High RPM mileage results

[Bertram65]

I have read on here many times about how running 2000RPM or less will yield good mileage results, I have tried this on trips to southern Jersey a couple times with no increase in mileage. I have 4. 10s so for me to run 2000 less I have to run slow but I tried it and noticed no increase in mileage.

This last weekend, some friends and I went snowmobiling at the Mt. Washington resort, we were in two trucks, mine and my buddy's Excursion, as he was leading the way I was following, we ran 80mph most of the way which is 2500RPMs for me, up and back. When we got close, about 20 miles, a storm had moved in and we ran about 50mph, I was in 4wd. Today I finished the tank of fuel with a fast run to NH for an emergency service call. I had close to 400 miles on the tank when I filled up, got 16. 7MPG. This is one of my all time high mileage tanks, and it is winter fuel.

I have always thought the comments about running 2000 rpm and under making a difference in mileage did not match up with my results, this tank really proved it. Most of the tank was run at 2500rpm and the rest was in 4wd with the OD off running in 3rd.

 

[LesStallings]

I don't have enough data to be sure, but initial indications seem to lead me to believe 2,200 RPM is better than 2,000. My truck has 3. 73s and this was observed pulling a trailer empty for 2K miles and loaded for 2K miles.



The available power for the hills and the EGTs seemed to be best at 2,200 RPM also. Much of this is seat of the pants and I need to crunch some numbers and get another 4K miles of data next week.



My truck is completely stock, performance wise.



For what its worth... .....

 

[Alan Reagan]

My experience is that these engines like to turn up and run fast. I got better mileage with my 01 running 4. 10 rear than I do with my 05 running the 3. 73. My 01 would turn about 300 more RPMs than the new one at highway speed. It's hard to say exactly because the ticks on the tach are 125 rpms each. Who thought that up?



I just returned from a 600 mile round trip to Jax. Running with the cruise on 75, I got 18. 8 (calculated). My 01 typically got between 20 and 21 on the same trip. Except for about 50 miles inside the Jax beltway, it was all interstate with no stops.



This one has 3600 on the clock and the mileage running the two lanes at about 60 is running about 19. 5-20. The 01 running the same roads was getting 21-22 at that speed.

 

[Motofreak]

This is interesting have you read the latest TDR? It talks about this. Goes against everything I`ve heard about slowing down for better mileage. Will be following this thread.

 

[GWoody]

MMMMMMMM, I think someone said the pilot injection shuts off at a little over 2000 rpm, might make sense!!!!!!

 

[drewRoberts]

news to me here



I got back saturday from going out to Little Rock, just a nudge over 550 miles there. and made it in one tank with another 80 to spare from the overhead which is a moot point. , however from the 1300 miles I put on it last week I got around 21 miles to the gallon. kept the speed at 70 just about the entire way, thats right at 2300rpm with my 4. 10's

 

[DBond]

This is interesting to me, as I am wondering if the lower ratios of the G56 will hurt mpg.

To get good data, it seems the different RPMs should be compared at the same mph. (shift between OD and 5th or 3rd Auto) Air resistance increases with higher speeds and changes the amount of work the engine has to do.



It doesn't seem like a comparision of the rear end gearing of an 01 and 05 is fair. There are many differences between the 2 years other than gearing, and the 04. 5 - 05 generally being reported as lower mpg than earlier ones.

 

[DPKetchum]

Towing 8600 lbs at 60 I get around 15mpg. At 70 its 12mpg.

 

[Cattletrkr]

just my take on things

I get better mileage at 60mph than I do at 70mph and it's not even close. I drive in too many different conditions to bother running them down here, but it's the same across the board. Lower economy at higher speeds for me. Rickson's 19. 5's did not seem to help, even though I lost about 6% on the tach at the same speed.



My '01 acted exactly the same as the 04. 5 does.

 

[doldenburg]

funny how everybody gets better mileage than me. who's fibin who.

 

[Gary - K7GLD]

HMMmmm - I've used the instant MPG function on my overhead console, and run MPG vs MPH from 55-70 MPH, and found that MPG falls by a good 3 MPG per 5 MPH speed increase - even worse when towing...



I realize many don't trust the overhead console for actual MPG, but it IS a good tool for tests like this!

 

[Alan Reagan]

I'm not fibbing anyone. At highway speed I got 18. 8 on my last trip. My point was, that the mileage was less than I got on my 01 with a 4. 10 rear that would have been turning more RPMs than my truck with 3. 73. If I slow down, I get better mileage. There's no doubt about that. I had read somewhere that the mileage drop on these trucks is about . 1 mpg for every mph over 55. That's about what I've seen. Trucks have a lot of wind resistance so I think it's more a function of resistance than engine speed.

