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fishrman
Dodge Dakota
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10/20/2005
20:11:57

Subject: Best Ways to Improve Fuel Mileage
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I recently bought a '99 Dakota 3.9 v6 ext. cab 4x4. I am getting 15.5 mpg which I thought was pretty low for a v6. What are you guys doing to increase mileage. Have read about adding a 180T thermostat and 3923 Autolites, what do these do? Other mod ideas appreciated. already added the K & N drop in. thanks.



daddio
Dodge Dakota
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10/20/2005
20:44:27

RE: Best Ways to Improve Fuel Mileage
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1) make sure the trucks in the best possible state of tune. i.e., good O2 sensor, cap and rotor w/brass contacts, good set of wires & plugs, etc, etc......
2) check your tire pressure at least every 2 weeks.
3) if you have the aux electric fan, loose the clutch fan. with a 180 stat you shouldn't need it.
4) use synthetic fluids in everything, trans, diffs.

is this an auto? i have a manual trans '00 QC and unless i need to, which isn't too often, i don't rev past 2500 rpm.

if you don't like my suggestions you can search the board. this topics gots hundreds of posts.
good luck in your quest for beter mileage.



OBIO3
Dodge Dakota
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10/20/2005
20:47:56

RE: Best Ways to Improve Fuel Mileage
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if it isn't pinging use the stock plugs> colder plugs may run a bit better (unnoticable) on the highway but worse in town > again almost unnoticable > the one thing that no one ever mentions in here about plugs > changing heat ranges is not a perfect answer > lower heat range is a bit better on the highway but a bit worse in town > going hotter is better in town but a bit worse on highway > changing your spark gap is the only spark plug modification that works on both end of revs > open the gap about 10 thousands wider then stock and you get a hotter spark > voltage does not fire plugs > current does > the longer it takes the currant to jump the gap the hotter the spark > remember > this has nothing to do with a plug being hot or cold > hot or cold refers to heat transfer from the plug to the head to the water jackets



Gunner
Dodge Dakota
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10/20/2005
22:34:20

RE: Best Ways to Improve Fuel Mileage
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Get a 48mm throttle body from someone like daveshotdako on this board. I did and I not only noticed an increase in performance, but gas mileage too. I used to get 14.2 MPG, and after the TB install, I now get 16.5-17 MPG. Definately worth the money. Look for his thread about his throttle bodies in the V6 Forum--the thread is called "custom throttle body boring".



95V6
GenII
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10/21/2005
03:12:42

RE: Best Ways to Improve Fuel Mileage
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I actually would be quite happy with 15.5mpg. My 3.9L V6 auto 4x4 gets 14mpg. BTW the official EPA for this truck is 15/19mpg. And EPA numbers are usually better than reality.

95 3.9L 4WD V6, K&N, Gibson exh, JBA hdrs, JET stage II, MSD 6A and more..

N56629
Dodge Dakota
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10/21/2005
06:35:47

RE: Best Ways to Improve Fuel Mileage
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"voltage does not fire plugs > current does >"

Is that why your coil produces very high voltage at very low amperage?



Bob Lincoln
Dodge Dakota
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10/21/2005
08:03:38

RE: Best Ways to Improve Fuel Mileage
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OBIO3 has a poor understanding of electricity. Voltage is electrical pressure, and current is electron flow. "High current" means faster electron flow. Higher voltage is required to jump wider gaps. Low voltage will result in a weak spark.

A 180 degree thermostat will HURT gas mileage and emissions, and improve power slightly, by making the engine run richer.



suggestion
Dodge Dakota
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10/21/2005
09:32:23

RE: Best Ways to Improve Fuel Mileage
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And no offense, but it is really hard to follow his random thoughts separated by all the >>>>.



ObieWonDakota
Dodge Dakota
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10/21/2005
10:08:09

RE: Best Ways to Improve Fuel Mileage
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Don't take this as being sarcastic, but besides the K&N drop in, I slowed down. It works, but then again, most of my miles to and from work are highway miles.



OBIO3
Dodge Dakota
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10/24/2005
05:16:47

RE: Best Ways to Improve Fuel Mileage
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Bob > I do not disagree with your statement > With do respect here assumimg your ignition system, battery and charging system are working proper the coil can only put out the voltage it is designed to do > By opening the gap you can delay the currant flow to allow it to build a better spark and improving the duration of this spark to fire the air/fuel mixture better > I'm not the smartest guy in the world but this works well for me and been doing it for many many years >



prodak
Dodge Dakota
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10/24/2005
14:35:38

RE: Best Ways to Improve Fuel Mileage
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fishrman-

--Unless you have internal mods stick with a factory equivalent plug. They have an extended tip which, theoretically at least (uh oh, here we go) puts the spark closer to the center of combustion (and Dodge among others seem to think this is a good idea). As OB103 correctly stated, you don't need a colder plug unless you have detonation.

--The 180 T-stat may or may not affect your mpg. I'm getting 25mpg highway with a 180 stat in a 99 3.9 so I don't believe it's hurting me at all, YMMV.

