Why is my '07 getting 12.5 mpg....after a "tune up"? - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 12 (permalink) Old 07-09-2016, 03:39 PM Thread Starter
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Why is my '07 getting 12.5 mpg....after a "tune up"?

Hello!

I hope someone can help me with this. I have a 2007 Sport with only 58,000 miles on it, since I drive other vehicles. I drive a mix of city/country driving.

I took it to a friend's cousin's shop for oil change. He also tightened the plugs. After he serviced it, it is getting 12.5 whopping miles to the gallon. Prior to that, it was serviced last year at the dealer. I need to check my records, but I'm pretty sure they changed the fuel filter and for sure they updated some software that the other dealer had failed to update. Gas mileage briefly went down from 14 to 13 mpg. MPG stayed at 13. Yesterday I drove it for the first time since "the cousin" messed with it, and I see the MPG is down to 12.5.

What are the possible reasons for my truck to get such bad gas mileage? I'm wondering about the fuel filter. I also drive a Chevy 3500 dually. I purchased a fuel filter at Napa and had it installed at my mechanic. MPG went down. Turns out the Napa fuel filter is smaller than a OEM filter, and that is the reason for decreased MPG. With my Commander, the MPG went down after being at the dealer. If they changed the fuel filter (pretty sure they did), I'd expect they'd use the correct fuel filter, but who knows.

Does anyone have any ideas as to why I am getting such bad gas mileage and how I can improve it?
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post #2 of 12 (permalink) Old 07-09-2016, 06:30 PM
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None of the Commanders get great gas mileage.

Mine fluctuates from around 13 MPG in stop & go local driving to 19-20 MPG on the highway, depending on the driving conditions.

The first and most obvious question would be what engine/powertrain do you have?

3.7L V-6; 4.7L V-8; 5.7L V-8?

Are you running stock size tires? Or do you have larger size, aftermarket tires?

Is your Commander lifted - or at stock ride height?


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Last edited by Big Blue; 07-09-2016 at 06:45 PM.
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post #3 of 12 (permalink) Old 07-09-2016, 07:29 PM
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I also believe that the computer updates itself so quickly that at least in our case you can be getting 17-18 mpg and the do some slower driving and make a couple of jack rabbit start and it will drop instantly 2 mpg. Have you tried resetting the gas mileage counter? trhat will give you the right now as it is you are seing the average since it was last reset.


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post #4 of 12 (permalink) Old 07-14-2016, 02:54 PM Thread Starter
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Hi Big Blue and 2010 Inferno,

Thanks for your replies! So, check this out: My MPG went from 12.5 to 15.6 on a mini road trip that I took up to Washington two days ago. I am wondering if this was due to the plugs getting tightened? This was my first trip more than the 3 short drives (15 minutes) that I've taken since this tune up. My trip was all freeway driving. Yesterday, I drove around town and the MPG is still high (for me), averaging 15.2. I am pretty darn ecstatic that my truck is getting such "high" gas mileage now. LOL!

Sadly, I cannot recall my Jeep have such great gas mileage! It has always been serviced at the deal(s). Last year is when the dealer changed the plugs. I notified them that my MPG had gone down. They said it was normal and would go back up. Well, it never did. It maxed at 13.1 MPG for the last year.

Big Blue: no, it's not lifted. Yes, I have after market tires. They are low profiles and larger than stock. I'm pretty sure they are 19" (I will measure and let you know).

2010 Inferno: The computer required upload of some software that the other dealer had failed to update, and then the 2nd dealer charged me. (wtf). This was done at the same time last year as the plugs, oil change, fuel filter change, and I believe air filter change. And then MPG went down. I have not tried resetting the gas mileage counter, but I'll try that and see if it's even better than the 15.2-15.6.
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post #5 of 12 (permalink) Old 07-14-2016, 03:13 PM
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Quote:
Originally Posted by Sundance View Post
Hi Big Blue and 2010 Inferno,

Thanks for your replies! So, check this out: My MPG went from 12.5 to 15.6 on a mini road trip that I took up to Washington two days ago. I am wondering if this was due to the plugs getting tightened? This was my first trip more than the 3 short drives (15 minutes) that I've taken since this tune up. My trip was all freeway driving. Yesterday, I drove around town and the MPG is still high (for me), averaging 15.2. I am pretty darn ecstatic that my truck is getting such "high" gas mileage now. LOL!

