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The Slims 08-28-2006 12:06 PM

Well we just took our first trip (to Bristol, TN) and managed about 9.5 MPG with quite a few hills although we're still pretty empty inside. We we're unable to get an average for the entire trip since we broke an injector line and pumped out a BUNCH of deisel before we noticed and could get off the mountain we were on at the time. Side note: We miraculously found a replacement line in Johnson City and were back on the road in no time.


the_experience03 08-28-2006 08:03 PM

Isn't that a pain? I disconnected my veggie oil return line prior to leaving for one reason or another and never hooked it back up. Well this meant there was nothing holding up the slid down and the valve on the veggie oil side was popped open. I'm sure SOME fuel returned to the diesel tank at the time, but I KNOW a lot more just kind of pumped all over the engine compartment. Oh well...such is life. A piece of speaker wire did a darn find job holding the apparatus up and out of the way so it never happened again.

JoeA 12-28-2006 06:26 PM

mileage,engine,gearing &gvwt?
I get 8-10 regardless of terrain. Usually closer to 8. I have dt466. It has 4:76 gear ratio. I never have my foot to the floor to maintain speed. once its up to speed I actually don't press it all that much, just enough to keep it pushing those low gear ratios. This is why I think 4:10 gears would be fine. I might get a steady 10 with an occasional plus or better(10-12), run quieter at 55 and get a top speed of 67mph at the same rpms 55mph is now. I would love opinions on this. In fact I may post a whole new forum on this for feedback. My GVWT 25,800. I actually weigh 19,500 with full fuel and 55 gal of water and all my belongings. I live in this thing.

kotflb 12-29-2006 03:53 AM

Hello JoeA, I too have the DT466, but mine is not aftercooled. I bought my bus 900+ miles from home and got 10mpg (actually 10.4 mpg) on that trip. The bus had all the seats in it and weighed 19.490, full of fuel. Mine has the MT643 trans and 4:44 axle ratio. I was running 60mph at 2260 rpm, on 295-75/22.5 tires.

I've talked to several owners and drivers of m/d trucks that are running this same engine and some have the auto trans, while others have the the 5 speed 1:1 high gear and most of these guys have the 4:10 axle ratio. Of the ones that run several states with this setup, they are not happy campers, when trying to average 65 mph. Now there trucks will hold 65mph, but the fuel mileage is better at 6o to 62 mph. And some of the ones that own their own are even talking about changing their axle ratios down to 3.7 and even 3.55 for faster cruising and less engine noise. Of course these trucks run over 2k miles a week so maybe they know whats what with these power trains. I'm taking the wait and see approach, I too would like to get a 65mph cruise speed down to less than 2000 rpm.

Les Lampman 12-29-2006 08:26 AM

Hey Joe,

Those numbers don't work out quite right; all the charts I found on the 245/75R22.5 tires say they're 37.1" to 37.4" in diameter.

What speeds at what rpm's are you getting now?

This is the online calculator I've used for all my computations:

I have a DT466 in my 1979 Blue Bird full size (66 pax) bus. I drove home from Denver to north of Seattle and made three round trips (1400 miles each) to northern California from NW Washington. Lots of hills on all my trips! On the flats I get just a hair over 9 mpg (usually about 9.2) , in the hills I'll drop into the low 7's. On the trips to California I average about 8.5 mpg.

I run at 55 mph at 2400 rpm. Wide open, foot on the floor, hoping for a tailwind speed is about 57 to 58 mph at 2600 rpm.

If you use 2600 as the rpm, 4.10 for the rear-end, 1.1 for the final gear ratio (allowing 10% slip on the AT545), and 37.1 for the tire diameter that comes out to 63.6 mph. You'd be around 2450 rpm for a 60 mph cruise.

To get to your hoped for numbers it seems you'll have to go a little numerically lower for your rear-end. A ratio of 3.70 would give you 60 mph at 2200 rpm and 70 mph at 2600 rpm (is that your governed rpm?).

What's really hurting you are those itty-bitty tires; do you have room for something taller (like 11R22.5)?

JoeA 01-06-2007 05:04 PM

Thanks y'all
Thanks for all the great info. i'm on vacation and will have a chance to reply in a few days.

JoeA 01-14-2007 02:14 PM

yeah the tires are low profile and a 35" diameter.
You are right, my calculations are a bit off I would be about 63mph at the same rpms i am now running 50-55

60mph @2260rpm doesn't sound too bad for your 295 tires

KevinCoughlin 02-05-2007 01:09 PM

Just took a longer trip - my bus (66 passenger, no outrageous body work or lifts, 392 V-8 international running propane, not gasoline) was being used as a moving truck. Fully loaded nose to tail, and towing a Geo Tracker, over the mountain passes from Seattle to Spokane. I found my stock tach was bad - it actually cruises at 55mph at 3200 rpm (the "sweet spot), 60 is about 3500 (what I was driving) and 3600 is redline. Most of the trip was at 60. The passes slowed me to about 25 to 35 mph.

