Windows Open VS Air

FlaJeepDiver · **Posted:** Tue Sep 27, 2005 3:37 pm

You must have a magical Jeep, or you drive down hill all the time.
If you are getting 24mpg, please let us know I would love to get that kind of milage.

This is info directly from Chryslers press release.
EPA Fuel Economy (mpg City/Hwy) 19 mpg/23 mpg and that is for the
2.4 litre engine.

For the 3.7 it gets worse.
EPA Fuel Economy (mpg City/Hwy)
Automatic 16 mpg/20 mpg
Manual 16 mpg/21 mpg :cry:

Or you can read the specs at:
http://wwwsg.daimlerchrysler.com/SD7DEV ... 96,00.html?

Tightwadsjeeper wrote:

It's simply a matter of speed.
At lower speeds (below 50 mph) the increase in HP from the air being turned off outweighs the additional drag from the windows being down. Above the ~50 mph mark, the drag from the windows being open outweighs the power loss of the Air Conditioning being turned on.
Just got back from a weekend trip out of town... about 3/4 highway mileage this weekend with the majority of that being on the Interstate cruising with the windows up and the air turned on at the whopping speed of right around 63 mph... results:
388.1 miles on 18.01 gallons (tank filled to the top of the filler each time) = 21.5 mpg. Not Bad... especially for a 3.7L gas engine carrying the family and a fair load of gear aboard.
Luis

Turns out I was somewhat mistaken... the difference DOES weigh in favor of windows down and AC off until the speeds become much higher (~80+?) and the drag of the windows being down surpasses the HP loss of the engine to the compressor.

My last highway trip was 318.3 miles using 13.244 gallons of gas doing 60 mph with the windows down and resulted in 24 MPG.

Luis[/b]

Tightwadsjeeper · **Posted:** Tue Sep 27, 2005 4:14 pm

FlaJeepDiver wrote:

You must have a magical Jeep, or you drive down hill all the time.
If you are getting 24mpg, please let us know I would love to get that kind of milage.

This is info directly from Chryslers press release.
EPA Fuel Economy (mpg City/Hwy) 19 mpg/23 mpg and that is for the
2.4 litre engine.

For the 3.7 it gets worse.
EPA Fuel Economy (mpg City/Hwy)
Automatic 16 mpg/20 mpg
Manual 16 mpg/21 mpg :cry:

Or you can read the specs at:
http://wwwsg.daimlerchrysler.com/SD7DEV ... 96,00.html?

Tightwadsjeeper wrote:

Turns out I was somewhat mistaken... the difference DOES weigh in favor of windows down and AC off until the speeds become much higher (~80+?) and the drag of the windows being down surpasses the HP loss of the engine to the compressor.

My last highway trip was 318.3 miles using 13.244 gallons of gas doing 60 mph with the windows down and resulted in 24 MPG.

Luis[/b]

Nothing magical about it. I've gotten as low as 17.25 mpg on a tank where I hauled the boat to the ramp and back, and then had a touch of leadfoot for a small part of the rest of the tank. That 24 mpg trip was MOSTLY highway driving with the Liberty TOTALLY stock and the tires @ 35 psi, using the cruise at 60 mph with most of the mileage on the interstate totally uninterrupted. I'm pretty sure that the sticker on my '05 said 17/21 mpg not 16/20.

Don't forget that for them to post 21 as the highway rating, that it has to get much better than that during optimal cruising. I still remain convinced that running with the windows down and the air turned off helps substantially.... maybe the sunroof being open helps reduce the drag from the windows? I don't know. But I fill up very carefully every time making sure that I fill the tank all the way, so I'm sure that the gas mileage is correct.... unless my odometer is working incorrectly. Oh yeah... I typically take off more like a tortoise, than a jackrabbit... that REALLY helps.

