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Discussion Starter #1
note: Im aware the gas mileage on my vehicle is horrible and knew that before buying it, and I accept it.

08 5.7 Hemi, 17k miles

I'm currently getting 9.5 to 10.5 mpg with 90/10 city/highway mix. Close to all city for the most part with the occasional 20 minute jaunt out to the suburban malls. That "fuel saver" mode is activated and I occasionally see it blink on...I can't imagine it does much and may even experiment turning it off.

Is this about right? 9.5-10.5? I cant find what the city rating is. I've had a dealer oil change service less than 1,000 miles ago fwiw.

If this is not right (and I could only imaging it wrong on the low side) what might I look at? There are no mods.

meegwell
 

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That is about all I ever get driving around in the city with my 07 hemi. I'd say nothing to worry about other than your wallet.
 

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Look for any stored fault codes, make sure you are up to date with preventative maintenance and correct any problems you find with the vehicle. (Spark Plugs and Air Filter are big ones that effect mileage, @17k, your spark plugs should be good, but if you haven't changed the air filter, it could be hurting mileage if its dirty.)

Other than changing your driving style to be more fuel consience, which can be very hard to do in city traffic, that is about all you can do practically.

I guess the Dealer has coupons and cut rates for oil changes to make it economical, usually the dealers charge way to much for other jobs that are NOT worthwhile, which is really frustrating that Chrysler just happens to design the vehicle with proprietary locks that force you to bring the vehicle to the dealer for many repairs.

Personally, I change my own oil, you can use much better synthetic oil and filters for the same cost. Synthetic is arguably overkill, and if you're NOT going to keep the vehicle over 120k miles, that is a good point. If you're going to pay someone else to do all the maintenance and repairs, its usually NOT cost practical to maintain the vehicle to a level to last that it lasts much longer and just get a new vehicle after 120k miles.
 

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Remember, plugs are due every 30k miles OR 3 years, whichever comes first. Stop & Go and idling of city driving takes its toll.... 17-20k city miles are just as bad, if not worse than 30k of highway mileage.

I'd consider a fresh set of plugs and pcv valve (also due every 30k). It sure couldn't hurt, and technically its due.
 

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lol, this thread started out like an AA meeting. "Im aware the gas mileage on my vehicle is horrible and knew that before buying it, and I accept it."

Hi. My name is Ryan. I'm an XK owner and I know It drinks too much.
 

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If you are using premium gasoline, don't. The Owner's Manual says not to use it. 89 octane gas is recommended, with 87 octane being acceptable.
 

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Remember, plugs are due every 30k miles OR 3 years, whichever comes first. Stop & Go and idling of city driving takes its toll.... 17-20k city miles are just as bad, if not worse than 30k of highway mileage.
I think you can make a case that 20k miles of city driving is more like 60k miles of highway. Because its the cold starts and warm-up that are toughest on the motor, and oil, people typical travel 4 or 5 times as far between start-ups on highway miles than city miles, and the time spent, stop and go, braking, accellerating and sitting idling the motor count as well.

jeep5253 said:
If you are using premium gasoline, don't. The Owner's Manual says not to use it. 89 octane gas is recommended, with 87 octane being acceptable.
Yes, higher than needed octane gasoline gets you absolutely nothing, except wasting money. Unless there is something wrong with your vehicle or you modified the motor extremely, or live an extriodinarily hotter and denser air environment than the designers ever envisioned (like Death Valley or Kuwait in Summer), the recommend Octane is more than enough.

People have shown lower octane gets better mileage, my guess, the lower volatility allows better atomization and more efficient burning.

The only way lower Octane is bad, is if you get spark knock, actual detonation, which is really bad for the motor and can damage it, that should NOT happen if you're using recommended octane. The Engine Controller has a safety feature to recognize the spark knock and/or detonation, and retarnd ignition timing to stop it. BUT, retarding ignition timing kills power and power for the amount of fuel burned, resulting in mileage dropping.

So, if your Owner's manual says to use 89 Octane, with 87 Octane being acceptable. That tells me, 89 is best, but the motor will NOT suffer damage if you use 87 octane. I'd measure mileage for both octanes, I would NOT be surprised if the controller has to retard the ignition often for 87 octane, resulting in worse mileage, if it does NOT, which it wouldn't for colder temperatures or higher altitudes, then 87 octane might provide better mileage. Eitherway, measure it and go with the Octane that produces the best for the conditions, don't use octanes outside of what is recommended or acceptable, it can damage the engine. Too high octane, NOT very likely to do any damage, but if it changes anything it will make mileage and cold starting worse, so your just wasting money for worse performance with higher than recomended octane.
 

