Engine/Transmission (1998.5 - 2002) Poor MPG revisited

[Jetson]

Michelin shows the 245/75/16E to have 681 revolutions per mile.

The 265/75/16E has 652 rev. per mile. x 4. 4% = 681

The 285/75/16D (no E listed) has 634 rev. per mile. x 7. 4% = 681.

You should multiply your miles traveled by 7. 4% before calculating your mpg.

 

[LarryG]

My '02 4x4 auto is completely stock and sports a 4:10 rear end. The best mileage I got was a trip to Nova Scotia and PEI (best mileage was on the ferry across!) On that trip I averaged 23. 46 mpg, but it was lightly loaded - suitcases and a cooler. That included the highway mileage up and back, the rest was tourist speeds - 35 to 50 mph. Around town, I get 18 to 19 and it suffers some during the cold weather. With the 4:10, it definitely does not like 70 mph so I have adjusted my driving habits - I leave home a little earlier! I'll admit that I keep the overhead console on the mpg mode and I find myself looking at it a lot. I thought that you could tell my the sound of the engine how you were doing on mileage, but it surprizes you sometimes. I take it easy on acceleration and grades. I don't use the speed control at all because I can do better by anticipating the hills and letting it gain speed on the down grades. I'm happy, the last 3/4 ton 4x4 gasser I owned was during the energy crisis in the mid 70's and it got 11 mpg - ouch!

 

[MMiller]

I don't have access to GPS and the milemarkers is what I have to use. I haven't been pulled over for speeding in my truck for several years, so I know the speedo has to be dangerously close, because I always push the speed limit. I haven't had any warnings when I was doing the correct speed. This is how I go, right or wrong. The "33"s really only measure about 32" tall and they are MAYBE an inch taller than stock. It has been so long since I have had stock tires on the truck that MAYBE the speedo was a little fast before, I can't remember.



I guess the point I was trying to make was my mileage went down with the tread design, soft sidewall, and the width, all making more rolling resistance, less aerodynamics, taking more power to run down the road. I could pump the tires up hard but I drive a first gen and you know all about the ride. Also I like to wear the whole tread section not just the center. Also I have a terrible time getting it to hook to the street as it is. If I ran at 50 psi all the time I couldn't get off the stop lights without spinning the tires.



I know the mile marker routine isn't perfect but it works for me, and lets me know if anything is different with the truck.



I also don't know much about GPS. The company I work for sell GPS systems for the ag equipment I work on. I have read there are different levels of accuracy, depending on the amount of satellites and the level of GPS you are using. Along with if you are using a selected ground position to know with in mm of where you are at. Does this apply to your system? Our level of accuracies go from several meters to 1mm accuracy, depending if you use the general GPS or if you pay for the higher levels of accuracy. Is this making sense? How does yours work? Can you be sure it is totally accurate? Are the mile markers off alot? I understand that the satellites are somewhat jammed with varying accuracy, this is why we use a know position on the earth that the GPS unit uses to adjust for the variables. Is this how yours works?



Not trying to shoot holes in your setup, or way of looking at it, just trying to learn something. I am not very knowledgeable about GPS. Just what I have picked up at work.



Sorry for the long post and I apologize for my ineptness in the GPS area. I hope I got my thoughts out in away that is understandable.



Michael

 

[new2dodge]

I get 18-20 mpg. mostly city& urban hwy driving. mines mostly stock except for a power puck. A friend of mine has an 02 powder( yes powder stroke) he only gets 13-15 on a good day.

 

[RobertMiller1]

gear driven

so aren't these speedo's gear driven? Seems Chrysler has made many different gears over the years for the 727 torqueflite transmissions our current trannies are based upon.



Wonder if we can change little plastic gears for proper speedometer calibration with new tire height?



There are several tire/final drive calculators on the web.



Seems you could plug in the new tire height and calculate the change in final drive ratio. You would then be able to select the appropriate speedometer gear to match the calculated final drive ratio.



I remember my 1974 Cuda had a 3:40 rear as an example. So, if my new calculated final drive ratio was 3. 40:1 then I would use a plastic speedo gear for a torquflite from a 1974 Cuda with 3:40 rear gears.

 

[Mundgyver]

Speedometer reading are taken from a electronic sensor that looks at a ring gear intrupter in the back axle for a frequency reading which equivates to speed.

 

[RobertMiller1]

wonderful

:--)

figures.

 

[Texas Diesel]

Getting back to poor mileage, the only question I have is why does my 12v get 22 MPG and my 24V get 18 MPG when driven the same roads & speeds (to work and back) if MPH is the only factor? No doubt that slower driving halps MPG, but two trucks driven identically and getting 4 MPG difference. Could the w4d extra weight be it? Both are sticks and 3. 55's. It seems the MPG goes down every year, I suspect EPA rules are the problem.

 

[RowJ]

285's not off by much

I drove the company delivery truck yesterday (Izusu Box Truck) on the interstate between two well known highway signs -showed 30. 2 miles on odometer. Last night I drove my CTD w/ 285's over same course - showed 29. 8 miles. Assuming factory Izusu speedometer is accurate my 285's are only off . 3 miles in 30. When I put 285's on my 99 dodge, my speedometer was off 8%. How can my 2002 be off only 1%? ?? I'm confused.