Try this for your next tank....
1) Make sure your tires are FULLY inflated to 35psi or better
2) Run with the windows down and the AC off (no fan either... some of the settings engage the AC even when you don't have the button pushed in) as often as you can stand
3) Accelerate VERY slowly (pretend there's a raw egg between your foot and the accelerator)
4) Don't exceed 60 mph
5) Maintain a steady speed as much as possible (this means if traffic is running ~60 mph only go 55 so you never have to stop or slow down, and USE THE CRUISE CONTROL)
6) Avoid driving in the middle of the day if you can since the air is much hotter and has less oxygen in it (it actually makes your engine perform more poorly).

Force yourself to adopt these habits as often as you can stand, and if you don't already do this stuff, I virtually guarantee your mileage will increase a couple mpg (maybe more) on average. Of course, if you're lifted 6" and are running 35" tires, there's no help for you... LOL Even a 2" lift and 31" tires pretty much guarantees you aren't likely to exceed ~21 mpg tops.

BTW, my AVERAGE tank of gas gets me between 18.5 and 19.5 mpg.

Luis

Guest · **Posted:** Tue Sep 27, 2005 7:31 pm

Looks like wonderful advise, unless your did'nt notice my name. FlaJeepDiver. I live in South Florida were it is famous for Heat and Humidity. Today we had 91 with a feels like of 96. It's a bear to turn off the A/C and it sounds like hell if the windows are open when the 18 wheelers are along side. It's also dangerous since I go through about 15 miles of new road construction with flying rocks.
Highway speed is posted at 65-70 depending which section of the turnpike you are on. I run with cruise control when ever possible.
Do to heavy rains durning hurricane season I use 245/70 R16 tires with good tread properly inflated to a healthy 36psi.
Don't carry unecessary weight in the Jeep and average about 19 Miles to the gallon.
Got to get on the highway at a safe speed, that egg thing will get me rear ended by a semi for sure.
Oh and Florida is Flat as a pancake so hills are not a problem unless you count over passes.
I've put in the K&N filter, tune up with quality plugs, and change the oil religously. I wax when ever possible to reduce friction and it helps the mud slide off.

I was thinking maybe putting a sail on the roof? :wink:

But it is a Jeep and it does have to go off road for exersise.

Tightwadsjeeper wrote:

FlaJeepDiver wrote:

You must have a magical Jeep, or you drive down hill all the time.
If you are getting 24mpg, please let us know I would love to get that kind of milage.

This is info directly from Chryslers press release.
EPA Fuel Economy (mpg City/Hwy) 19 mpg/23 mpg and that is for the
2.4 litre engine.

For the 3.7 it gets worse.
EPA Fuel Economy (mpg City/Hwy)
Automatic 16 mpg/20 mpg
Manual 16 mpg/21 mpg :cry:

Or you can read the specs at:
http://wwwsg.daimlerchrysler.com/SD7DEV ... 96,00.html?

Tightwadsjeeper wrote:

Turns out I was somewhat mistaken... the difference DOES weigh in favor of windows down and AC off until the speeds become much higher (~80+?) and the drag of the windows being down surpasses the HP loss of the engine to the compressor.

My last highway trip was 318.3 miles using 13.244 gallons of gas doing 60 mph with the windows down and resulted in 24 MPG.

Luis[/b]

Nothing magical about it. I've gotten as low as 17.25 mpg on a tank where I hauled the boat to the ramp and back, and then had a touch of leadfoot for a small part of the rest of the tank. That 24 mpg trip was MOSTLY highway driving with the Liberty TOTALLY stock and the tires @ 35 psi, using the cruise at 60 mph with most of the mileage on the interstate totally uninterrupted. I'm pretty sure that the sticker on my '05 said 17/21 mpg not 16/20.

Don't forget that for them to post 21 as the highway rating, that it has to get much better than that during optimal cruising. I still remain convinced that running with the windows down and the air turned off helps substantially.... maybe the sunroof being open helps reduce the drag from the windows? I don't know. But I fill up very carefully every time making sure that I fill the tank all the way, so I'm sure that the gas mileage is correct.... unless my odometer is working incorrectly. Oh yeah... I typically take off more like a tortoise, than a jackrabbit... that REALLY helps.

