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Old 09-06-2010, 02:37 PM   #1
steves1967
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Help me get better fuel mileage

I know it's been said/asked a million times. But 9mpg on my 97 K3500 dually sucks- and it's even worse when I pull my travel trailer. The family and I are planning a 4000 mile trip this coming spring. If I could get 2-3 mpg better I'd be happy! The truck is all stock at this point. Here is what I was thinking:

Cowl hood- to reduce under hood temps
Shorty headers- ceramic coated to keep heat in
Some kind of new air intake
throttle body spacer
Swap out the factory cats for some high flow units
Royal purple trans and diff fluid
performance computer program (hypertech, etc.)

I thought about pulling the cats out all together- but I dont want any check engine lights popping up either...

Thanks for the help!
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Old 09-06-2010, 02:49 PM   #2
mrh33916
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Re: Help me get better fuel mileage

The rear end gear is what's killing you,

But, if you change the gear will it still pull your trailer?

I don't know if there is a gear set lower than a 4.11 that is available for the rear end in these duallys (maybe someone who knows can chime in) but if mine ever pop's I'll look to go to maybe a 3.73
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Old 09-06-2010, 07:19 PM   #3
steves1967
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Re: Help me get better fuel mileage

I might try a slighty taller tire on the rear of the truck, but as it is the truck pulls fine, might be towards the top of it's capacity though. The trailer is around 9300lbs...
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Old 09-06-2010, 07:43 PM   #4
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Re: Help me get better fuel mileage

9 mpg? Man. That's a fuel sipper! My dually will get 6 unloaded, downhill with a tailwind!
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Old 09-06-2010, 08:11 PM   #5
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Re: Help me get better fuel mileage

A 1 ton dually with a 454 is not going to get good mileage. It is a big, heavy truck designed to work. A fresh set of plugs and wires may help. A performance tune may help in the power area but not increase mileage. 4:11 gears are fairly steep but required for pulling power. A taller rear tire will make a small difference in ratio that may not yield any increase in mileage.
A few things that will make a difference are:
Front end alignment
Fresh tune up
Max air pressure in the tires
Remove any unnecessary weight
Wash and wax dont' hurt either
And slow down, 65 or less
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Old 09-06-2010, 08:36 PM   #6
Shyguy
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Re: Help me get better fuel mileage

This is the setup I have. It is a '92 GMC K-3500 with a 454 and 4L80e. I pull a 8400 pound 5th wheel travel trailer.

If I run right at 58 mph using a deflector wing on the top of my truck while towing I get an average of 8 mpg. If I am running empty the best it has ever got was 12.5 mpg running 58 mpg.

My truck is stock except for a performance chip. It has 4.1? rear gears.

454s are not known for fuel economy.

You could put a gear vendor over-drive behind the transmission, but that gets pricey and it takes a long time to recoup the cost of the over-drive with increased gasoline mileage.
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Old 09-06-2010, 10:08 PM   #7
steves1967
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Re: Help me get better fuel mileage

I was really hoping for the magic cure all But I know I'm in a losing battle with the gas station. If nothing else I really want to lower the under hood temps.

How about swapping the mechanical fan for an electric fan? Or is that not a good idea when towing??
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Old 09-08-2010, 12:18 PM   #8
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Re: Help me get better fuel mileage

I don't know if this will help, but here goes. I have a 91 silverado with a 5.7, 700R4 tranny, and a 3.42 posi rear end running 28" tall tires. I get 20 MPG in daily driving and I live in the middle of Kansas, so the driving is mixed city and highway. I run 75 MPH on the open highways and drive in all kinds of weather hot, cold rain, or snow.

