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H2OuUp2
Happy to be here
Premium
join:2002-03-15
Oklahoma City, OK

Why better MPG at 80 vs 70?

I have a 2005 5.7L Jeep Grand Cherokee. I recently had to start going 81 miles one way to work daily so 162 miles per day.

Now I leave at night and drive 80 mph to make the trip in 1 hour, and average 16 MPG.

On the way home I go 70 mph and average 15.1 mpg.

I really thought I would get better mpg going at the lower speed. Just wondering.

Also what suggestions do you have for a good mpg car? I was thinking the Volt, but I hate to wear out a new car so quickly.
--
He is no fool who gives up what he cannot keep, to gain what he cannot lose. - Jim Elliot


Kearnstd
Space Elf
Premium
join:2002-01-22
Mullica Hill, NJ
kudos:1

I think something like the Cruze ECO or a similar car from another company rather than the Volt. in your case you would be on gas most of the time anyway with the Volt.

is there a different in traffic? AC usage habits? is one direction of the freeway nice new smooth paving?

And this may sound dumb, but is it possible the late night air is cooler and effecting MPG due to higher air density.
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports



BonezX
Basement Dweller
Premium
join:2004-04-13
Canada
kudos:1

you got something backwards, more dense air more fuel required to get proper mixture rate.

hence, intercoolers.



Cho Baka
Premium,MVM
join:2000-11-23
there
kudos:2
Reviews:
·TekSavvy DSL
·Cogeco Cable
reply to H2OuUp2

It is extremely unlikely that you get better mileage at higher speeds.
Either one of the two directions is uphill, or you had the wind against you one way.

The Volt is not appropriate for what you are looking for. It isn't notably efficient once the battery is depleted, achieving an "equivalent of 32 mpg on regular fuel".

»www.thetruthaboutcars.com/2010/1···-35-mpg/
--
The talented hawk speaks French.



aannoonn

@optonline.net
reply to H2OuUp2

Did you get gas between the two trips?

I found I get >1 mpg better if I follow something like a big-ass Tahoe by a few car lengths.



bryanviper

join:2002-10-12
Toronto, CAN
reply to H2OuUp2

Check out the VW Jetta TDI
If you are doing highway driving you can get around 1200km/tank
--
»www.MaximumRepair.ca
Computer Repair/Upgrades In Toronto.



H2OuUp2
Happy to be here
Premium
join:2002-03-15
Oklahoma City, OK
reply to H2OuUp2

Thank you for the responses!

Well the AM is very early and it is cooler. Not a lot of traffic so I truly get to cruse, seldom do I ever hit my brakes.

With the PM is traffic I do have a lot of slow down and speed up, so maybe that's it? I don't think it's wind most of the time anyway because it's pretty consistent. I fill up and check the gallons and it always about .9 better. I'll try 70 in the AM one morning and see what I get.

Thanks for the info on the Volt. I really want something that gets good MPG, but won't get you ran over on the interstate. Also I have to consider weather coming up so something that is decent on ice, snow.
--
He is no fool who gives up what he cannot keep, to gain what he cannot lose. - Jim Elliot



CylonRed
Premium,MVM
join:2000-07-06
Bloom County

quote:
With the PM is traffic I do have a lot of slow down and speed up, so maybe that's it?
Yep - that is why it is important to pay attention to the driving conditions and how they are different.
--
Brian

"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain


BonezX
Basement Dweller
Premium
join:2004-04-13
Canada
kudos:1
reply to H2OuUp2

the new imprezas are supposed to be decent on gas (the 2012 model) and other then a world ending event, there's not much weather wise that can stop you.



aurgathor

join:2002-12-01
Lynnwood, WA
kudos:1
reply to H2OuUp2

The air resistance is about 30% (!!) higher at 80 mph vs 70 mph ((80^2)/(70^2)), so something else must've been going on that introduced an error.
--
Arguing with an idiot makes you one.



