot19

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What was the wind like? Wind resistance isn't linear, if you increase your speed by something like 10mph you double the wind resistance ( and the amount of force to push your jeep through the air). It's the only thing I can think of
 

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The 3.6 needs high rpm to maintain speed. With your stock gearing, 8th is a downhill/cruising gear. 7th is an overdrive gear as well.
 
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mgarciaknight

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What was the wind like? Wind resistance isn't linear, if you increase your speed by something like 10mph you double the wind resistance ( and the amount of force to push your jeep through the air). It's the only thing I can think of
Definitely zero wind that day, of course other than the wind resistance of pushing a barn door at 80 mph.
 

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I just got my 2021 JLU80 with the 3.6 etorque and auto 8 speed tranny (600miles). I do quite a bit of highway driving. I was cruising, using cruise control, at 80mph on a FL highway (flat) realized I was in 7th gear and I wondered why I wasnt in 8th gear since its an 8 speed transmission. I started going down slowly 1 mph until I saw any type of change. Not until I came down to 76 mph did it shift up to 8th gear. I went up to 77 and it came back down to 7th gear. I always thought one of the points of having more speeds was to better the highway mileage, as in an overdrive. I know our Jeeps are heavy and require a lot of energy to push them along, but to lose one entire speed seems counterproductive. Thoughts?

Your powertrain is more efficient in 7th gear at 80 mph. At 70 mph you are parting less air so the powertrain can handle 8th gear. The 3.0 L diesel can handle 8th gear at 80 mph due to its higher torque output.
 

Hound Dog

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More power is needed to push that cinderblock on wheels through the air. It needs to downshift to get that power.

Now if the jeep had the smooth aerodynamics of a cow, you could slip right through in 8th gear.

12597.jpeg.jpg
 

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I’m curious, do you guys have an indicator that tells you you’re in 7th instead of 8th? Or do you just know it?
My Jeep’s manual.
 

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Definitely zero wind that day, of course other than the wind resistance of pushing a barn door at 80 mph.
wait till you get to drive in some fun 40mph coming at you 10-2 stuff, I had that yesterday during first part of a 400 mile drive. It bumped my gas milage down about 3mpg in a manual.

So yeah, your auto tranny sensed that it needed 7th based on the road, engine speed and your foot or computers foot.
 

sf5211

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wait till you get to drive in some fun 40mph coming at you 10-2 stuff, I had that yesterday during first part of a 400 mile drive. It bumped my gas milage down about 3mpg in a manual.

So yeah, your auto tranny sensed that it needed 7th based on the road, engine speed and your foot or computers foot.
I know what you mean Neil. Last year my wife and I were on the way back to NY from Connecticut. It was super windy and blowing straight at us. My Jeep (manual too) had to be downshifted as low as 3rd a couple of times. I started to think something was wrong with it. Nope just a strong wind. Never happened again.
 

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I know what you mean Neil. Last year my wife and I were on the way back to NY from Connecticut. It was super windy and blowing straight at us. My Jeep (manual too) had to be downshifted as low as 3rd a couple of times. I started to think something was wrong with it. Nope just a strong wind. Never happened again.
I did get to actually use 6th with that tailwind on the way back. got close to 23mpg.

Fighting wind is part of it. Ive pulled my share of trailers all over the place. Just part of owning a jeep, slow it down, stay away from all the nervous crap drivers and take it easy.

I was very thankful for my ambers yesterday morning.
 
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mgarciaknight

mgarciaknight

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I’m curious, do you guys have an indicator that tells you you’re in 7th instead of 8th? Or do you just know it?
My Jeep’s manual.
Yes, on the auto 8 speed, bottom right of D shows what gear you are in. That is on the center info cluster.
 

zeebo56

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Yes, on the auto 8 speed, bottom right of D shows what gear you are in. That is on the center info cluster.
you have to enable it in the setting.


supposedly around the 5 min mark.

Also on 35s I mainly see 8th gear if I cruise at 65. any faster and I am in 7th. Jeep JLU sport
 

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