Sadly, I cannot recall my Jeep have such great gas mileage! It has always been serviced at the deal(s). Last year is when the dealer changed the plugs. I notified them that my MPG had gone down. They said it was normal and would go back up. Well, it never did. It maxed at 13.1 MPG for the last year.

Big Blue: no, it's not lifted. Yes, I have after market tires. They are low profiles and larger than stock. I'm pretty sure they are 19" (I will measure and let you know).

2010 Inferno: The computer required upload of some software that the other dealer had failed to update, and then the 2nd dealer charged me. (wtf). This was done at the same time last year as the plugs, oil change, fuel filter change, and I believe air filter change. And then MPG went down. I have not tried resetting the gas mileage counter, but I'll try that and see if it's even better than the 15.2-15.6.
What size tires do you have? The round black rubber things that touch the ground (you mentioned 19"... that's your wheel size, which btw bigger heavier wheels don't help mpg). On the tire you should see a number that looks like 255/70r18. Yours will be different numbers but in the same format. Your computer calculates mileage based off of tire size. If you have changed from stock then you cannot use it to calculate your mileage. It can be notoriously wrong on these vehicles anyways. You should hand calculate it.


Avg calculated mileage went up on your trip because it was all highway mileage....

I average 17.5mpg currently with my commute. My wife used to commute in the XK and was getting 18.5MPG when it was slightly lower and still had the front lower air dam on it.

Last edited by luckyse7ens; 07-14-2016 at 03:17 PM.
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post #6 of 12 (permalink) Old 07-14-2016, 04:31 PM Thread Starter
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Quote:
Originally Posted by luckyse7ens View Post
What size tires If you have changed from stock then you cannot use it to calculate your mileage.


Then why would you insist to know my tire size?

Like I said, I do not have stock tires. Nor do I have stock wheels. (19" is indicative that neither tire, nor wheel is stock).
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post #7 of 12 (permalink) Old 07-14-2016, 05:24 PM
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Quote:
Originally Posted by Sundance View Post
Hi Big Blue and 2010 Inferno,

Thanks for your replies! So, check this out: My MPG went from 12.5 to 15.6 on a mini road trip that I took up to Washington two days ago. I am wondering if this was due to the plugs getting tightened? This was my first trip more than the 3 short drives (15 minutes) that I've taken since this tune up. My trip was all freeway driving. Yesterday, I drove around town and the MPG is still high (for me), averaging 15.2. I am pretty darn ecstatic that my truck is getting such "high" gas mileage now. LOL!

Sadly, I cannot recall my Jeep have such great gas mileage! It has always been serviced at the deal(s). Last year is when the dealer changed the plugs. I notified them that my MPG had gone down. They said it was normal and would go back up. Well, it never did. It maxed at 13.1 MPG for the last year.

Big Blue: no, it's not lifted. Yes, I have after market tires. They are low profiles and larger than stock. I'm pretty sure they are 19" (I will measure and let you know).

2010 Inferno: The computer required upload of some software that the other dealer had failed to update, and then the 2nd dealer charged me. (wtf). This was done at the same time last year as the plugs, oil change, fuel filter change, and I believe air filter change. And then MPG went down. I have not tried resetting the gas mileage counter, but I'll try that and see if it's even better than the 15.2-15.6.
If you tires are not stock size, and they are larger than stock - that will throw your mileage calculator/trip calculator off, which means the MPG readings/calculations your computer is giving you will not be accurate - unless you bought an after-market tuner to recalibrate your computer for the larger tire size.

I think that's probably the same point that luckyse7ens was going to make, when he asked you about your tire size.