Cho Baka
Premium,MVM
join:2000-11-23
there
kudos:2
Reviews:
·TekSavvy DSL
·Cogeco Cable
reply to H2OuUp2

said by H2OuUp2:

Well the AM is very early and it is cooler. Not a lot of traffic so I truly get to cruse, seldom do I ever hit my brakes.

With the PM is traffic I do have a lot of slow down and speed up, so maybe that's it?

Yes, traffic is likely the answer to your fuel consumption difference. Every time you step on the brakes you are wasting energy.
--
The talented hawk speaks French.


TheHarvester
Premium
join:2006-08-25
Dana Point, CA
kudos:3
reply to BonezX

But that also equates to less throttle to maintain a set speed.
--
mbsastronomy.com


Kearnstd
Space Elf
Premium
join:2002-01-22
Mullica Hill, NJ
kudos:1

said by TheHarvester:

But that also equates to less throttle to maintain a set speed.

Yes but speeding back up again uses more gas than holding a set speed. Engines are most efficient when running at a constant and stable cruising speed.

my 2000 impala sits around 2300rpm I think at 80 on flat road with the overdrive kicked in.
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports


TheHarvester
Premium
join:2006-08-25
Dana Point, CA
kudos:3

I know this but what does it have to do with my post?
--
mbsastronomy.com


LowRider

join:2006-06-23
Douglasville, GA
reply to H2OuUp2

I was going to say where the throttle is open at but I guess at 70-80mph it's open the same amount of space. You know how people drive there cars with pipes they keep the throttle at a certain point so you can hear them which eats gas to. Not sure if that might have something to do with it at that speed??



michieru
Premium
join:2009-07-25
Miami, FL
Reviews:
·Comcast Business..
reply to H2OuUp2

Look into the following:

Domestics:

Chevrolet Cruze-ECO
Chevrolet Volt
Jeep Patriot
Jeep Compass

Import:

Hyundai Sonata Hybrid
Hyundai Elantra
Volkswagon Jetta TDI
Audi A3
Hyundai Tucson

I included some SUVs in there since you currently own a Grand Cherokee and you probably still want to stick with one.



civicz

@optonline.net
reply to H2OuUp2

First, with out doing the *same* road, with the *same* traffic, your numbers are useless... you also already said more traffic on the way home... doing the 70... brakes are 100% turning your fuel into heat... not speed.

Civic. Volt, lol is a POS for long distances. Honda civic. good mpg, thing lasts forever.



PhoenixDown
FIOS is Awesome
Premium
join:2003-06-08
Fresh Meadows, NY
kudos:1
reply to H2OuUp2

I get good gas mileage out of my 2006 Honda Civic. The hybrid version probably does even better but I imagine it would not be ideal for the kind of travel you are doing.
--
~ Insert a Funny Sig Here ~



EGeezer
zichrona livracha
Premium
join:2002-08-04
Midwest
kudos:8
Reviews:
·Callcentric
reply to H2OuUp2

+1 for the difference being due to different driving conditions.

You could try driving 70MPH to work and see what the difference is between that and driving 80.

It's possible that the engine's power band may be better at the higher speed, compensating for the increased mechanical and wind resistance losses. That's purely speculation, though.

I use the Ecobost HD device to track real time and point-to-point mileage on my car. I've found that despite my best efforts to maintain constant speed, I can't do as well as the cruise control to maximize mileage.

I also found that there's about 5-6 MPG difference between driving 45MPH out of OD and and in OD. that lockup really saves fuel.

With a 160 mile commute, I'd look for a car that's comfortable as well as fuel efficient, and is good for the long haul/high mileage. You're spending about 3 hours a day in it, be comfortable.

I see no reason why you couldn't get over 300K out of a car that you fire up and drive 80 miles at steady legal highway speeds twice a day, and keep it well maintained.

The only hybrid I'd consider would be the Prius. Other than that, a Camry or similar size vehicle. KIA and Hyundai may be cheaper, but for whatever reason, parts and labor on stuff like timing belts, CV assemblies etc seem higher.
--
Follow your dreams, except the one where you're naked in church.



