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Author Topic: Usuable Fuel Gallons from fuel tank  (Read 3221 times)
bcaddel
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« on: September 09, 2009, 11:10:41 AM »

I have a 1971 mc7, and it has placards on the door to the refueling area as well as on the switch panel inside the coach. Both placards say I have 144 gallon main tank and 35 gallon reserve tank. It is my understanding from looking at the parts manuel that the two tanks are plumbed together giving me 179 total fuel capacity.

I have driven the bus well over 10,000 miles and log every fuel purchase with notation on what the fuel gauge says, and how many gallons I purchased. The gauge seems to be very consistant and the readings seem to match with 144 gallon capacity. We drove from Reno to Salt Lake last weekend pulling the toad and I decided to try and figure out if I really had the 35 gallon reserve tank. I figured if I ran out of fuel I could drive the toad to the closest fuel area and purchase 10 gallons of fuel to get me going again. (I have a primer to get fuel to the filters but haven't used it yet so the pratice would do me good). It was a nice day and I had plenty of time if I did run out of fuel.

Well I chickened out when I hit 835 miles and the needle was reading 1/16 of a tank of fuel. I dropped in a weighted 1/4 rubber hose and it measured about 2 inches of fuel remaining. I purchased 131 gallons of fuel which puts me at around 1/16 of the 144 gallons remaining in the main tank which matched the fuel guage reading.

It appears I do not have any reserve tank and only have access to 144 gallons of fuel and maybe 135 of usable fuel (about 850 miles). OR is there something I have to do to access the reserve 35 gallons of fuel?

Thanks for any input
Bob
« Last Edit: September 09, 2009, 11:13:37 AM by bcaddel » Logged

Bob Caddel, Las Vegas Nevada
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« Reply #1 on: September 09, 2009, 11:32:22 AM »

Bob, I don't know about 7 but on my 8 the reserve tank was in the front bay on the passengers side.
 Most have been removed during conversion work it takes up to much space in the bays.
FWIW mine was 100 gals took up 1/2 the bay  


good luck  
« Last Edit: September 09, 2009, 11:46:11 AM by luvrbus » Logged

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bcaddel
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« Reply #2 on: September 09, 2009, 12:06:12 PM »

Bob, I don't know about 7 but on my 8 the reserve tank was in the front bay on the passengers side.
 Most have been removed during conversion work it takes up to much space in the bays.
FWIW mine was 100 gals took up 1/2 the bay  


good luck  

I think that could be it, there is an empty space in the front center of the forward bay just behind the fuel tank where I currently have my house batteries, that is about the size of what I think a 35 gallon tank might occupy. It has been diving me crazy trying to figure out if I actually had the reserve gallons or not. With your comment and my experience over the weekend I am fairly confident I do not have the reserve gallons.

Thanks for the comment
Bob
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« Reply #3 on: September 09, 2009, 12:15:19 PM »

Bob, I have the same bus.  The aux tank is in the first baggage bay, in the center against the rear bulkhead.  You can look under the bus (from the side) and see a bash guard that covers the lines.  The way these are plumbed, the aux tank does not act like an emergency reserve.  It uses gravity to fill the primary tank and will only have 2 inches of fuel in it if the primary tank only has 2 inches.  Good luck!

Glenn

forgot to mention:  the space you have your house batteries used to hold your heater core and AC core and blower motor.
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Glenn Williams
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« Reply #4 on: September 09, 2009, 01:39:10 PM »

If what tener says is fact then you may not be getting the mileage you think.>>>Dan
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« Reply #5 on: September 09, 2009, 01:59:34 PM »

What I read is Bob has a capacity of 179 gals with a reserve tank and can only put in 131 gals with 2 inches of fuel in the tank that is a difference of 48 gals that is a lot of fuel about 27% of his tank capacity 




good luck
« Last Edit: September 09, 2009, 02:07:59 PM by luvrbus » Logged

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« Reply #6 on: September 09, 2009, 02:02:20 PM »

If what tener says is fact then you may not be getting the mileage you think.>>>Dan

Dan: I am sure of the milage, I have driven the bus (COZY) 12,900 miles in the last 13 months. It was full when I purchased it and it is full now. I have purchased 2,023.6 gallons of fuel at a cost of $5,102.06. It has cost me 40 cents per mile for fuel to drive COZY and I get 6.4 miles per gallon. We usually cruise around 65 miles per hour, and I assume we would get better milage if the wife's foot wasn't so heavy.