--I also have a more open airbox (w/stock paper filter) and V8 TB to which I attribute a lot of the mpg results (and if want max mpg let it suck hot engine compartment air).

--I agree with the synthetics recommendation (motor and rear end at least).

--Another thing I do is keep tires inflated to the maximum psi as stated ON THE TIRE. I know people are gonna say you'll get excessive center-tread wear that way but I've done it on all my vehicles for 30 years and always wore fairly evenly, but that depends on your individual application I suppose.

--I still have original muffler but when it needs replacing I'll go with a not-too-loud performance muffler, that's supposed to help some on these engines.


As to the whole plug gap voltage/current discussion, the wider gap doesn't delay current flow, it basically trades peak current for longer duration spark current, resulting in a bigger flame front, blah, blah, etc. The downside to a larger-than-stock gap (w/stock ignition) is high rpm rolloff, but if, like me, you rarely get above 3500 or so it's a non-issue.



.boB
Dodge Dakota
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10/25/2005
01:04:12

RE: Best Ways to Improve Fuel Mileage
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This is going to sound stupid, but it works.

I drive 5.5 miles to work every day; only 11 miles round trip. All of it city/suburbia streets. I drive against the general flow of commuting traffic, so I don't have to fight traffic much. It take me at least 20 minutes to go that 5.5 miles, and often takes 30 minutes. Do the math on that one.

My 2001 QC 5.9 4x4 with 3.92 LSD rear gets about 11mpg on this commute. Always has, and (I thought) always will. Gas was $1.25, so just drive the truck and live with it. Now gas is $3.00 a gallon. So I had to do something. It's either feed the truck, or feed me.

So I started shutting the engine off. I go through about 4 major intersections. I usually get there just as the light turns yellow - it's my ka. So I have to sit there and wait, and these cycles can be long. SO I started shutting the engine off whenever I cought the yellow. MY mileage went from 11 to 16 in one week! That's almost a 50% improvement. And all of theat fuel was being wasted sitting at a traffic light. BTW, this is the major gas saving technique used by hybrid cars.

Will it wear out my battery and starter sooner? Sure it will. But at 75K miles, it's getting about time to replace them anyway. And it's a trade off. If I can save almost 50% of my fuel bill, I can afford the new battery (that I need anyway).




toolfan
Dodge Dakota
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10/25/2005
01:09:01

RE: Best Ways to Improve Fuel Mileage
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don't drive!



fishrman
Dodge Dakota
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10/25/2005
14:45:16

RE: Prodak
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--I also have a more open airbox (w/stock paper filter) and V8 TB to which I attribute a lot of the mpg results (and if want max mpg let it suck hot engine compartment

Prodak, what is a v8TB?

thanks



prodak
Dodge Dakota
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10/25/2005
15:15:28

RE: Best Ways to Improve Fuel Mileage
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fishrman-
Sorry, TB=throttle body.
The 3.9L TB is interchangeable with the 5.2/5.9L ('97 and up in your case), only difference being the bore sizes. Pretty much anything that gets more air into the 3.9 is going to help (up to a point). By switching to a larger-than-stock TB you're trading a little off-idle response for a noticeable midrange and top end improvement and usually, but not always, a slight bump in mpg. It's a cheap, easy swap that yields uber bang-for-the-buck.



OBIO3
Dodge Dakota
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10/25/2005
22:58:55

RE: Best Ways to Improve Fuel Mileage
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PRODAK >>>>>> I agree totally with you except the delay part > Although the delay is unnoticable to us it actually is there > The wider gap needs a tad more voltage buildup prior to currant making the jump and yes this gives better duration > Even gaped normal there has been a lot of statements about lack of performance at about 5000 > Talking prior to the ignition shutdown > Stock or standard coils fall off at high RPM > Best bang for the buck is a coil that puts out 28 to 30,000 volts > Is oil filled and has a metal case for best heat disapation > This coil will have an active magnetic core and should be identified with words such as controlled output, veriable magnetic or automatically controled or other words that refer to these effects > The very first thing I do when I buy an auto is a good tunup plus one of these coils > Only way to fly



prodak
Dodge Dakota
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10/25/2005
23:24:26

RE: Best Ways to Improve Fuel Mileage
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OBIO3-
I think we're saying the same thing, I just disagree a wee bit with your terminology.
Strictly speaking, delaying current flow and slowing current flow are not the same thing. Not being an EE I can't say there isn't a few nanoseconds of delay, but even if there is that's not the operative factor here. What IS happening is that the larger gap presents a higher resistance, reducing spark current thereby taking longer to discharge the available (coil) voltage. Other than that I think we're in total agreement.



prodak
Dodge Dakota
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10/25/2005
23:44:05

RE: Best Ways to Improve Fuel Mileage
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BTW, the "voltage buildup" you're talking about is actually coil rise time.



OBIO3
Dodge Dakota
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10/26/2005
01:02:25

RE: Best Ways to Improve Fuel Mileage
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I know > and your right > were in the same boat just not side by side lol




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