SmokChsr
Who let the magic smoke out?
Premium
join:2006-03-17
Saint Augustine, FL
reply to H2OuUp2

Way back when... I had a Datsun 710, I had a ZT driving computer in it. (this was back when the national speed limit was 55) I found that the car operated most efficiently at 66MPH. At 55MPH the fuel consumption was up about 15%. So I was having to go 55 to save gas.. yea right..

In any case at least with that car there was a specific point where the gear ratio and engine RPM, Vs driving resistance maximized for a peak performance.

Another surprise was when I found out that that using the AC with the window up was more efficient, that no AC and the window down. Mind you No AC and the window up was most efficient, but not practical in Florida.

As others have said your tests are currently inconclusive, once you do a few runs at 70 in the morning, duplicating the 80 runs you'll have the information to determine what's going on.

Gee I miss that driving computer..



CylonRed
Premium,MVM
join:2000-07-06
Bloom County

quote:
Another surprise was when I found out that that using the AC with the window up was more efficient, that no AC and the window down.
Not really - the AC switches on and off that minimizes the extra work done. With the windows down - there is added resistance (drag) all of the time you are moving.
--
Brian

"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain

Kearnstd
Space Elf
Premium
join:2002-01-22
Mullica Hill, NJ
kudos:1

I think the mythbusters even tested that once that the AC is always more efficient than having the windows open.

speaking of the AC, some cars actually cycle it in winter too. the compressor will run with the defroster.
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports



CylonRed
Premium,MVM
join:2000-07-06
Bloom County

To prevent fogging\frosting up on the inside of the windows.



cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to H2OuUp2

The efficiency of the gas engines isn't constant, it depends on the RPM and load. It is definitely possible for the efficiency to be better at the RPM & torque needed for 80mph than at the RPM & torque needed for 70mph.
My Grand Prix is about the same, I get much better MPG at 75mph than at 65.



telco mtl

@blackberry.net

I was going to say the same I've had 2 3.8l v6 grand prix's and (metric) I get better fuel economy at 110km/h than 100km/h and this is realtime measurements with my scanguage II



DadeMurphy
Premium
join:2002-07-25
Danvers, MA
reply to Kearnstd

said by Kearnstd:

I think the mythbusters even tested that once that the AC is always more efficient than having the windows open.

If memory serves me right, I believe the conclusion they came to was under 45 mph you're better off with the windows down, anything over that you're better off with the windows up and the AC on. This magic number of course will be different for every vehicle, but pretty much on highway = AC, around town = Windows.
--
Most people don't think clearly when they're on fire.

prairiesky

join:2008-12-08
canada
kudos:2
reply to H2OuUp2

1) is 1 way up hill and the other down?

2) when i had my 94 grand marquis, the sweet spot for fuel economy was about 80 mph and again at about 55 mph. At 55 i'd get roughly 25 mpg but one long trip down to the US, I was cruising at around 80 and the guage on the dash was showing 33mpg! inbetweeen it varried due to engine speeds but that car was happiest at a nice low rpm of around 1200...



H2OuUp2
Happy to be here
Premium
join:2002-03-15
Oklahoma City, OK
reply to H2OuUp2

The MPG thing is truly baffling. I do however think the power band likes 78-80 the best, it just seems to run with no effort at all at at that speed.

Now. I talked to a person that had a Jetta someone mentioned earlier, and he swore he got 50 mpg making the same trip I'm making. I don't see it, but I'll look

Yes I need comfort, too many hours in the car. Also blue tooth on the Cell phone is a must too much time on the phone to not have it.
--
He is no fool who gives up what he cannot keep, to gain what he cannot lose. - Jim Elliot


prairiesky

join:2008-12-08
canada
kudos:2
reply to H2OuUp2

We took an 06 jetta MT from Winnipeg to Peoria, i think it's about 1400 kms or so, it took us a tank and a half usually going 5 to 10 over the speed limit. I think each tank was $45. it's a very very good car on the highway. they're a little small but not overly cramped. It's a lot smaller than my tahoe, but i've also found jeeps to be pretty cramped, so it might not be that different.