I have an Airaide brand TBI spacer under the throttle body to get more torque and I also run a MSD 6AL spark control and MSD low resistance spark plug wires to get the most out of every gallon of gas. I believe that the MSD items have payed for themselves in the time that I have had them in the truck. The TBI has a 4" tall round K&N air cleaner on it, Maybe some more gain could be realized from a air tube vice the air cleaner, but it would only be on really hot days. The stock fan was replaced by a pair of electric fans and that in itself was a 1 MPG gain. The engine works well without the extra drag on it. I have Edelbrock shorty headers to the 3" single tube feeding a Flowmaster dual 2 1/2" outlet muffler. This engine has 297,000+ miles on it and runs very well. With the tire and rear end combination, I run around 2000 RPMs at about 70 MPH. I also run with a cover on my bed to lessen the air drag.
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Old 09-08-2010, 05:26 PM   #9
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Re: Help me get better fuel mileage

^ thats about the same set up i have minus the tb spacer and im getting about 12 with 35's and 4.10s thats a mix of highway and city driving with the fans and some fuel treatment i picked up 2 mpg i was getting 10 for the longest time, loaded unloaded driving like a grandma or driving like i stole it
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Old 09-08-2010, 05:41 PM   #10
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Re: Help me get better fuel mileage

sorry double post

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Old 09-08-2010, 11:38 PM   #11
steves1967
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Re: Help me get better fuel mileage

I really like that dual electric fan setup. Did you make that yourself or can I buy one somewhere? I didn't even think about adding the MSD ignition. I have all the parts in the garag so I guess it's time to get busy!!

Thanks!!!!!!
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Old 09-09-2010, 10:56 AM   #12
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Re: Help me get better fuel mileage

That fan setup is a SPAL 11" dual setup that can be ordered from Summit Racing under the "BeCool" line http://www.summitracing.com/parts/BCI-75007/

I have the same fans in my 84 GMC and have never had issues with the fans themselves. The setup comes with the shrouds and the are easy to install. If you look close, you can see that I used some strap mill stock that is available from any hardware store chain. I cut to runners that go from the top to the bottom and then connected the cross-pieces to them that hold the fans in place. If I want to remove the fans, four nuts and unplug them, they are out and on the shop floor.

I use a SPAL PWM fan controller, but there are many other ways to control them. While on the Hot Rod Power Tour, the 84's fan controller got water in it, and I had to jury rig the fans in the middle of Birmingham Alabama's cruise night.

The fan controllers that I use allows one fan to come on and then if the temps continue to increase, the second fan comes on, too. For the most part the second fan never runs. To limit the wear on the fan motors, I swap the plugs each winter, so that the opposite fan runs each year.
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Old 09-10-2010, 08:10 PM   #13
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Re: Help me get better fuel mileage

Quote:
Originally Posted by 1badgmc View Post
9 mpg? Man. That's a fuel sipper! My dually will get 6 unloaded, downhill with a tailwind!
6?! Thats freaking sweet

Tune up is a great start, plugs, wires,cap,rotor,air filter and fuel fiter. Also an induction service, top engine cleaner, and a good fuel system cleaner can help, GM & BG are some of the best, not so big on auto zones weekly special. Just my 2 cents
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Old 09-12-2010, 02:39 PM   #14
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Re: Help me get better fuel mileage

Swap in a Cummins. That should get you in the 15 mpg range.
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Old 09-12-2010, 09:38 PM   #15
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Re: Help me get better fuel mileage

[QUOTE=BIGphillip79;4186235]Swap in a Cummins. That should get you in the 15 mpg range.[/QUOTe

There was an old Willys Jeep carryall at the truck show this weekend that had a Cummins in it. The owner stated that it got 26 MPG with the whole thing weighing in at 6000#.
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Old 09-15-2010, 09:25 PM   #16
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Re: Help me get better fuel mileage

This will get you 15-20 mpg:

Get a 6.2L or 6.5L diesel, and swap

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Old 09-15-2010, 09:29 PM   #17
Colt Cobra
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Re: Help me get better fuel mileage

I just change my plugs, wires rotor and cap and added some Lucas Fuel System cleaner to mine and my avg went from just under 7 to just over 9, I was happy. last tank I didnt use the Lucas and it fell back to 8
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