2nd Gen Non-Engine/Transmission 55mph best for gas mileage....with cummins too?

[TLanier]

howdy,



always read how driving 55 mph is the optimal speed for gas mileage, and that 65mph burns 10% more, 75mph 25% more than that. does that also apply with a cummins, with all that torque?



i mean, at 55mph, im well below the magic fuel efficient 1800rpm number. i hit that with my 31' tires at about 62mph. so i set the cruise for 62mph and get 20mpg. anyone think that driving under the 1800rpm number at 55mph would get better mileage? (not that i could stand to go any slower!).

 

[JDougherty]

i would have to say that i found the less boost i am producing the better the mileage. seems to me that more boost means more effort needed by the motor.

 

[SHobbs]

Setting the cruise at 62 works for me, keeps me at around 22 1/2mpg. There have been many threads on this issue and someone said that anything above 65 it will drop. It's true with my truck, 65-70 isn't too bad and above that it's all downhill from there.

 

[keimmmo]

I often drive on roads where driving over 60 IS NOT an option!!! My 01. 5 has "sweet spots" at 48 and 58 mph. The economy drops very slightly from 58 up to 62. From there on up it drops quite sharply!



Steve Keim

 

[JasonBrown]

It is not reasonable to pick a magic speed and apply to everyone, too many variables, manual trans. /auto trans, tire size, terrain, load, etc...

 

[KennethS]

I wanted to see If I could get good fuel mileage and did

I have a Class C Motor Home on a one ton Dodge Chassie powered by a Cummings. I knew what my fuel mileage was at speeds 65 to 70 were andI was only getting 14. I knew I could get better If I kept the speed down. This summer my wife and I were drivine down through Miss. and was getting on the Natchez Trace Parkway and was going to stay on It for 300 miles. I just fill up with fuel and the speed limit was 50 to 55. Boy what a chance to see how good fuel mileage I could get. I tried to stay at 50 sometimes going up to 55 and back down to 50. I pampered the Cummings as much as I coud. There was no traffic to speak of also. I wanted to get 20 but did not the best I got was 17. 6. For a Class C Motor Home 25 footer I think that pretty good I think. I have not got that since that trip. I was reading that Cruise control cuts your mileage 2 miles per gallon?Now when I run 65 about 14 Is the best I get and would Like to do better?Maybe leave wife home you think?

 

[The patriot]

Unless I use the cruise control, my highway mpg's sux.

At between 70-80mph I get about 15 MPG's.

If I can keep it at about 60 I get 21+.

Eric

 

[Fishin Guide]

I got the best milage of my the year when I drove to Montana this summer.



I got 23. 3mpg and that was all over or at 75MPH. Cruise was used all the way and the comp was on 1x3.



Dave

 

[Clinton]

I've been driving strictly by the tachometer here lately. On the highway I keep it right at 2000 rpm, maybe a little less, which is a bit below 70 mph. I can squeeze 20 mpg out of it at that rate. With my 4. 10 axles thats about all I can expect. I agree that when I'm seeing more boost in hill country my mileage gets worse. I used to drive faster; up in the eighties somewhere with rpm around 2200 and I'd be lucky to see 17 mpg. So I suppose my extrapolated answer is yes, slowing down will increase efficiency. Now, about the 55 mph... I can't say what the point of diminishing returns for my rig would be. I can't ever seem to go a whole tank at that rate on the interstate. If I'm travelling in that ballpark its always on slower roads where my boost is up and down.

 

[JFaughn]

From what I've experanced over the yrs. is that RPM is first , for Cummins its 1650-1750 and thats about 60-70mph [with my truck] and the after 50mph is about the wind and for the Cummins the wind seems to take affect after the sweat spot of 1750 rpm

 

[robertyoke]

howdy,



always read how driving 55 mph is the optimal speed for gas mileage, and that 65mph burns 10% more, 75mph 25% more than that. does that also apply with a cummins, with all that torque?



i mean, at 55mph, im well below the magic fuel efficient 1800rpm number. i hit that with my 31' tires at about 62mph. so i set the cruise for 62mph and get 20mpg. anyone think that driving under the 1800rpm number at 55mph would get better mileage? (not that i could stand to go any slower!).