My first trip with the empty bus bringing it home from the school bus yard (200 miles) I averaged 3.25 mpg at about 50 - 55 mph, totally empty and mostly flat. Now, with MSD ignition, fresh tuneup, proper advance timing for propane, and a cold air intake running at 60, fully loaded with a car in tow, I still got 3.25 mpg. VERY frustrating. (The passes were actually 2.85 mpg).

Either - propane is MUCH more inefficient as a motor fuel than gas.... or there are still some things I just haven't found to fix. I may have to drop a 4 bbl carb on there just to try it with gasoline - but at this mileage it means a new bus (can you say Crown? 10 speed?) is in my future for long trips.

Still.... the ride fully loaded was nice - it drove like a dream - and I never even noticed the toad was behind me except when looking for a place to park. Maybe a turbo?

I did notice that ALL the big diesel trucks have much lower front bumpers and air dams for aerodynamic reasons, and all the school buses out there have these "wings" on the back to break up the airflow over the tail. This seems to be a cheap and easy modification - I'll have to try that as well.

pete c 02-11-2007 12:43 PM

I own you guys!!!! :lol: 18 mpg, 22 ft '86 toyota sunrader. 22RE auto.

I just bought this thing and plan on doing a lap around the country this summer. Reading this board and a few others though have got me jonesin' for a bus....real bad. Problem is, I hate the thought of settling for 10 mpg. I think it can be beat.

What is the most economical engine to run? I am guessing that the 5.9 cummins in a shortbus with a 5 speed and hiway gears ought to do pretty well. This engine will get low twenties pulling a 1 ton dodge pick'em up. I would think that a light shortbus, sorry, no jacuzzi, driven at 55 mph ought to be able to break 15. Which means if I buy that dude's silly wing, I'll get 45, right? :lol: :lol:

Are there short buses out there with this setup?

Excalibrate 03-12-2007 10:33 AM

Depends on how fast I wanna go. At 68 to 70 I only get about 8.5 but with a little more patience (60 to 62) I'm only at 2200 rpms and get nearly 11. TC2000 35' 5.9 AT545 4.33 and 41" tires. Heck I'm happy with that . . .

BTW if you calculate cubic footage per mile per gallon I beat the heck outa that toyota. It's like Einstein says "It's all relative to your perspective" :lol:

the_experience03 03-12-2007 07:18 PM

Cubic footage per mile :lol: I've never heard that before, but it makes sense. I think trains that get 20 gallons to the mile (yes, gallons to the mile) win. Last I heard it took 1 gallon of fuel to move 1 ton of freight about 400 miles.

oakspring 03-25-2007 10:37 AM

Big Gary: 30 ft, 54 passenger International S1800 Thomas Built Bus

Engine: 9.0L Diesel
Trans: AT545 Allison 4 SPD Automatic
Rear: Spicer 6.50 ratio

Fuel MPG:
High: 13.41 mpg
Low: 4.04 mpg
Avg: 7.47 mpg


Las Vegas, NV......Starting point
Boron, NV............183.5 miles....28.402 gallons....6.46 mpg
Bakersfield, CA....113.7 miles....15.720 gallons....7.23 mpg
Madera, CA..........121.8 miles....15.898 gallons....7.66 mpg
Willows, CA..........226.6 miles....23.578 gallons....9.61 mpg
Redding, CA..........71.9 miles....17.800 gallons....4.04 mpg Tough hills and mountain climb
Eureka, CA..........162.2 miles....15.133 gallons....10.72 mpg
Shingletown, CA...176.0 miles....33.975 gallons....5.18 mpg
Reno, NV.............174.3 miles....13.001 gallons....13.41 mpg Very flat out running
Rye Patch, NV......112.2 miles....14.870 gallons....7.55 mpg
Carlin, NV............152.2 miles....29.790 gallons....5.11 mpg
Wells, NV..............72.7 miles....14.290 gallons....5.09 mpg
Lakepoint, UT.......157.4 miles....17.986 gallons....8.75 mpg
Evanston, WY.......105.8 miles....17.865 gallons....5.92 mpg
Rawlings, WY........208.6 miles....25.658 gallons....8.13 mpg
Larkspur, CO........283.4 miles....39.301 gallons....7.21 mpg
Pueblo, CO.............66.3 miles end of trip

As you can see the mileage per gallon varies quite a bit dependent upon the terrain. Also consider the configuration of your rig. One of the reasons I want to change out my rear end gearing is to improve highway speeds and gas mileage, but in doing so I will loose some climbing muscle for tackling hills and mountains. Such is life.

