Most fuel-efficient speed / best fuel economy?

[Free Bird-SKO]

I get 13 to 14.5 mpg at 57 mph with my 03 fs 65. Now when i drop the speed to 54-53 mph usually get around 15.5 mpg.

My 6 window bus is getting the same mileage but with an older rotary pump and AT545. Since you have a manual transmission I'm surprised you are not getting better fuel mileage. What rpm are you cranking at 57 mph?

 

[cowlitzcoach]

Because most school buses were designed and built transport kids to/from school they generally are not the best when it comes to going highway speeds. The vast majority of all school buses spend 95%+ of their service life at speeds less than 35 MPH. If the bus rarely, if ever, goes over 35 MPH there is no reason to have gearing to go 75 MPH.


The first bus I drove on a route was geared to go 47 MPH. It would go 47 MPH up just about any hill in high gear. On ski runs it would shift down to 4th gear on the last steep parts up to the top of the hill.



The second bus I drove on a route was geared to go 57 MPH. It would go 57 MPH up most hills in high gear but would require 4th on some hills. On ski runs it would need 3rd gear for the last steep parts up to the top of the hill.



If both buses left at the same time they would get to the top of the hill within a few minutes of each other.



Both buses had IHC SV-345 gas V-8's and 5-speeds. Both got about the same fuel mileage.



Fast forward twenty years. Our DT466 210 HP buses were geared to a top speed of 62 MPH. We had two trip buses that had 3208T's 250 HP with a top speed of 75 MPH. On group moves the DT466 buses would get to the top of the hill before the 3208's. Most of the time the DT's got 1-2 MPG better than the Cats with the Cats in the 5-8 MPG range.



Fast forward another ten years. Our 6BT 220 HP buses with MT643's were geared for 70 MPH. Most got 8-10 MPG.


I think that if you are getting anything better than 8 MPG you should be happy.

 

[cadillackid]

The other elephants in the room on mileages is wind ( aerodynamic) resistance , clutch or air fans ,and auxiliaries being driven by the engines.
Sometimes the sweet spot falls in the range of aero efficiency. Sometimes it is above or below the aero efficiency “sweet spot “. Think about it this way. As you go faster the harder it is to move the frontal area of the bus through the air. Air is gas but behaves like a liquid. So in the same respects closing the large negative area behind the bus will help efficiency.

Parasitic draws on the engine are also killers to fuel mileage. Is your air compressor running to compensate for leaks ?
Is the alternator working overtime to charge house and bus batteries?
Power steering an efficient pump or jus an old keep it over boosted pump.

Clutch fans. They are the best and extremely reliable. But hey SUCK fuel mileage down are hard on water pump /mounting bearings due to weight and load the generate. Also need to be kept in balance
Is your cooling system in good working order or is your clutch fan working over time.
Air engagement fans air much more efficient when not engaged because they free wheel truer. But the suck fuel when engaged.
Look at your frontal area close there is a lot to gain in moving air efficiently in and out of the engine compartment to keep the clutch fan from engaging.

I use an Electric fan clutch... just like air but you dont need air to run it..



they are hard on the belt because of the inertia of the fan blade when they start up. you often hear a "screech-Wooaaa" with them.. that screech is the belt...



RE busses are the worst about self-cooling.. their fans run a lot more than FE or CE style.



Tires.. be sure to properly inflate tires.. not only can it be safety related but low tires will affect MPG's..

 

[jazty]

Keep in mind that is canadian mpg so in U.S mpg its about 12. My bus is only a 36 passeger aswell so not near as much weight to lug around.

Well now, I don't see this every day! A Canadian who actually uses imperial gallons?
Maybe it's because I live close to the US border, but most Canadians that I know of reference US gallons when talking gallons at all.. Most commonly people just use liters.

 

[Mountain Gnome]

From what I could tell going cross country and other trips:


I get 11MPG-ish on the flats at 55MPH-ish.
I get 9.5MPG-ish on the flats at 70+MPH-ish.


But I wouldn't trade my bus for a nut...:ermm:

 

[Sleddgracer]

Well now, I don't see this every day! A Canadian who actually uses imperial gallons?
Maybe it's because I live close to the US border, but most Canadians that I know of reference US gallons when talking gallons at all.. Most commonly people just use liters.

I think us more 'mature' Canucks, the ones that grew up with miles and gallons, and when 32 degrees meant winter was close, not time for shirt removal, still use real gallons as a comparison - one Imperial gal is 20% bigger than a US gal - one Imperial gal is 4.5 litres, and one US gal is 3.78 litres - to me a 5 gal pail holds 5 gals, not 18.9 litres ( 5 US gals ) - one of the big rip offs was when Canada went to the metric system and suppliers raised prices on goods because 'the new 4 litre cans cost more', and then to save money they started using US gal cans and charged more for the product than they did when it was supplied in an Imperial gal can, but then I go back to the time when my friends and I pooled our money at lunch time and bought a gallon of gas to cruise around and have enough gas left to get home after school was out - an Imperial gal of gas at that time cost 25 cents - lol - now that same quantity of gas runs about $6.50 in some areas

 

[SolomonEagle]

I have a 28' international dognose with a dt360 and a Spicer 5 speed with no od. Using Cell phone odometer and MapQuest to track millage, I have gotten 9mpg @ 63mph+/- on the freeway with the skinny pedal just shy of floored.. and including few mountain passes. When I take the coastal rout, with varying Terrain and speeds closer to 55 mph, I get just a hair over 10mpg. I plan on performing some efficiency modifications in the near future and hope to pick that average up a bit.

