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Hi, I am new to the commander. I am looking to get the most mileage improvement for money spent. I am not wishing to upgrade to 89 or 93 octane gas.


I have been thinking of deleting the mechanical cooling and going with a dual electric fan set up. It has a K n N filter in an oem intake system and stock exhaust. I want to keep it quiet also as it is my girlfriend's. Im in a welding class now and was going to get high flow cats and headers if I can get for cheap as we are both full time college students.

Thanks guys and gals for the input.
 

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The are other threads having to do with mileage on the 4.7 commanders I also have an 06 and the only other thing that got me a slight increase on mpg besides replacing worn sparkplugs was getting the superchips programmer, the economy mode did not do much for me but the 87 performance mode gave me much better throttle response and an increase of about 1.5mpg better with mixed driving city and highway. Now I average about 14.4 wile commuting to work before I was only able to get 12.5mpg.
 

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Full synthetic fluids (trans/diffs/oil). Tune up parts, Catch can (more of an issue with the hemi), tuner.

That should make a noticable difference.

Certainly going to eFans would be something to look into also. Taurus v6 fans are a popular JY pull efan upgrade in general. I can't say I have seen it done on these vehicles personally however.
 

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Once you get all your maintenance up to date and get the proper tire pressure dialed in the biggest gain is driving habits. Driving habits is the always the biggest factor in MPG on anything. I think the new super chips has one those coach modes in it to help you get the best MPG possible. Also most people report the best results with the performance tunes as well.
 

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Cross bars or roof racks will make a noticeable difference as well. I removed my xbars and roof storage and have it stored in my garage.

Fluids, tune up, and tune increased my avg mpg from ~15 to ~18 even though I lifted and am running heavier wheels and tires.
 

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Use the Octane recommended in the owner's manual for the vehicle. Using a lower octane can result in engine damage, possibly serious engine damage. Using lower octane, if you encounter detonation/pre-ignition would cause the PCM to retard the ignition timing and that could result in worse mileage.

Higher Octane fuels, depending one the area you live and the EPA mandated blend of fuel you must have, may have less oxygenated additives in it, that might result in a tiny gain in mileage. Some areas may have the same oxygenating additives as the low octane, and you'll NOT see any gain in mileage. Even if you do see a gain in mileage, its NOT likely to offset the higher cost of the higher octane fuel.

Octane is merely a measure of the burning properties of the fuel, it has nothing to do with the energy density of the fuel, all octanes "should" produce the same amount of energy. I mentioned before, because of various factors and mandated additives, you might find in some areas a barely measureable difference in energy density between octanes. Higher Octane fuels only resist pre-ignition/detonation better than low octane fuels, so if you build a motor with compression and tune to push harder and make more power, it will be more likely to detonate/pre-ignition and thus require the higher octane fuel. The cause for making more power is the motor design, the effect is higher octane, its NOT the other way around.

AFA, headers, custom exhaust and higher performance Catalytic Converters, NOT the way to go, the OEM exhaust is already very free flowing, its doubtful you're going to see any mileage increase by trying to modify it, and then enough to offset the high cost of installing a custom exhaust, but hey, at least it will be more prone to failure and leaks. I'd stick with the other suggestions listed so far. A good tune-up, higher pressure in the tires and mindful driving habits are your best course toward better mileage. The best mod, in my guess, would be one of the programmers that changes the PCM tune, that might produce actual results for the money spent.

The fans? Hmmm, I was under the impression the reason they went with an engine driven fan OEM is because there wasn't room to fit electric fans, perhaps I'm wrong or you can find aftermarket fans that fit?
 

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Just verified in my 06 XK Owners manual that the only engine that is recommend for 89 octane is the Hemi. They state that performance may suffer in the other two engines if higher than 87 octane is used. Page 301 I believe.
 

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From the Owner's Manual (2006):

FUEL REQUIREMENTS
3.7/4.7L Engines (If Equipped)


All engines (except 5.7L engines) are designed
to meet all emissions regulations
and provide excellent fuel economy and
performance when using high quality unleaded
“regular” gasoline having an octane
rating of 87. The use of premium
gasoline is not recommended. Under normal conditions,
the use of premium gasoline will not provide a benefit
over high quality regular gasolines, and in some circumstances
may result in poorer performance.


5.7L Engines (If Equipped)

The 5.7L engine is designed to meet all
emissions regulations and provide satisfactory
fuel economy and performance when
using high quality unleaded gasoline having an octane
range of 87 to 89. The manufacturer recommends the use
of 89 octane for optimum performance. The use of
premium gasoline is not recommended. Under normal
conditions, the use of premium gasoline will not provide
a benefit over high quality regular and mid-grade gasolines,
and in some circumstances may result in poorer
performance.

Light spark knock at low engine speeds is not harmful to
your engine. However, continued heavy spark knock at
high speeds can cause damage and immediate service is
required.

Poor quality gasoline can cause problems such as hard
starting, stalling and hesitations. If you experience these
symptoms, try another brand of gasoline before considering
service for the vehicle.
 

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Chrysler has a general TSB out for complaints about stalling and hard starting in cold weather with cold engines, the first line of the TSB is too ask the owner if they are using higher than recommended Octane Fuel. Higher Octane is less volatile, so it atomizes poorer in cold weather and makes it more difficult to burn, if you're engine is optimized to use a lower octane it could make a difference in cold weather with a cold engine.

Other than that, using higher than recommended octane, by a few points really doesn't hurt, there is really no reason to spend the extra money. There is an argument, that using much higher octane fuel, like race or aviation gas (which some still have lead in them), will burn at a higher temp than the lower octane and might do engine damage. But if you're talking 87 octane is recommended and you put in 93 octane, you're NOT going to hurt anything except maybe harder starter in cold weather. But keep in mind, its NOT going to get you anything either, the engine will NOT make more power just because you put a higher octane in it.

Different mileage with different octanes? I've seen people claim to measure a difference in mileage using a different than recommended octane. Higher, I already mentioned, they are likely to have less oxygenated additives so it might be true, but doubtful it would offset the higher cost. I've seen some claim using lower than recommended octane in other vehicles produced better mileage, in some vehicles under certain conditions, like cooler air temps and lower air pressures, you can safely do this, personally I don't risk it. Likely, with some motors, the better atomization from the lower volatile fuel makes for a slight mileage improvement.

The engines that recommend multiple Octanes, the computer control allows that. Most engines are NOT very resistant to spark knock, the software is written to retard ignition for a few seconds when the knock sensor senses it. The PCM is assuming you're using the correct octane and the spark knock it sensed was a rare condition that it responded to prevent engine damage, it can go back to normal tune after that condition is cleared. In these engines, that recommend one octane, its very possible using a lower than recommended octane, the PCM's retarding of the ignition might NOT be enough to stop the spark knock and the spark knock will continue and damage the engine.

A few engines are tough enough that they can withstand a little spark knock, they write the software so that if spark knock is encountered, it will retard the ignition and engine tune for hours, assuming the owner has used lower octane fuel. That is why the Hemi, and couple other engines, will state you can choose between a higher or lower octane, but if you use the lower octane, you'll likely get less power.
 
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