I hope this helps

the_experience03 03-25-2007 07:54 PM

That's a cool list! It's tough to get accurate numbers in a single tank just because the diesel fuel foams so much.

It's interesting that your mileage varies so much. Mine varies by maybe 2 mpg total. The worst tank I've seen is about 6.5 mpg and the best was ovre 8, but 8 mpg is a pretty solid figure to bank on for me.

oakspring 03-25-2007 08:18 PM

This trip covers a lot of various terrain, from flat cross country driving to gradual climbing to city, to step hard climbs pulling serious grades and some pretty tough combinations of all of the above. The best mileage of course was on the long level steady flats, hills and mountains are the worse. But it's important to realize that you can have a lot of variation.

I'm hoping with a new set of gears in the rear end I can improve both the speed and gas mileage.

the_experience03 03-25-2007 08:45 PM

My worst mileage was across North Dakota which happens to be as flat as any state I've ever seen. It doesn't matter which direction you're traveling in across North will ALWAYS have a 25 mph headwind.

Excalibrate 03-26-2007 09:11 AM

Sounds kinda like the story your grandparents told you about having to walk to school, barefoot, in the snow, uphill, both ways! :P

boojiewoojie 08-08-2007 10:02 PM

Re: What kind of milleage do you get?
Okay, just took a long trip (5,326 miles) so I think I have a good idea what my mpg (or lack therof) is.
Low: 6.3 (Redding, CA to Reno, NV)
High: 9.0 (Cheyenne, WY to North Platte, NE)
Average: 7.43
I filled up 22 times (60 gallon tank so I always stopped every 300 miles). We went from Lewisburg, TN to Reno, NV to Ferndale, CA and back. I hate driving the interstate but we had limited time so we went all interstate. On the way out I had a canoe and a small airplane fuselage strapped to the top and on the way back had the same canoe and two 2'x4'x8 boxes of foam strapped to the top. I did get asked if I was on my way to Burning Man...
My bus has an air throttle so I never had my foot all the way to the floor. Even though I kept an eye on the exhaust (it has a driver's side exit) to keep it in the "sweet spot" I don't know if it really made a difference. Level speed is 62 mph (verified by the radar speed limit signs), down a 6% hill is 65 mph and I actually hit 70 once. My slowest speed was 15 mph going up the I-80 grade outside Salt Lake City and several other times. I love the scenery at slow speeds... I got pulled over by a sheriff's deputy comeing from Susanville, CA to Reno for "impeding traffic". Didn't get a ticket since it was one lane construction and there was no place to pull off. My wife thinks they pulled us over so they could check the bus out- she overheard one of the deputys tell the dispatcher that it was a "cool bus conversion"...
With my non-turbo'd 3208 I can pretty much tell my altitude- the higher it is the more it smokes. Here in Tennessee it doesn't really smoke at all.
My favorite state was Wyoming- one of the jokes posted at the welcome center:
"When the wind stops blowing the cows fall over." The wind blew so hard it shifted the load on top about 8" to one side.

DizzyIzzy 10-03-2007 04:06 PM

Re: What kind of milleage do you get?
Now I have only drivin my bus from Wisconsin to Georgia. But on the ride I averaged around 11mpg. It was a hoot to drive too.

FACPTECH 03-09-2008 12:58 PM

Re: What kind of milleage do you get?
New kid on the block, having just found this website.....and I must say, Thank God, 'cause I've been a-lookin' for a looooong time!

Recently purchased a 1989 Chevy 72 (?) passenger Blue Bird, ripped out the seats and did the conversion myself. ((Pictures coming soon)).
I had expectations of 5mpg (or worse) with the 366 ci motor and auto tranny, so on our first trip, I kept the speed around 55-60 mph. I approached the gas pump with an open mind, but was ecstatic to find I had averaged 8.8 mpg. I don't have a tach (yet) so I don't know what rpm it turns at that speed, but it sounds fairly high, maybe 3300 or so? I do know that a couple of times (downhill) I hit 65-70, and it sounded as though pistons and valves were about to leave their respective places within the motor, so I kept it under 60mph from them on. The second fill-up was only 8.5, but most of that was in the Ozark mountains of Arkansas, and it's tough to get above 40-45 mph on those windy roads.

Has anyone successfully replaced their rear-end with a higher gear ratio, and at least maintained their mpg? I would love to be able to cruise at 60-65 mph, and not have the motor turn near red-line like that. I would think it would last much longer.

Billsman 04-01-2008 12:30 AM

Re: What kind of milleage do you get?
I'm at 11-12 miles a gallon.

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