Freaking out here... 8 MPG on the 3.7L - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 16 (permalink) Old 03-19-2015, 06:56 AM Thread Starter
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Freaking out here... 8 MPG on the 3.7L

Hi

I got my Commander a couple of months ago, and the MPG was consistently horrible (mostly 8.3 MPG and some lucky times I get 10) and I don't know whats the problem, its well maintained, no DTC errors at all, instrument panel doesn't show errors, tires at the right pressure,
its really freaking me out since some people say they get 15-16 which is twice as much as I get, and some 20+ .

is there any known issues causing such drastically low MPG.

P.S my foot is pretty light on the gas pedals and the roads I usually use are mostly level.

Specs: 2007 Rocky mountain edition, 3.7L V6, not many options.
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post #2 of 16 (permalink) Old 03-19-2015, 11:07 AM
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That's terrible mileage. I just bought my Commander less then 2 months ago and mine has a 5.7.... but it still gets about 11.3 mpg or so in town.

I'm sure there is either a few usefull threads on that very issue (via the search option) or some knowledgeable guys here will help you out.
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post #3 of 16 (permalink) Old 03-19-2015, 11:46 AM
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My gas mileage after a few months was around 11.5-12.5 but alot of stop and starting at lights and slower traffic. I thought the same thing. So since then I put in a K&N air filter only and like you tire pressures are fine. My gas mileage went up to about 14.3 but sometimes dips below that. I would suggest chling you air filter housing and plugs. My air filter house was absurdly dirty and filter was almost totally plugged. Also Ive read that using synthetic oil on changes helps as well. Thats my next move when its due...I will get a K&N oil filter and buy some Mobil1 synthetic 5w-20 oil. Hoping that will help a little more. Changing the plugs this weekend as it has 61k original miles on them even though garage says they can go 100k I'm not waiting till then as buying from the dealer they really didnt touch much on my XK so Im being pro-active.
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post #4 of 16 (permalink) Old 03-19-2015, 12:25 PM
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Have you hand calculated your MPG?

EVIC (the digital readout) is wrong on many vehicles. If you live in a cold climate and let your vehicle idle to warm up for a long time that effects your MPG. Thats lots of fuel burned and no miles traveled.

Also if you have no changed your plugs yet. Look into that. Every 30k miles ...


I Average 18MPG with a lift and 32" tires. I get 21+ HIGHWAY.


Reset your EVIC MPG readout and see what happens.
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post #5 of 16 (permalink) Old 03-19-2015, 03:29 PM
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Quote:
Originally Posted by Tarik View Post
...I got my Commander a couple of months ago, and the MPG was consistently horrible (mostly 8.3 MPG and some lucky times I get 10) and I don't know whats the problem, its well maintained....
How do you know it was well maintained? You've only owned it a couple of months? Unless you've got some pretty convincing service records, I'd be suspicious.

luckyse7ens has several good suggestions. Clogged up Air Filter or Eroded away spark plugs, 10's of thousands of miles overdue to be changed can cause a drastic decrease in mileage. Unless you've got an unimpeachable record of the plugs/filters being changed and are NOT overdue for a change, I'd be checking those items.

And like people suggested, if you're measuring your mileage just on what the EVIC spits out, you're doing it wrong. You need to do the old Fill your tank, note the mileage, fill your tank, note the mileage and numbers of gallons to fill the tank, do the math. Average it over a couple of dozen fill ups to get an accurate mileage.

Finally learn how to reset the average mileage indicator on the EVIC, if the previous owner never did that, your couple of months of driving is NOT going to make one iota of difference on an average that has been running for 8 years.
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post #6 of 16 (permalink) Old 03-19-2015, 06:26 PM
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Since I bought my Commander I find myself constantly resetting the EVIC so I can get a real feel report on what kind of fuel I'm consuming when on hills, straight-aways, etc.

Its interesting to watch what its showing but like others have already suggested, record your mileage and do the math. For example on my 07 with a 5.7, has a 21.1 gallon tank. My last tank of 87 octane took me about 268 miles till I decided I really need to get fuel. The message on the instrument panel was showing anywhere between 0, 3 and 6 miles left till empty, so I think I ran it within a half gallon of dry. It came out to average like 12.6 miles to a gallon.

I'm sure that when I change my plugs it will give me an improvement...least I hope to get it to around 14mpg average.
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post #7 of 16 (permalink) Old 03-19-2015, 07:03 PM
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The tanks have a about a 4 gal reserve. So when your message says 0 miles or your fuel light comes on you have 4 gal left to run the Jeep. Pretty much we have a 16-17 gal of usable fuel.


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post #8 of 16 (permalink) Old 03-19-2015, 07:10 PM
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Join Date: Apr 2014
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Quote:
Originally Posted by luckyse7ens View Post
Have you hand calculated your MPG?

EVIC (the digital readout) is wrong on many vehicles. If you live in a cold climate and let your vehicle idle to warm up for a long time that effects your MPG. Thats lots of fuel burned and no miles traveled.

Also if you have no changed your plugs yet. Look into that. Every 30k miles ...


I Average 18MPG with a lift and 32" tires. I get 21+ HIGHWAY.


Reset your EVIC MPG readout and see what happens.
I Average 18MPG with a lift and 32" tires. I get 21+ HIGHWAY @~65mph, if your cruise speed is 75-80 your getting worse MPG.

You have a roof rack? Anything on the roof kills highway MPG. I removed my cross bars even.

You have the air deflector under the front bumper in place? I have mine installed.

My XK is 2wd, which is less weight and less drag/driveline loss.

I have a hypertech tuner.

Wheel and tire weight probably contribute I have 18x9's with P255/70r18 Bridgestone Dueler RHS's. A narrower wheel and tire combo would be better, but a less aggressive tread (like mine), and lighter sidewall (P is lighter than LT) are ideal for MPG.

Full synthetic oil. Pennzoil Platinum 5w20 atm with mobil one filter for longer OCI's

New NGK plugs.

Driver MOD: My wife's DD. She has a light foot.


WHen I got this vehicle @~90k with stock height, fortezas, and OLD plugs it averaged ~14mpg.

Each of those things likely add .5MPG or less, but all told it makes a difference.

Last edited by luckyse7ens; 03-19-2015 at 07:34 PM.
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post #9 of 16 (permalink) Old 03-19-2015, 07:37 PM
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Quote:
Originally Posted by SAL-XK View Post
The tanks have a about a 4 gal reserve. So when your message says 0 miles or your fuel light comes on you have 4 gal left to run the Jeep. Pretty much we have a 16-17 gal of usable fuel.

I dont want to hijack his thread, but I didnt realize the tank reserve was that much fuel. If that's the case my 268 miles on a tank ..say I only used 19 gallons or so...which jumps me to about 14 mpg or better. That's more where I thought it should be.

Ok..I'm done thread hijacking now.
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post #10 of 16 (permalink) Old 03-19-2015, 09:07 PM
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Quote:
Originally Posted by BBCBIRD View Post
I dont want to hijack his thread, but I didnt realize the tank reserve was that much fuel. If that's the case my 268 miles on a tank ..say I only used 19 gallons or so...which jumps me to about 14 mpg or better. That's more where I thought it should be.

Ok..I'm done thread hijacking now.
That's not how this works, That's not how any of this works I couldn't resist. You start with a full tank. Then when you fill it up again you divide that number of gallons with you mileage.


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