I am still not sure if I have that 35 gallons of reserve fuel since Glenn said the extra space in my baggage compartment used to hold the heater and AC core. I will need to look and see if I can find the plumbing from the aux tank to the main tank. My current thought is the Aux may be gone because of only having 2" of fuel and it only took 131 gallons to fill it up.

I will let you know if I figure it out.
« Last Edit: September 09, 2009, 02:21:49 PM by bcaddel » Logged

Bob Caddel, Las Vegas Nevada
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« Reply #7 on: September 09, 2009, 05:16:01 PM »

Hello ,I also have a MC-7 with 179 gallons of fuel capacity . The 40 gallons or whatever the Aux. amount is, isn't exactly like a reserve tank.On all my Harley-Davidson motorcycles let you switch to reserve if you ever 'run out of fuel. In my MC- the fuel tanks both drain together in unison at the same time at the same rate. So when you are low on fuel you DO NOT have an additional 40 gallons in "RESERVE" . I truly hope that helps or did I make it clear as mud? Good luck! Thank you ,GFC
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« Reply #8 on: September 09, 2009, 06:45:20 PM »

How are you measuring your distance travelled?

How have you determined it is accurate?

Which gallons are you using, US or imperial?

Unless you do pretty much nothing but open highway driving,

6.4 MPG US seems a little high average for mixed driving for an 8V71 and auto drive train.

6.4 MPG IMP, now, that sounds closer to a good number.

happy coaching!
buswarrior
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« Reply #9 on: September 09, 2009, 07:48:04 PM »

How are you measuring your distance travelled?

How have you determined it is accurate?

Which gallons are you using, US or imperial?

Unless you do pretty much nothing but open highway driving,

6.4 MPG US seems a little high average for mixed driving for an 8V71 and auto drive train.

6.4 MPG IMP, now, that sounds closer to a good number.

happy coaching!
buswarrior

buswarrior
Not sure if you are kidding or not, but just in case, the hubmeter matches almost exactly with the GPS milage and the speedometer matches with the GPS miles per hour. so I am fairly certain the milage is correct. We have been in 30 states so far (both coast) and I haven't seen any dispensers using Imperial gallons. We are hoping to go to Alaska next summer and if I remember from my days of flying super cubs through Canada on my way to Alaska back in the late 70's, you guys do have imperial gallons up there so I will need to do some converting through Canada.  Shocked Cheesy

You are correct in that we do mostly highway driving but that is what we enjoy.

What kind of milage do you get and what would you expect our rig should achieve pulling a toad. We do a lot of mountain driving out here in the west, my dad said he usually averaged just under 7 mpg back in Texas but I assume that is because it is fairly flat and he didn't often pull a toad.
« Last Edit: September 10, 2009, 05:56:54 AM by bcaddel » Logged

Bob Caddel, Las Vegas Nevada
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« Reply #10 on: September 09, 2009, 07:54:00 PM »

Thanks GFC
I think I understand how the reserve tank works on the bus now, so the only think I have to do is figure out for sure if the tank has been removed (which I assume it has).

What kind of range do you have between fill ups and/or what do you get for MPG?

Bob
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Bob Caddel, Las Vegas Nevada
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« Reply #11 on: September 10, 2009, 01:04:56 AM »

Bob -

The dashboard/fuel door placards with the fuel tank capacities was a "one piece fits all" part - used on coaches with and without the first-baggage-bin-mounted reserve tank.  Kept costs down in the parts department.

As was mentioned earlier, the "reserve" tank was actually inside a big square box that sat centered under the tunnel and against the back wall of the first luggage bin.  They were an absolute nightmare to remove - most converters left them alone, unless they were leaking.  And a clue that your coach may have been a 'Hound, if in fact it does have the extra tank, is a quarter round shelf mounted high on the back wall of the first luggage bay.  These were used to hold tire chains, and I've only ever seen them on Greyhound MCIs.

Glenn is also correct about the way the reserve tank fills/empties.  And additional trivia - the extra capacity was only available on the 40-footers.