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Discussion Starter #8
thanks for the input all. My name is Meegwell, and its been about 15 minutes since I last filled up.


Yeah - I justed wanted to make sure that was about right and it should not be something higher like a whopping 11. Wow, 11 mpg, that would be sweet.

So at 40k up front and 40 cents a mile, maybe I shouldn just be taking a cab around town? haha...

My dog loves the commander.


meegwell
 

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I did an extensive mileage test. For my 5.7L and my driving, 91 yielded horrible gas mileage (even when properly tuned for it), 87 was better, but not by much. I get the best MPG and performance running 89 per the manual. (just my experience.... results may vary)
 

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thanks for the input all. My name is Meegwell, and its been about 15 minutes since I last filled up.


Yeah - I justed wanted to make sure that was about right and it should not be something higher like a whopping 11. Wow, 11 mpg, that would be sweet.

So at 40k up front and 40 cents a mile, maybe I shouldn just be taking a cab around town? haha...

My dog loves the commander.


meegwell
Join our HEMI group here---> http://www.jeepcommander.com/forums/group.php?groupid=24
 

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Discussion Starter #12
anyone test or have input on the fuel save (cylinder drop) mode on city driving? this makes sense to me for highway, but I'm not sure with it flicking on and off all the time with city driving it would hurt or help....
 

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Just out of curosioty, since I don't have a Hemi, you can disable the MDS? So that it won't disable half the cylinders?

I could see how, but really don't know, how city driving could cause the MDS to constantly come on and turn off, and how that might be less economical just driving very midly on all 8 cylinders instead.

If that is true, why wait for someone to tell you, do you're own experiment and try it out.
 

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Just out of curosioty, since I don't have a Hemi, you can disable the MDS? So that it won't disable half the cylinders?
No, it can't be disabled. I guess you could do some kind of modification to disable it.
 

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I have the flashpac & yes you can turn off the MDS. I use 91 in the Hemi because I am running the preformance setting in the Flashpac & it asks for the 91. I am getting on average of 10.6 to 11 and it is 85% city driving and I am only @ 37k on it. Now keep in mine the reason I have come up with the MPG being where it is because I have added about 6 to 700 lbs of armor & and also I do have a roofrack with my spare tire up there, plus we are all driving a Box on wheels.
 

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I have the flashpac & yes you can turn off the MDS. I use 91 in the Hemi because I am running the preformance setting in the Flashpac & it asks for the 91. I am getting on average of 10.6 to 11 and it is 85% city driving and I am only @ 37k on it. Now keep in mine the reason I have come up with the MPG being where it is because I have added about 6 to 700 lbs of armor & and also I do have a roofrack with my spare tire up there, plus we are all driving a Box on wheels.
Yea, the Flashpac can make the ignition maps much more aggressive, for extra power, and even a little extra mileage at part throttle, that would require extra octane to prevent spark knock or detonation.

Before I said Heavily Modified, with some of the new engine controllers and devices like flashpac, you wouldn't have to so heavily modify the motor to need to go up in octane, it can change around the tuning of the motor so much, it really does up the pressure and temps in the cylinders to a point a higher octane is needed.
 

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Wow, Im gonna stop complaining about my 15 or so MPG that I now average with a 70/30 city/hwy mix. I used to live out of town and it was reversed and I was seeing 17-18 MPG but that was on roads with speed limits of 55 where MDS was on consistently for long stretches. Also here you rarely sit in traffic.

I do love the Hemi tho! I frequently make road trips on state highways that go through high elevations 5-9K feet above sea level. I take full advantage of the special passing lanes. Even loaded up with adults and kids this thing dosnt even breath hard maintaining 80mph up steep state highways at high elevation.

I have to admit it is one of 3 cars I drive, and it is the thirstiest. If Im just running errands in town I drive a subaru that is fun to drive and it seems like weeks between fill ups. The one complaint I have with the Commander is the small gas tank.
 

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Discussion Starter #19
Just out of curosioty, since I don't have a Hemi, you can disable the MDS? So that it won't disable half the cylinders?

I could see how, but really don't know, how city driving could cause the MDS to constantly come on and turn off, and how that might be less economical just driving very midly on all 8 cylinders instead.

If that is true, why wait for someone to tell you, do you're own experiment and try it out.
I was uner the impression I could disable it in the options but in know way stating I can...just going from memory when I read the manual the first time. It seems like I cant.

Yes, it does flick on and off during city driving quite often.

I was asking for member input from others. Sure I'll check it out myself and wont "wait for someone to tell me" ....the beauty of these forum thingy's is to share experiences! :)
 

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As the MDS goes, if you use the manual shift, it will not invoke MDS.
 
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