 

[jazty]

All these years later and it's still some form of a mess.. Grocery stores list pounds and kilograms. Residential construction still uses inches and feet.
It's sort of too bad. The metric system is sensible and intentionally architected. The imperial and US system are just legacy measurement piled on top of other legacy measurement. But we're stuck with both to make life even more complex than having only one of either

 

[Cjgoertzen]

My 6 window bus is getting the same mileage but with an older rotary pump and AT545. Since you have a manual transmission I'm surprised you are not getting better fuel mileage. What rpm are you cranking at 57 mph?

Was 2150 ish with the 9r22.5. Installed the 11r 22.5s this weekend is down to around 1950

 

[Sleddgracer]

All these years later and it's still some form of a mess.. Grocery stores list pounds and kilograms. Residential construction still uses inches and feet.
It's sort of too bad. The metric system is sensible and intentionally architected. The imperial and US system are just legacy measurement piled on top of other legacy measurement. But we're stuck with both to make life even more complex than having only one of either

the US system was put into effect because of the connotation of what 'Imperial' implied and they wanted nothing to do with it - I don't know what the reason was that they selected that particular amount to be a US gallon

 

[Cjgoertzen]

Well now, I don't see this every day! A Canadian who actually uses imperial gallons?
Maybe it's because I live close to the US border, but most Canadians that I know of reference US gallons when talking gallons at all.. Most commonly people just use liters.

I'm just a young pup but my Dad was a longhauler so thats what i grew up using. Personally don't like using liters per hundred.

 

[Sleddgracer]

I'm just a young pup but my Dad was a longhauler so thats what i grew up using. Personally don't like using liters per hundred.

I still have to translate litres per 100k to know whether I'm getting good mileage or not - lol - my Trailblazer gets 7/100 - that seems pretty good to me for a 4x4, 7 passenger vehicle with a lot of bells and whistles

 

[Cjgoertzen]

I still have to translate litres per 100k to know whether I'm getting good mileage or not - lol - my Trailblazer gets 7/100 - that seems pretty good to me for a 4x4, 7 passenger vehicle with a lot of bells and whistles

I'd say
Lol i get roughly 4.0 and as low as 3.8l/100 with my jetta. And 11/100 with my dodge 2500 cummins

 

[Cjgoertzen]

My 6 window bus is getting the same mileage but with an older rotary pump and AT545. Since you have a manual transmission I'm surprised you are not getting better fuel mileage. What rpm are you cranking at 57 mph?

It's gotta be the mountain air. Thats why your mileage is so good. Lol

 

[Sleddgracer]

I'd say
Lol i get roughly 4.0 and as low as 3.8l/100 with my jetta. And 11/100 with my dodge 2500 cummins

that's good mileage for a 3/4 ton - works out to a bit over 25 miles per lmperial gal - my 93 chevy hd 3/4 ton 350cui gets about 16 - 17 here in the mountains

 

[Cjgoertzen]

that's good mileage for a 3/4 ton - works out to a bit over 25 miles per lmperial gal - my 93 chevy hd 3/4 ton 350cui gets about 16 - 17 here in the mountains

It is very good. I drive pretty easy though. And its not stk either all off my vehicles have been tinkered with. Ive fot a 6.7 in place of where the 5.9 was running 5.9 ecu, turbo and 03 cummins injecrors. Along with a big stick from colt cams and a smarty jr cranked 220 over stk. Ita all built for mileage. Still have the factory 4spd auto which is getting changed to the nv5600.

 

[Free Bird-SKO]

Well now, I don't see this every day! A Canadian who actually uses imperial gallons?
Maybe it's because I live close to the US border, but most Canadians that I know of reference US gallons when talking gallons at all.. Most commonly people just use liters.

Hey Jazty, what transmission do you have and what does your fuel mpg look like?

 

[Free Bird-SKO]

Was 2150 ish with the 9r22.5. Installed the 11r 22.5s this weekend is down to around 1950

Thanks, let me know how it goes with the new rubber.
Seems to me I run around 2250 and up to maintain 60mph. I have 10r22.5s and 430 rear end. I had been thinking of installing a standard trans with overdrive but am now rethinking as I don't see much gain.

 

[Free Bird-SKO]

It's gotta be the mountain air. Thats why your mileage is so good. Lol

The trick is to hang a bicycle out front, that Cummins goes after it like a dog after a wiener!

I may not be doin as good as you in the 53-55 mph range, never tracked it at that speed.

 

[Cjgoertzen]

Thanks, let me know how it goes with the new rubber.
Seems to me I run around 2250 and up to maintain 60mph. I have 10r22.5s and 430 rear end. I had been thinking of installing a standard trans with overdrive but am now rethinking as I don't see much gain.

I will let you know as soon as i have some real figures. Put 170km on yesterday some stop start and a few highway km at 58mph. Already does seem better, and we still have winter fuel at the pumps