As for mileage, 5.5 - 6.5 overall is a good rule of thumb for an MCI using US gallons.  Save yourself the grief of having to reprime, and figure fueling at 500 - 600 mile intervals.  A very common, safe and free (!) way to avoid having to prime your engine at Oh Dark Thirty, and a guideline used by a lot revenue service operators.

Pulling a toad will have a negligible effect on your overall fuel consumption, especially if it's a lightweight and you're running the flats.  They sorta tuck themselves into that vacuum that's created by the bus punching it's way thru the air.  Running Rocky Top out west will drop you into the under-6 range, mostly because of having to use the lower gears.  Think pulling Donner from Sacramento to Reno on I-80.

FWIW & HTH. . .

 Wink
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« Reply #12 on: September 10, 2009, 05:52:19 AM »

Hi Bob.

Excellent report.

There are many who have not checked the accuracy of their instruments, making their fuel economy calculations worthless.

However, not in this case, sounds like you're mileage is good.

My MC8, 8V71/HT740 gets 7 mpg US at 60 mph, and 6 mpg at 70 mph out on the open road. Tanks that have in-city driving will show a degradation down below 6 mpg, depending on the amount of start/stop driving.

No more imperial gallons up here since the 70's. We use metric litres. 3.78 litres to the US gallon, 4.54 litres to the old imperial gallon.  Have to watch, many Canadian busnuts still figure in imperial.

happy coaching!
buswarrior





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« Reply #13 on: September 10, 2009, 05:57:35 AM »

I've always felt that running my tank down too far would increase the potential for plugging the filter with debrie from the bottom of the tank, what I normally do is stop every 250 to 300 miles and top the tank off, it gives me a chance to get out and stretch my legs and move around a little.  We don't drive very far in a day anymore either, 300 miles is enough for me, I never seem to be in any hurry anymore anyway
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« Reply #14 on: September 10, 2009, 06:11:32 AM »

You guys still haven't answered Bob question on why a 179 gal tank only hold 131 gals in 10,000 miles of driving he has the fuel mileage figured out

good luck
« Last Edit: September 10, 2009, 06:23:36 AM by luvrbus » Logged

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« Reply #15 on: September 10, 2009, 06:26:33 AM »

Thanks RJ for your responce, it appears I definitely do not have the aux tank so I only have a total of 144 gallon capacity.  As Cody mentioned we don't want to run the tank on the bottom 1/4 tank normally but I feel we need to know what is available for those times when we might need it.

Before Pilot purchased the Flying J's we would always try to stop at a Flying J so we had access to propane, dump station and cheap fuel price. Sometimes that would cause us to stretch our milage to get to the next "J". It appears the Flying J's are changing their pricing strategy now so they most likely won't be the cheapest price anymore but they are still RV friendly, so we will still use them and sometimes we have to dig down a little deeper into the fuel tank to get there. My fuel gauge seems to be right on so I will rely on it and my milage (and 144 tank capacity) to see if I can make it to the closest "J".

Buswarrior
Do you run in the same gear when driving at 60 vs 70. We have a MT645 "5" speed transmission and when I want to drive at 60 I shift into 4th and run at 2300 rpm. It seems to run cooler and holds right at 59/60 mph. If I shift into 5th it wants to run up around 65 to 67 at 1800 rpm but it runs a little hotter and I assume burns a little more fuel but I havent been able to define that since I do both during each fill up.

bob
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Bob Caddel, Las Vegas Nevada
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« Reply #16 on: September 10, 2009, 07:02:08 AM »

Bob, it is a good idea to run all the fuel out and drain the tanks I do it about every 3 years even living in the desert doing this I don't change fuel filters till around 25,000 mile mark and they are still good



good luck
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« Reply #17 on: September 10, 2009, 07:12:15 AM »

Clifford, I agree with you on the filters. I think I will bring the coach home almost empty next time and drain the tanks to see what might still be in there.

Our bus had been sitting for about 4 years when we purchased it. The filters plugged up out on the highway in the mountains of Colorado. We drove at 20 mph for about an hour to get to a truckstop to purchase new filters and change them. We always carry spares now.