55 mph! on I 25 or I 70 you would be a speed bump! even 62 is to slow! go 65 so the semi's dont have to pass you.

the number 1 cause of auto accidents is not moving with the flow of traffic, to fast in most cases, but to slow will cause others to go around, impeding traffic flow. you would be a hazard!

Is it worth 1 mpg??? :-{}

 

[TLanier]

Im laughing at your response robertyoke!!!! if you only knew me, and knew what a restraint it takes me to drive that slow!!!! i drove my wife's honda accord V6 100 mph for a couple hours over two lane roads in the middle of nowhere (wyoming-southdakota) to go and pick up the truck when i bought it. i loooooove to drive fast and be consistent, and i HATE driving slow.



When i drive 70-75, i get 17 stinking mpg. when i drive 62, i get 20. 5 mpg. it just burns me up when i see guys with 4:10 duallys saying they get 22-23!!!



honestly, if i were not so broke, and diesel didnt cost so much more than gas right now, id be driving 80 in the truck!

 

[The patriot]

My UTE bumper seems to have hurt my MPG's also, but I can live with it.

Eric

 

[rivercat]

Anything to the: Switch everything to amsoil and gain X miles per gallon cause its sooo slick you can coast for miles...
statment

 

[DKarvwnaris]

Anything to the: Switch everything to amsoil and gain X miles per gallon cause its sooo slick you can coast for miles...

statment

Oh boy, here we go, more snake oil propaganda. Even if the physics defying Amsoil was capable of the orgasmic levels of peformance, the cost to buy that pyramid scheme stuff will stifle out any fuel savings by itself. Anything that sounds that close to "AMWAY OIL" makes my skin crawl. viscosity is viscosity, there's no magical way to change that.



If you really want to get better fuel mileage turn the fuel down, keep the black rolling clouds from forming at every stop light and don't pass everything just because the "truck wants to". Only other solution is pulling the 5. 9 engine out and putting a 4bt 3. 9 in its place. That will get you in excess of 5 mpg easily.

When I get the self control to do just some of these things myself, I know I'll be up to 18 MPG again. Til then, I am perfectly happy with the 16 to 17 mpg I get on average empty.

 

[WestTN]

Aerodynamics is the major factor affecting fuel mileage. The faster you go the more you burn. Over a certain strip of flat road I can see 32 mpg at 35 mph in sixth gear. At 45 it is 26. at 55 it is 23 or 24. at 65 it is 20 to 21.

 

[SBurton]

I don't whats going on here, my best fuel mileage was 16 empty, 04. 5 with CARB emission controls. usually 12 to 15. I think no one wants to tell the truth.

 

[DKarvwnaris]

I don't whats going on here, my best fuel mileage was 16 empty, 04. 5 with CARB CARB is reason enough, not to mention the traffic I am sure you get to park in daily emission controls. usually 12 to 15. I think no one wants to tell the truth.

I am pretty sure I posted 16 to 17 empty. Loaded it is in the lower teens at best. There is NO ONE on here getting over 20 mpg with any year dodge 4x4 truck, this is a reality, nothing else. I could possibly see it with a 2wd on a downhill grade for the duration of a fuel tank's capacity. (despite whatever that trinket compass and fuel mileage screen tells you, it is not reliable for actual mileage and fuel consumed). It is impossible to rely on a single tank fill up to check mileage of a vehicle. Different fuel stations will click their pumps off at different levels in your fuel filler neck, not to mention a nearly plugged filter in the gas stations pump lines will effect flow rate if someone is trying get a measured amount out between clicks)

I have to admit that I have never owned a full size truck of any type that can achieve the mpg my dodge can. I have 3. 55 gears and 285 tires on it. That is something in itself without having to boast unrealistic #'s that I see on this site all the time.

 

[Nate]

I don't think RPM has a huge effect... I think it's boost really. Figure your boost guage is showing you how hard your engine is working. I read somewhere it's 1psi boost = 10hp... does that make any sense??

 

[DKarvwnaris]

I don't think RPM has a huge effect... I think it's boost really. Figure your boost guage is showing you how hard your engine is working. I read somewhere it's 1psi boost = 10hp... does that make any sense??

Not sure on the PSI verses HP output, but I agree that the more boost, the lower the MPG. Reason being is the more boost you're pushing, means the higher amount fuel you are pumping into the engine. Ever notice the boost goes up shortly after you push the accelerator down further? More fuel, more boost