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Old 06-02-2005, 04:12 PM   #1 (permalink)
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Gas mileage help

Have a '99 3/4ton with 5.9l motor, extended cab, 4X4, auto. This truck only gets 10mpg. Synthetic motor oil and a topper are the only additions. The 10mpg is 90% freeway driving at 70mph. Are there any cheap/simple things I can do to improve the mileage? It has 80,000 miles on it. Tried a K&N filter and the mileage went down even further. Dealer has been no help, now the truck is out of warranty.

Last edited by RDR800; 06-03-2005 at 08:53 AM.
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Old 06-02-2005, 04:24 PM   #2 (permalink)
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Do you mean the 5.9? Use a scan tool and see if any codes come up. That should head you in the right direction at least.
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Old 06-03-2005, 08:57 AM   #3 (permalink)
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Thanks for the tip SD. I will have to go find one(scan tool). The truck also seems to run quite hot. The needle sits right on the 2 of 210. I was wondering if a cooler thermostat would help?
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Old 06-03-2005, 08:59 AM   #4 (permalink)
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Check your fuel pressure as well.
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Old 06-03-2005, 10:35 AM   #5 (permalink)
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it could be high fuel pressure caused by a vacuum leak. Realy common on those trucks.

Also the timing could be off due to a loose timing chain.

Change out those 2 and you will have alot more power and better milage.

That said, my buddys 01 only got about 12-13 on the highway, and 10ish around town with 20k on it. By the time he sold it with around 60k, it was getting around 11 on the freeway.

My half ton gets 10-11 freeway.

It really doesnt sound THAT far off.
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Old 06-03-2005, 12:57 PM   #6 (permalink)
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Quote:
Originally Posted by RDR800
Thanks for the tip SD. I will have to go find one(scan tool). The truck also seems to run quite hot. The needle sits right on the 2 of 210. I was wondering if a cooler thermostat would help?
That's the milage that mine gets and the temp runs the same as yours. I thought that it was running rather cool.

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Old 06-05-2005, 06:10 PM   #7 (permalink)
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I got rid of my 5.9 because of this crap. I had the long bed w/ the 35 gal. tank and could only get 225 miles out of a tank. Granted, I had 4.56 gears and 33's but c'mon...
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Old 06-11-2005, 09:41 AM   #8 (permalink)
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Duct tape and 6" 2x4 block............Tape block under skinney pedal! Best I can do.....Sorry!!!
10 MPG sounds good to me......Try 4-5 MPG and feel MY pain! Good luck.....
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Old 06-15-2005, 08:20 AM   #9 (permalink)
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Umm...what gears? If you have 4.10s, at 70mph you are sucking fuel.

My suggestion would be exhaust if you haven't done that. Try running a little better pressure in your tires. Slow down (if possible).

The 5.9s were not known for their great mileage. With a 318, 265s, 3.55s and an auto I could "squeek" 20 mpg out once in a while...I averaged 15-16mpg. The two best improvements were exhaust and ignition upgrades.

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Old 06-15-2005, 11:43 AM   #10 (permalink)
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This is that I did to get better gas mileage. I went out and bought a 1st gen 4Runner with the 4cyl engine and use that as my daily driver. Now I get around 20 mpg every time!!

Seriously, I have a 99 Ram 1500 4x4 QuadCab with the 5.9L V8 that I nearly piss myself when it hits around 13 mpg (whether I am driving in the city or on the highway, this is what I get). And this was after I went down to 265's AT's (from 285 muds), installed a bigger throttle body, installed an aFe cold air kit, installed a 180 deg thermostat, put headers, high-flo cat, and high flow flowmasters on it, and learned to take it easy on the skinny pedal on the right.
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Old 06-18-2005, 12:16 PM   #11 (permalink)
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My 01 Ram 2500 with a 5.9 also gets 10 mpg. I knew that before I got it though. I only put about 5k a year on it.
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Old 06-20-2005, 08:50 PM   #12 (permalink)
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Trade it in for one with the 5.9 Litre Inline 6.

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Old 06-20-2005, 11:54 PM   #13 (permalink)
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meh i get about 6-8mpg driving around town and about 9-12mpg on freeway..but 3.55's and 35" tires help the gas mileage..on the freeway anyways.
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Old 06-23-2005, 06:50 PM   #14 (permalink)
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I never gave it a thought...most likely it has had the "death flash" done to it...beg. borrow, or steal someones power programmer...I have heard guys having good luck with reprogramming their trucks that have been flashed.

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Old 06-28-2005, 05:47 PM   #15 (permalink)
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Unfortunately power programmers are VIN locked to the vehicle they are first used on. I had the same complaint about my Vortech 7.4 K2500 Suburban, crappy mileage. I added +4 plugs, an MSD 6A ignition, dual flowmasters, a K&N intake, and a reprogramming with a power programmer.

After all the mods it had much more power, much better, firmer shifts, and I was able to squeeze 16 mpg out of it on the highway, a 2 mpg increase. With the money I'm now saving in gas I figure that I'll have paid off what I spent on those mods in 5 to 10 years.
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Old 06-28-2005, 10:21 PM   #16 (permalink)
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Well I have two ramchargers, one with a 440 that gets 7-8, one with a 318 that gets 16 all around, I only drive about 60-65 tops, and hard as it is dont beat the rigs bad. 10 seems about right, but then again look at the weight, roughly 5500 - 6000 lbs?
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