Secondly, always reset your MPG calculator anytime you start a long trip if want to check your mileage; This will ensure that you delete any old MPG data from previous driving and get the most accurate MPG calculations for that particular trip.
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Last edited by Big Blue; 07-14-2016 at 05:33 PM.
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post #8 of 12 (permalink) Old 07-14-2016, 06:28 PM
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Originally Posted by Sundance View Post
Then why would you insist to know my tire size?

Like I said, I do not have stock tires. Nor do I have stock wheels. (19" is indicative that neither tire, nor wheel is stock).
I need to know your current, not stock, tire size in order to show you the difference in MPH than your original factory tires. This can either confirm or disprove that the DIC is not correct for this reason.

I know what the vehicle came with from the factory.


Quote:
Originally Posted by Big Blue View Post
If you tires are not stock size, and they are larger than stock - that will throw your mileage calculator/trip calculator off, which means the MPG readings/calculations your computer is giving you will not be accurate - unless you bought an after-market tuner to recalibrate your computer for the larger tire size.

I think that's probably the same point that luckyse7ens was going to make, when he asked you about your tire size.

Secondly, always reset your MPG calculator anytime you start a long trip if want to check your mileage; This will ensure that you delete any old MPG data from previous driving and get the most accurate MPG calculations for that particular trip.
nailed it
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post #9 of 12 (permalink) Old 07-14-2016, 07:05 PM
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Join Date: Apr 2014
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Quote:
Originally Posted by Sundance View Post
Hello!

I hope someone can help me with this. I have a 2007 Sport with only 58,000 miles on it, since I drive other vehicles. I drive a mix of city/country driving.

I took it to a friend's cousin's shop for oil change. He also tightened the plugs. After he serviced it, it is getting 12.5 whopping miles to the gallon. Prior to that, it was serviced last year at the dealer. I need to check my records, but I'm pretty sure they changed the fuel filter and for sure they updated some software that the other dealer had failed to update. Gas mileage briefly went down from 14 to 13 mpg. MPG stayed at 13. Yesterday I drove it for the first time since "the cousin" messed with it, and I see the MPG is down to 12.5.

What are the possible reasons for my truck to get such bad gas mileage? I'm wondering about the fuel filter. I also drive a Chevy 3500 dually. I purchased a fuel filter at Napa and had it installed at my mechanic. MPG went down. Turns out the Napa fuel filter is smaller than a OEM filter, and that is the reason for decreased MPG. With my Commander, the MPG went down after being at the dealer. If they changed the fuel filter (pretty sure they did), I'd expect they'd use the correct fuel filter, but who knows.

Does anyone have any ideas as to why I am getting such bad gas mileage and how I can improve it?
I am Curious what tightening the plugs means. Replaced them? When was the last time they were replaced? That would be one of the first things that I would address. That and check your filter. Seems obvious but people overlook it.


Also do you spend a lot of time with the vehicle sitting and idling? Either warming up in the winter or getting the ac going in the summer? That gets calculated by the computer as fuel burned and 0 miles driven and will significantly bring down your MPG rating on the DIC.
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Last edited by luckyse7ens; 07-14-2016 at 07:27 PM.
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post #10 of 12 (permalink) Old 07-14-2016, 09:30 PM Thread Starter
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Quote:
Originally Posted by Big Blue View Post
If you tires are not stock size, and they are larger than stock - that will throw your mileage calculator/trip calculator off, which means the MPG readings/calculations your computer is giving you will not be accurate - unless you bought an after-market tuner to recalibrate your computer for the larger tire size.

I think that's probably the same point that luckyse7ens was going to make, when he asked you about your tire size.

Secondly, always reset your MPG calculator anytime you start a long trip if want to check your mileage; This will ensure that you delete any old MPG data from previous driving and get the most accurate MPG calculations for that particular trip.


Hi. Thanks for your response. I've had these after market tires and wheels on it for almost 3 years. Aside from that, my truck is all stock.

I've driven the same route on my mini road trip before, and always got 13.1. The only thing that changed was the non-dealer tune up.
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