Engine/Transmission (1998.5 - 2002) Poor MPG revisited

[onestackdram]

Ok I have reported before that the wifes '02 has been getting extremely poor fuel economy. I have gone through the steps. I have checked both MAP and IAT sensors for cleanliness. Have changed fuel filters, and check fuel pressures. All are in perfect order. I have accounted for the larger sized tires that are on it. I completely ignore the overhead console as I have found it to be completely inaccurate. Before I was almost ready to chock it up to the fact that it normally only drives in the city for about 2. 5 miles one way with the occasional errand run around our little town. But I have driven this thing for 3 FULL tanks up and down the highways. The first tank I drove it like I was a half hour late for everything (thinking that maybe she babied it too much). That method resulted in only 15. 2 MPG. Then on the second tank I babied the heck out of it driving like I had 2 hours to kill no matter what. That resulted in 16. 1. Then on this last tank I gave it a very happy medium, not accelerating to much but not being a weenie with it. And that resulted in the best of the bunch at 16. 75. On all three tanks the highway speeds never exceeded more than 75 and never lower than 65. Usually right at 70 mph. I am out of ideas guys, is there something wrong with this truck, or is that 20 + MPG just a myth? I am beginning to think that the guys reporting such numbers are just spouting what they clanced up at the "current" MPG on their overhead showed while they were going down hill with a tail wind. I have checked all codes both by the good ole on/off on/off on with the key method, and then with an OBD II scanner. They only thing that is coming up is that it is over boosting. I know why it does that. Because I threw that HX-35 on their to get rid of that dog HY and it is not wastegated yet. But the poor MPG where here long before I did that. Let me know what I am doing wrong fella's.



TIA



Russell

 

[James2000]

I've never gotten over 16 mpg, and I hardly ever tow. I do go up and down a canyon almost every day with an elevation drop/gain of 3000'. Hardly ever on highway, always city or mtn. roads. Don't know if this helps? Just the way it is! James

 

[Texas Diesel]

Same here, my 01 gets 15-17, her 98 gets 22, thanks EPA.

 

[HeavyHauler]

I think you have to learn how to drive it...

Well I was having the same problem with my 2001 dually for a long time and then I discovered that these things are really sensitive when it comes to fuel mileage.



Driving at 70 MPH will kill your fuel mileage, it did mine, and I'm sure that's what is happening with yours. Just for kicks, on the way back from Woodstock, GA, about 450 miles, I averaged 19. 3 MPG in my truck. But, I did not break 60 MPH the whole way. I was used to getting in the low 16's. Well that showed me the light and now I drive slower than a little ole lady going to church on Sunday. I always average in the mid 18's and I drive a lot in town. Constant speed is the key to the mileage and you gotta keep it under 65.



This is what I have found, I'm sure someone will get on here and say that they average 21 MPG driving 80 MPH all day long. Yeah right.



Take an hour or two trip on the interstate somewhere at 60 MPH (I use the cruise all the time) and figure your mileage. Let us know.

 

[Mundgyver]

Ditto on what HeavyHauler said,



I'm getting 22. 78 mpg empty after putting on a FASS unit, but anything over 65mph and you kill the mileage. With 7,000 lbs of trailer at 65 mph steady from Provo, Utah to Portland, Oregon I will get 18. 5 mpg. If I move up to 70 my mileage drops like a rock to the bottom of a lake.

 

[Sticks]

Seems a bit low, but now I am right there with you. Before I had the LP changed out, and started having all these damn 0216 codes, I was getting high 16's low 17's in the city, and 19 - 20 highway and mountain trips. Now I am lucky to get in the high 15's, and the highway trips barely break 16.

 

[243]

Same as above, my 01 gets 15. 5-16. 5 mpg around town (lots of fwy) but I drive 70+ constantly. On my last trip out of Houston, I drove 60 with a throttle lock instead of the cruise and got 22. 5 mpg.

 

[GIT-R-DONE]

Ok, first , what gears do you have? If you have the 4. 10 and are running 75 mph, this will kill the mileage. If you have the 3. 55's then 70 is a good cruise speed. My best mileage has been 21. 6, and that was at 55 mph on a 2 lane highway in rolling hills. My worst mileage has been 12, and that was towing @ 8000 lb trailer thru West Virginia. One other thing is to try and get your fuel from a different location as I have found that not all fueling stations were created equal. I have found a small fueling station here that I get better mileage from, so maybe try that and see if it makes a difference. We have a local utility company that, every fall, goes out and gets fuel from different suppliers and has it tested. I watch to see where there trucks fuel up and I go there too as I know where they are buying the fuel, must have been the best of the test. One other thing I always wonder about is , how much of a diffeence does the auto transmission gain/lose over the 5/6 speed. Do you lose any HP thru the auto? Just my . 02 Don

 

[TboneMan]

You mentioned oversized tires. What size are they?



The power needed to start and keep bigger tire rotating is greater than that needed for smaller tires. Also you have greater surface area (read more friction) touching the pavement. This will drop your milage.

 

[Mtngoat]

Russell-



For what its worth, different truck and all. . Driving it 70-75, I got high 16s and low 17s. Driving at 65 I got 20. 1. . Thats with no a/c on, windows rolled up and sitting low in the seat!!



Robin

 

[RowJ]

One Stack

I'm with you! Best I can do local (60% Highway) is 16 - 16. 5 mpg. On Hwy trips can get 18 mpg @ 60, 17 mpg @ 70 mph, in the 16 teens at 75 to 80. Picked up none of the advertised mileage gains with my mods!!!!

