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Regular Service / Maintenance This section contains discussion about regular service and maintenance (upkeep) of your Jeep Commander

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post #1 of 11 (permalink) Old 02-08-2011, 05:27 PM Thread Starter
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Gas Mileage

My '08 Commander with 45k miles was averaging 11mpg in the city and around 16.5mpg on the hwy. No, I don't have a heavy foot and I use the manual shifter to down shift a lot. I decided to replace my spark plugs with platinum plugs. The change has paid off. I am now averaging a little over 12 in the city and right around 18 on the hwy. Next on my list is to get some new tires. I'm interested to see what that gets me.

Cost:
Parts
- 16 Champion Platinum Plugs @ 2.99
- Grease and lube @ 2
Total $53

It took me around 3 1/2 - 4 hours, the back driver side ones were a little bit of a challenge but not as bad as I thought.

2008 Jeep Commander Limited
Engine: HEMI 5.7L
Drivetrain: 4x4
Miles: 50k
MPG: 12/18

Last edited by B00KERS; 02-08-2011 at 05:28 PM. Reason: Formating
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post #2 of 11 (permalink) Old 02-08-2011, 05:30 PM
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Was that your first spark plug change for this vehicle?

-Matt
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post #3 of 11 (permalink) Old 02-08-2011, 05:33 PM Thread Starter
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Yes, it was. The manual says to do it at every 30k, but I waited a little bit and decided to go with 100k plugs.

2008 Jeep Commander Limited
Engine: HEMI 5.7L
Drivetrain: 4x4
Miles: 50k
MPG: 12/18
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post #4 of 11 (permalink) Old 02-08-2011, 05:40 PM
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Good to know.

FWIW, i got 2-3 mpg increase when I replaced my spark plugs at 30k miles... but I used OEM copper plugs. I've noticed this trend on most forums. People replace their original spark plugs with some fancy ones and think that the mpg increase is from the "special" style plug when, in fact, its more likely that the old plugs were just worn.

If you haven't done so already, you're probably due for some fresh diff and t-case fluid. That usually frees up a bit more mpg too (not a lot... but if you're getting 12.8 it may be enough to get you that #13 figure )

-Matt
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post #5 of 11 (permalink) Old 02-08-2011, 06:10 PM Thread Starter
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Good to know, I have that schedule to do at around 60k. I'll make sure I do it. I decided to go with platinum plugs so I wouldn't have to replace them so often. We'll see how that turns out. I'm hoping the tires help out also. I just had to have the dealer replace my mutifunction switch. It went bad and both my levers stopped working.

2008 Jeep Commander Limited
Engine: HEMI 5.7L
Drivetrain: 4x4
Miles: 50k
MPG: 12/18
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post #6 of 11 (permalink) Old 02-08-2011, 06:19 PM
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Yeah you might want to change some of those fluids prior to 60k. For my 2007 the axles are due every 15 and the tcase is due every 30, trans is due every 60. Not sure what the 2008 manual says... it seems like every year there's something different (FYI, it's not very clear if you just browse through it... but just about every driver on the road falls into the "Service B" category for the maintenance; read it carefully). .... I do think 30k intervals are perfectly fine for the axles; but i dont mind doing mine every 15.

Check out the LRR (Low Rolling Resistance) tires on tirerack for some good options there.

-Matt
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post #7 of 11 (permalink) Old 02-09-2011, 09:14 AM
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Join Date: Mar 2008
Location: Annandale, NJ
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The appropriate tire pressure is crucial for good gas mileage, in my experience. When the weather was getting cold last Fall, my tire pressures were dropping to 32-33lbs (cold). My mileage also dropped. When I inflated my tires to 36-37lbs (cold), my mileage improved quite a bit.



2007 Jeep Commander Overland - Steel Blue
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Caroline Driveline front drive shaft
285/70/17 Cooper Discoverer ST Maxx
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post #8 of 11 (permalink) Old 02-09-2011, 10:15 AM
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My XK is supposed to be a flex fuel vehicle, whatever that means.

The are signs at more and more gas stations that are offering E85 fuel.

E85, Flexfuel, as I understand this, is 15% Ethanol. When I went to BP
and some other stations, they say the have 10% Ethanol. So the difference
between fuels is 5% Ethanol. It is no wonder our fuel efficiency sucks.

E85 gets less mpg and costs less. Where the standard fuel 87oct, has

10% Ethanol.


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post #9 of 11 (permalink) Old 02-09-2011, 10:19 AM
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May have found my own answer.......

Ethanol fuel mixtures have "E" numbers which describe the percentage of ethanol in the mixture
by volume, for example, E85 is 85% anhydrous ethanol and 15% gasoline.
I thought it was 15% Ethanol.

E10, sometimes called gasohol, is a fuel mixture of 10% anhydrous ethanol
and 90% gasoline
that can be used in the internal combustion engines of most modern
automobiles and light-duty vehicles without need for any modification on the engine or fuel system.


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post #10 of 11 (permalink) Old 02-09-2011, 10:05 PM
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Fresh plugs will improve mileage that has degraded gradually over the 10's of thousands of miles. Platinum itself will NOT improve the mileage. Of course there are hundreds of different engines and plugs, so its always possible to find one combination that works a little better than others, but usually the general rules hold true.

Like you stated, platinum lasts longer longer than the standard steel electrode plugs.

Problem is, I'm pretty sure all the Commander engines use a wasted spark ignition system, where 2 plugs share a coil. This kind of system has a reverse current flow for half the plugs, and the reverse current flow will reverse the anode and cathode of the plug. Normally the current flows from the Platinum to the Steel, and less metal is carried with the current. Reverse the current flow and it flows from the steel to the platinum and in that case a lot more metal is carried from the steel to the platinum. In short, with a platinum plug, reversing the current eats the steal portion of the steel away much faster than just plain steel plugs.

Double Platinum plugs have platinum on both electrodes, so when you reverse the current flow it still flows platinum to platinum, and NOT from steel to platinum, where it carries a lot of steel with it.

And yes, keeping tire pressure up does a lot to improve mileage, as well as a clean air filter.

Alcohol has about 1/2 the energy density that gasoline does, which means you have to burn twice as much to make the same amount of power. The exact ratio varies with the type of alcohol.

Keep in mind, ethanol in high enough ratio can be corrosive to seals, metals and hoses in the fuel system. So do NOT use E85 unless you confirmed your fuel system is designed to use it. ON top of that, check all the manufacturers recommendations about using E85, other Chrysler Flex Fuel Vehicles, they recommended using a special motor oil with the fuel. I've seen lots of warnings about the alcohol causes wash out of oil on the cylinder walls, blow-by contaminating oil, etc.


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Last edited by Mongo; 02-09-2011 at 10:18 PM.
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