 

[DavidPope]

just got an 01. 5



1st tank - round town & 10% freeway - 17. 2



2nd tank - 80% freeway (70-74MPH - CC)- 18. 2



going to be getting bigger tires soon... will let you know.



oh, and it is a 4x4 with the 3. 55 LSD



I was too hoping to get over 20MPH when I upgraded from my 12 valve. That sucker got 16. 5 MPG with my foot in it or when grandma was drivin, on the freeways or on in town, uphill or downhill





And I agree... the overhead cmptr is worthless... do the math

 

[Hohn]

Re: 285's not off by much

Originally posted by RowJ

I drove the company delivery truck yesterday (Izusu Box Truck) on the interstate between two well known highway signs -showed 30. 2 miles on odometer. Last night I drove my CTD w/ 285's over same course - showed 29. 8 miles. Assuming factory Izusu speedometer is accurate my 285's are only off . 3 miles in 30. When I put 285's on my 99 dodge, my speedometer was off 8%. How can my 2002 be off only 1%? ?? I'm confused.

You can't compare distance from one vehicle's speedo to another vehicle's speedo and expect it to be accurate. You have to have consistency, so either use only your Dodge speedo (swapping tire sizes) or something independent like GPS or mile markers.



I believe the most reliable comparison to be revs/mile published by each tire maker. If you go from a 655 revs/mi tire to a 624 rev/mi tire, you're going to see a difference of about 4%-5%. So, MATHETMATICALLY, you already lost 5% of your MPG.

But larger tires also impact fuel economy with more rolling resistance, and more weight. Moreover, the increased ride height of the vehicle will ALSO increase the wind drag, thus costing you even MORE mpg.



The "road hp" at speed varies GREATLY from one truck configuration to another. That's why a lifted 4x4 dually with an automatic and 315 75r16 aggressive tires gets really bad mpg (13-14 max) while a 4x2 SRW 6 speed with 245 75r16 hwy tires can usually get 25+ without a sweat.



My neighbor's '01 ETH gets good mileage regularly. He's all stock, and gets 24-26 on the hwy @65mph if the wind is calm. He runs Rotella.



On the other hand, I usually get 15. 5-16. 3 around town, and 19-21 on the hwy. And I run "synthetic".



The differences? I have a 4x4, he has a 4x2. I have 20k miles, he has 186K miles (yes, on an '01). I have 265 Michelins that came stock, he has the 245 michelins (replaced w/same model every time). i run 70-75mph on the interstate-- he runs 65.



The only time to be REALLY concerned is when you have a HUGE mpg difference compared to someone else's truck that is EXACTLY the same as yours, or very close. Since its pretty rare to find someone's truck even with the same options, it's usually an apples to oranges comparison.



I would recommend you be more concerned with optimizing YOUR mpg, not so much with what everyone else is getting. I hope this helps a little. Remember-- it's ALL relative when it comes to mpg. i dont consider teens bad mpg for a 7k pound 4x4.





Justin

 

[DavidPope]

oh and 100% stock except a K&N box filter.



What happens to the milage when you guys put that Big Ass paper airfilter everyone seems to have on here?



I think i wanna do that

 

[Hohn]

The big air filter will not affect your MPG in any way unless there's something seriously wrong with your existing setup. In oue diesels, more airflow will lower EGT a smidgeon, but do nothing for mpg unless you have a SERIOUS air restriction.



justin

 

[mhenon]

Best MPG

There is a thread on here somewhere about air resistance on our Rams. Some University project I think. Their study showed a 10% decrease in air resistance with a cover (tonou) on the bed.

I noticed an increase in mileage as soon as I had my bed cover installed. Mileage went from about 22mpg on the highway to 24+.

That pretty much confirms the study report. I think I figured the tonou cover would pay for itself in something like 150,000 miles (thats what I told my wife anyway). It all depends on what you pay for the cover as opposed to the increase in mileage.

A camper shell didn't do near as well as a cover. The best mileage was with the tailgate down and a modified shell that went from the back of the cab to the end of the lowered tailgate. Wind resistance was lower by 14 or 15% with this set-up.



Mike

 

[Mundgyver]

I would love to have that sloped cover on the back of my rig that is shown in that report. A 30% reduction in drag is a large chunk of fuel improvement. Anybody know if someone makes a cove like that.

 

[geusterman]

Allow me to make some comments on mpg. I was disappointed with my 02 (no front disconnect) making only 14mpg from day one. Ricksons gave no improvement. Gear Vendor no improvement. Recently let Piers clean the MAP/IAT EVEN THOUGH THEY LOOKED CLEAN and checked for boost leak. Now at 18 mpg and when I put the EZ back on should bump up one or so MPG more. Not bad. At 18K now. Should ultimately hit 20 mpg or so on the highway as it breaks in. Way it should be. Check with them on what they use for cleaning the sensors. geusterman

 

[Jeremiah]

The winnah!

Guys, anybody who lies to a fellow TDRer ought to be bored for the hollow horn. I don't know what that means but I've heard it all my life and it doesn't sound like fun. Having said that, my '03 3500 SWR w/6-speed 3. 73 CALCULATED mileage at 30,000 miles ranges from 24. 4 with a tailwind (also 1850 rpm, 62 mph) to 19-something with a headwind (also 2200 rpm, 75 mph).



I routinely drive more than 700 miles on a tank of fuel and if that doesn't come out to 20 mpg or better you can bore me for the hollow horn.



Power settings are the key, along with tires to 50 lbs, clean air filter and filling the fuel tank to the same level every time. After that comes load, terrain, traffic conditions, vehicle and driver differences, and there's no telling about those kinds of things because they're all different.



Otherwise, if you're out on the highway forget how fast you're going unless you want to get somewhere in a hurry. Look at the tach (that's what it's there for, along with telling you when to shift, etc. ) and figger out where in the power band you want to be. If you don't know what a power band is you're driving the right truck but the wrong engine.



But now that you've got your truck, hey, have fun with it. Things could be a lot worse - you could be driving a Ford!



BTW, while I'm jackin' my jaws, here's how to have a little fun: next time you see someone pull up in a new PowerStroke, walk up and ask the driver, "Say, feller, didn't the dealer have any Dodge Cummins available when you bought that Ford?"