This thing drives so well that most of the time I don't care... but there was that 19. 2 MPG I got once when I first bgt it (12,000 miles & stock) and was babying it. i miss that.

Many threads say your right foot is biggest factor but my hwy tests were serious efforts to get the max I could. And I never could match stock????

 

[Marco]

Tire size

Taller tires without speed correction is a big mileage killer.



Taller tires kill the mileage in two different ways.



First of all you don't read the correct distance travelled on the ODO. Sure one can GUESS how much the ODO is off but that's all what it is a guess!.



Second, when you read the speed you're doing with the taller tires your actaully (much) faster than the reading.



Nothing new?



Well, I have 33" tires on my truck. Have had them for the last 3 years. My mileage always sucked big time! A couple of weeks ago I finally decided I HAD to know. I went for a test drive with a GPS on the dash. WOW! I did not know how much faster then the speedo I was going in reality!



So I corrected the speed for the taller tires.



The top speed of the Cruise control was reached before the correction at about 2400 RPM, after the correction the same speed is reached at about 2100 Rpm!!!!!!!!!!!!!



In other words, I've "gained" 2. 8MPG since I've corrected the speedo!!!!!!



'Nough said?



Marco

 

[jandr]

about right!

I was just starting to get around 16. 5 to 17. 5 at about 70,000mi. Then I took it to Dodge for a transmission module(extended warranty) and unknown to me ahead of time they did a computer flash on it which updated the ECM(I guess). After that my mpg went down by about 10% to average 15. 5 --- I just installed DPP's 4" exhaust and have run 2 tanks through. First was 17. 3 next was 17. 0 My driving does vary but is usually about 20% town(shifting) 80% hiway(70 to 80 mph). The best that was ever gotten was 25 mpg --all hiway, driven by my wife on a trip following an old motorhome going only around 50 mph. When I spend a lot of time just around town, I get REALLY crappy mileage. Never checked accurately but I swear it's only around 12 mpg. I think your about normal. The 12 valve do much better from what I have heard and I think alot of guys only look at the computer and don't know how to do the math. The good news is I have a friend with an '03 and I get better than him!!!

 

[mhenon]

Milage

My rig has a tonoue cover on it, which is worth another 10%, and gets over 24 mpg on the highway with the cruise set at 65. This isn't a guesstimate as I have added up the gallons used against miles traveled on several 1000 mile+ trips.

Also, being a 2wd rig and lower to the ground it's going to do better then most 4wd trucks.

I believe it was broke in perfectly too... . hauled a trailer through Mexico last year and put on about 15,000 miles in the process.

At 30,000 miles I switched over to a synthetic 5W/40 oil and I'm sure that doesn't hurt anything.

Keep the tire pressure up on the high side while your at it. A low tire or two is going to drag your mileage down (and be unsafe).

These rigs do get good mileage. I've check my speed and miles traveled against a GPS unit and the truck is right on. So far the best RPM/ MPH for economy is at 1750 rpm and 62. 5 mph. I'm not going any slower but it might do a little better under that... you'ed just never get where your going.



Mike

 

[JR2]

Your mileage sound about right to me. I get 15-17 on the highway and 10-15 in town. Most of my poor mileage (10-12) comes in the winter when we have crappy fuel and I pull my snowmachines around. That and I leave the truck on high ilde to warm it up.

I have kept track of every tank I have put in the truck since it was new and after two years I averaged the numbers in Excel and it came it 15 mpg over all. I am happy as the truck is quite a bit more fun to drive than my old ford 1/2 ton gasser that got 8mpg all the time.



Like others have said, there are lots of variables. Put your tire pressure to the maximum, drive at 60 mph, leave the AC off, coast down hills and you will get 20 mpg. Drive like most of us do and you get 15-17.





JR2

 

[MMiller]

Tire selection has killed my milage too. I checked mine alot,( dividing miles by gallons, no over head console in my baby!) and could consistantly get 19-20, and up to 24 on LONG trips. After adding the 33X12. 5's my milage went down to around 17. I think it is the mud tread and the 12. 5 width that is killing my milage, because the speedo is correct mile marker to mile marker, as is the odometer. The "33s" are maybe an inch taller than the stock tires that were on the truck.



Also the mud tires are load range d on my truck, the tires were E's with steel sidewalls. I think this adds a lot of rolling resistance.



Just my $. 02 on my old first gen.



Michael

 

[RowJ]

Michael

Don't see how mileage from marker to marker can be the same on a 1" taller tire. Don't have the energy, this late it the day, to do the math on circumferences but seems as though it would be significant over a mile (maybe 5-6%).

Any math majors out there?

 

[Marco]

Mile Marker

MMiller,

I've tried the mile marker thing often. Yup, that way the speedo looks close to what it should be. With the accuracy I was able to get ( Timing watch, constant speed... ) I too thought the speedo was correct. When I checked with the GPS... ohhhh no!



My tires are the same size like yours (Goodrich). My truck came with the 245's Michelin tires. I think the speedo was calibrated for those tires. To get an accurate speedo reading I had to calibrate the tire size 2. 25" taller!



A hugh difference!



Marco

 

[onestackdram]

well the stock tires on this truck like everyone elses were 245's and when we bought the truck 8 mo ago it has 285's on it now. And by my math that made everything off 5%. Meaning that 100 miles was actually 105 so on and so on. The gears are 3:54's so it has the good highway gears.



Russell

 

[Jetson]

My 265 tires need a correction of . 0463. 285's will be more. You can go to a tire website that shows the height of the different size tires and calculate the difference, plus as others have said, the taller tires raise the truck causing more wind resistance at speed.