Try this for your next tank....
1) Make sure your tires are FULLY inflated to 35psi or better
2) Run with the windows down and the AC off (no fan either... some of the settings engage the AC even when you don't have the button pushed in) as often as you can stand
3) Accelerate VERY slowly (pretend there's a raw egg between your foot and the accelerator)
4) Don't exceed 60 mph
5) Maintain a steady speed as much as possible (this means if traffic is running ~60 mph only go 55 so you never have to stop or slow down, and USE THE CRUISE CONTROL)
6) Avoid driving in the middle of the day if you can since the air is much hotter and has less oxygen in it (it actually makes your engine perform more poorly).

Force yourself to adopt these habits as often as you can stand, and if you don't already do this stuff, I virtually guarantee your mileage will increase a couple mpg (maybe more) on average. Of course, if you're lifted 6" and are running 35" tires, there's no help for you... LOL Even a 2" lift and 31" tires pretty much guarantees you aren't likely to exceed ~21 mpg tops.

BTW, my AVERAGE tank of gas gets me between 18.5 and 19.5 mpg.

Luis

LoganSix · **Posted:** Wed Sep 28, 2005 8:02 am

Tightwadsjeeper wrote:

4) Don't exceed 60 mph

I would be road kill if I did that.
Actually, I find that if I do about 70 mph, I get better mileage than if I do 60-65 mph.

Tightwadsjeeper · **Posted:** Wed Sep 28, 2005 9:36 am

LoganSix wrote:

Tightwadsjeeper wrote:

4) Don't exceed 60 mph

Actually, I find that if I do about 70 mph, I get better mileage than if I do 60-65 mph.

You only THINK you get better mileage at 70. If you use the cruise, and keep your other driving habits consistant you WILL get better mileage at 60 than at 70. I absolutely guarantee it. Unless of course you're getting better than 24 mpg out of YOUR liberty... in which case, tell me YOUR secrets for better mileage. :lol:

FlaJeepDiver, I know what you mean about the heat... this was the first trip in awhile that I've taken with the windows down... I live in Tampa myself and know all about Florida's heat and HUMIDITY.... we only have three types of humidity here... "Raining", "Just Rained", and "feels like it's Just about to Rain... even if it doesn't actually rain."

Luis

carroll952 · **Posted:** Wed Sep 28, 2005 10:35 am

About the speed thing, I'd say it's probably best to do whatever traffic is doing, anything else would be rather unsafe. A personal preference of mine, I'd rather be driving near someone who is speeding than going below the speed limit.

However here there are only 3 places on the highways where the speed limit is as high as 60mph, everywhere else is 55mph, and people seem not to be in a hurry when they drive in Hawaii.

Justin

LoganSix · **Posted:** Tue Oct 04, 2005 2:28 pm

Tightwadsjeeper wrote:

You only THINK you get better mileage at 70. If you use the cruise, and keep your other driving habits consistant you WILL get better mileage at 60 than at 70. I absolutely guarantee it.

So, when the little numbers for my gas mileage go up when I am cruising at 70 instead of at 60, it's just in my imagination.

The speed limit is 65 mph near me and 70 on other parts down the road. If I drove 60 around here on I-40, I probably would get great gas mileage for a while, as the semi behind me would drag me on his bumper for about a 1/4 mile. :lol:

Jeepjeepster · **Posted:** Fri Oct 14, 2005 11:35 pm

i dont worry about the gas mileage, i worry about wear and tear on the a/c, i want it to last along time, so if its cool outside, i roll the windows down. who cares about gas milesage, u drive a jeep!

freetolio · **Joined:** Tue Aug 09, 2005 11:47 am **Posts:** 38

Generally, lower speed = better gas mileage, but it depends on the speed at which the OD gear kicks in. Gas is most definitely saved when the overdrive gear is activated in an auto. However, that gear is activated somewhere around 50mph in most vehicles.

Windows Open VS Air

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