 

[tae73]

One thing also to figure in that no says is the terrain of the area they live in. Flat land will get you better mileage, than semi hilly, and hilly will get you better mileage than mountains. It takes more power/boost to get you up hill than running on flat land. Also, you cant compare mileage with someone that lives in different parts of the country. Different fuel grades and weather, and if its cold some of us let them warm up for 5 minutes or so that kills mileage also. I dont worry to much about mileage, I know that it gets better than my old chevy 6. 0 gasser and has bunch more power.

 

[Alan Reagan]

Terrain down in central to south Georgia is just long rolling hills. South Georgia into Florida is flat. Yep. That helps with mileage. Where I've gotten my best mileage with any of the three TDs I've owned was running coastal Georgia/Florida. At sea level, I've seen the best mileage ever.

 

[Udaloy]

MMMMMMMM, I think someone said the pilot injection shuts off at a little over 2000 rpm, might make sense!!!!!!

Can someone clear this one up for me? I've never heard of the pilot injection stopping, but I thought I heard that the third injection event would stop if you were cruising, even if you're above 2000 rpm. Is that true, or is there always a third event above 2000 rpm?

 

[XJSuperman]

I typically run between 1900-2300 RPM. In city, highway... doesn't matter. I don't try to kill the truck but I far from baby it.



All that said I get 17+ city and 21+ hwy with the last 3 tanks being 50/50 and I ran 19. 3, 19. 5, and 19. 2. This is all empty with EZ on 4, AFE intake and 4" exhaust.



Seems to me running it at the higher RPM is NOT hurting a thing.

 

[RMalone]

my 04. 5 w/30k mi. gets about 16. 5 to 17. 5mpg hand calced, this is on mixed city,hwy and freeway driving. My truck does its best 18. 5 to 19. 5 on hwy driving (45 to 55 mph). On the freeway I definately see a decrease as speed/rpm goes up. Speaking of wind resistence I have seen a pretty substantial difference between going 70 into a 15-20 mph wind versus having the same wind on my tail prolly 2mph. As mentioned terrain makes a big difference also. Unless two trucks are on a convoy its real tough to compare mileage and really learn anything. I dont tow more than an 18ft boat, hell I dont even need a diesel, I just LOVE the way those babies sound :-laf .

 

[LDobie]

Speed certainly has a huge factor in this whole scheme in that Aero drag increases exponentially above about 60mph. It seems that all things being constant, if you were turning less RPM (less times per minute that fuel is being injected), you should use less fuel. There are several other huge variables, the biggest being Aero and if you are pulling more RPM, you have more HP available, so it doesn't have to work as hard, just a little increase in the throttle and you're good.



While I don't have a CTD yet, my dakota is a good benchmark for this whole thing. This truck sits a bit lower than a 3/4 Ton, and is extremely aero sensitive. If there is any head wind at all on an interstate, and I run around 72mph with no drafting help, I'm around 15 mpg. Under those same conditions, if I can get good drafting help, I can pickup nearly 4-5mpg. Even by myself, I can feel a big difference running 70, compared to 75. This truck runs best on back roads at 60-65 mph, where I can see nearly 20mpg.



In conclusion, I was concerned about turning too many RPM if I buy a late edition '05 or early '06, but I guess from what you guys are seeing, it doesn't make a huge difference if any at all. Aero is the biggest thing then, with Mountains of course :-laf In the effort to save fuel and $$$, you all should pay attention to finding "drafting partners", not tailgating, just someone to break the wind, it makes a big difference.

 

[Kirwin]

Miliage vs speed

The laws of physics say that as speed doubles resistance goes up by a factor of 4. So you are using more energy at a higher speed to maintain the same load at the higher speed. Now to put this into real world numbers the difference between 65 and 75 MPH fuel mileage is dependent on a lot of different things that are not part of the physics solution. Our trucks are definitely more EFFICIENT at a certain RPM (reference TDR issues on specific brake horsepower VS fuel consumption) which in high gear corresponds to a certain speed. The "other factors" IE how you drive, auto vs manual, how you accelerate up the hills, do you use cruise control, or use your foot to anticipate hill climbs, have as much to do with how much real world MPG change you see between 65 and 75 MPH. My personal experience is that I can get about 1. 5 MPG more pulling my travel trailer if I feed manually than on cruise control even though I end up going faster a lot of the time if I use my foot since I can pick up a little speed going down the hill and then add more fuel smoothly as I start up the next hill instead of cruise control pouring it on as you start up the hill. All the above IMHO. Ken Irwin

 

[RMalone]

Are you really making more horsepower at a higher-vs-lower rmp while traveling a constant speed? It seems like it would take a certain amount of horsepower to move the truck at a certain speed irregardless of rpm? Now the amount of fuel needed to make that horsepower might be different for varied rmp?