I used autolite plugs and 8mm wires and I installed insulation whereever possible to prevent chaffing. My truck only has 115K miles so i am sure as it gets more wear it will get worse. But right now I am dang happy with it. I have put it up for sale becasue i want to build another square body crew cab chevy 4x4 with a cummins turbo diesel. This one will be a custom short bed though.

 

If your going for a project like that. They say a ford body, allison trans, and cummins engine is a great combo.

 

better combo, common rail cummins, 6 speed stick, dodge body, light up like a christmas tree, train horn, full OBA, 100 gallon aux diesel tank, tool box, winch, and some other goodies

as you can see, im already planning for my next truck

 

There is NO reason for that! IF my dink 5.2 on a full 8 foot bed can get at worst 12MPG, then there is no reason why you shouldn't be getting the same. I admit even with driving like a bat out of hell on the last tank, racing at the strip on the same tank, and idling a lot; I got 12.56 MPG. (see below pic) Actually, you should be in the 13-16 MPG range with the 5 speed.
Some ideas-
1. Fuel Injectors
2. Plenum- Even though you did the hughe's kit, doesn't mean it wont ever blow out again.
3. Clogged up catalytic converter
4. PCV valve
5. That 180 stat isn't doing you any favors.
6. Do you idle it a lot? Even just sitting in traffic?
7. Oil weight?
8. Differential fluid?
9. poor fuel?

Another thing that I am a firm believer in; ***** footing around in these trucks don't do squat for fuel efficiency. From my playing around, I think I can conclude that our 5.2 motors do their best when running right around in the 1800-2000 RPM range.

I too was getting around 11 MPG no matter what I did, but through playing around with it, I'm at minimum 12 MPG and my personal best was 16.7. Of course that is on full tank calcs only.
Things I replaced-
1. Spark plugs- started with autolite double plats, then went to the 3293 plug.
2. PCV valve
3. New plug wires
4. K&N drop in air filter- No change
5. Pulled injectors and dropped them off for sonic cleaning and tune.
6. Gutted the cat.
7. New upstream O2 sensor
8. Plenum repair
9. Quit idling it in the mornings to cool/heat up
10. When setting at an extended traffic stop, I kill the motor
11. Tried every single different brand of gas in my local area. I think this last one is the most important. I do not consider all gas to be equal. I don't price shop fuel anymore. I have found that on my motor, I can get the best fuel mileage using Shell 89 octane. That 3-5 cent price hike is actually cheaper if you can get higher MPGs out of it.

Inversely, I've found that my worst mileage came from two gas stations. 1. Casey's and 2. Murphy USA AKA- Walmart.

Look at all this with an open mind, you might be able to bump your mileage a little bit, and learn something about your truck.

 

i got 14 on a 230 mile drive from Kewanee to home, and thats with some hills, and traffic, but when the road was clear i was running at about 65ish, which is about 1800 rpm

 

My truck has 215k miles. It's a completely stock 1500 4x4 with the 318. The plenum is fine (made sure a few days ago). I filled my tank, drove like a bat from hell, filled up when I got empty (I burn 89 octane fuel), and did the math. 12.5 mpg.

 

My truck has 185K , 5.2 , 5 spd man. trans and 3.55 gears . The plenum is now blown (started to ping bad) and burning a fair amt of oil now too . My TB is dirty(shame on me) , I cleaned tha IAC but not the TB portside , it idles rough until I hit the gas when cold . The plugs are NGK FR4's , I'm pretty sure I took the original wires off 2 weeks ago , 2 had been replaced before (different brand) , I did replace the $5 air filter though , lol . The gas filter I have no idea if/when it was changed last , and the wires , distributer cap and rotor came off my 95 Jeep when I did new on it . I did pull the rattling cat but it wasn't dirty or clogged at all , it made little/no difference , just no more rattle .The truck is far from clean , and I kick the crap out of it , it gets NO mercy . I rev to 3000+ in the short gears easy , do little hwy , but some freeway driving . Drive about 800 miles monthly on 2 tanks (approx 23 gallons , is that right ?, smallest tank maybe)with a little to spare .
My math (no overhead console) ranges from 17-20 mpg's per tank , which I religously clock . I run 32x11.5x15" tires and have changed the speedo gear to match the GPS for correct speed +/-1 mph .
Even the motor knocks a little but has decent power . I want a new engine , but , it's a beater to me , as long as it starts , and it quickly does , I will continue to run it to the ground .
I have no explanation for the good mpg's , I don't get close in my Grand Cherokee with a low K extremely well maintained 5.2/auto , only difference is the 3.73 in the jeep and the slush box .
No BS either , the truck sits right now with 400km's on the tank and 5/8's left and I was doing a side job carrying stone and cement , approx 1000lbs worth for 2-3 days back and forth to work .

Best Dodge I have ever owned for mpg's in fact , my 2003 Quad 4x4 4.7/5spd did good at 17ish(off-road pkg) , but my 2wd 2001 Dakota r/t was a little piggy 11-13 , same as my present 5.2 Jeep . My 2.5l BMW gets 30+ @ 80mph , if I want economy , that's what I drive . 2000 miles with it in 2 yrs , LOL , but a sweet ride

 

But I am partial to the old square body Chevies. I like the look of the dodge, But dont care much for wires and vacuum lines funning all over under the truck to speed sensors and actuators. Seems like a bad idea on a 4wd. Plus I want 4 full doors that open the same direction. Will be a common rial doage and manual transmission. Working a deal to pick up a cummings/5 speed combo with only 125K miles on it.

 

I think you stated further back in this thread that you checked the plenum and it looks good. As far as I'm concerned the ONLY way to truly know is to tear it down. I thought mine was fine and only took it apart to install the Hughes plate I had for a couple months, and sure enough it was blown. I repaired it only 2 years ago using the stock plate. (that was before I found this place).

 

I just pulled a trailer today that weighed right at about 4000 lbs with my stock 1500 with the 318 engine.

started with a full tank - went 108 miles - filled back up and took 12 gal.
do the math and that's a big 9 mpg pulling a fairly heavy load. I'll have to check the mileage when not pulling a bunch of extra weight next (only had the truck a relatively short time and hadn't thought to do this yet for some reason)