The bus started running rough about 7000 miles later and I pulled over and put on the spare set  and it cleared up right away so I might have some gunk down in the bottom of the tank.
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Bob Caddel, Las Vegas Nevada
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« Reply #18 on: September 10, 2009, 08:08:18 AM »

Bob, you will use less fuel at 1800 rpm than at 2300 if the heat goes up a little increase your speed sounds like your dad had the bus setup for 70mph some guys would love 70 mph at around 1900 rpm and I would not worry about the heat if it stays under 200 degrees 



good luck
« Last Edit: September 10, 2009, 08:14:10 AM by luvrbus » Logged

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« Reply #19 on: September 10, 2009, 06:28:59 PM »

Mine has 4 gears, so same 4th gear for 60 or 70 mph.

I turn governed speed of 2100 rpm at 70 mph. Engine turns somewhere 1850 rpm to make 60 mph.

I agree with luvrbus, you'll see some good fuel mileage if you stay in top gear at 60 mph.

The 8V71 is better at fuel consumption in the 1750 to 1950 rpm range than up high.

Temperature wise, it sounds like you are seeing it running against the thermostats turning 2300 rpm in 4th gear, the fans and water pump are shedding all the heat and then some.

What kind of temps are you seeing in 5th at 60 mph?

You may have some hidden economy in your gear choice!

happy coaching!
buswarrior
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« Reply #20 on: September 10, 2009, 07:14:15 PM »

buswarrior (thanks for asking)

I would like to give some history prior to giving the temp numbers. We drove from Texas to Nevada last September and took a 7500 mile trip around the country the whole month of May this year, plus several trips around Nevada this summer.

The engine seemed to stay in the 185 range during all of this travel and in the past I have not had the temp go much above 190 at anytime except when I would be driving up a mountain grade. I have misters and I turn them on if I get close to 200 and keep them on until I crest the mountain top then turn them off. I am usually around 180 when I turn them off at the top of the mountain.

Last weekend we drove from Reno to Salt Lake, it was only about 88 degrees outside. We were traveling on level ground, in 5th gear running between 1800 to 2000 rpm's (no cruise control) and around 65 mph. The temperature hit 200 after about 2 hours of driving on level ground. We turned on the misters and it cooled right off, but when we turned the misters off it started going back above 190 and crept up to 200 degrees (misters off) which had only happend once before in Texas last year but it was 104 degrees outside then.

The misters always cool it down but as you know there are problems with using the misters too much on the radiator so we try not to use them. On the way back home from Salt Lake we ran in 4th gear and 2300 rpm and it never went above 190 even on the hills. We left Salt Lake at 6:00 in the morning and was back in Reno by 3:00 in the afternoon so the outside temp was 10 to 20 degrees cooler than when we had the problem.

Nothing has changed with the bus so I am a little concerned about the 15 degree rise in engine temperature. I have an almost new engine and the radiators were taken out and redone about 20,000 miles ago and really look good. The cowling is all sealed up and I don't think there are many if any air leaks and I don't loose any coolant so I am just a little worried about what I might face next summer.

I would appreciate any suggestions or comments on what could be causing this problem. The temp guage on the dash match the temp guage in the engine compartment plus I carry a Temperature gun that confirmed the temperature when I pointed it toward the thermostat area.

Suggestions?
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Bob Caddel, Las Vegas Nevada
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« Reply #21 on: September 10, 2009, 07:31:13 PM »

I would be highly suspicious that air is getting past the fan door seals, or otherwise around the radiators instead of through them.

On installing new-to-me rads in my MC8, heretic that I am, I used a can of spray foam to seal around the rads, using the tired shards of rubber seal to act as a base for my foaming. Sealed up tight and easily chewed out the next time rads have to come out.

What shape are those seals in?

For the fan door, run the engine on fast idle, get a ladder, and check around the door for evidence of air sucking past. Smokers may blow smoke, others may use tissues or whatever, look for it sucking air in where it shouldn't.

If you get some wind through there, fear not, I continue to use duct tape around the door in the appropriate colour to seal mine until I get around to improving the situation. I am dissatisfied with how small the stock seal contact surface is, I want to do an upgrade to bigger stuff.

Any corrosion opened up the ceiling or floor of the fan compartment? 

Some chunk of rubber blocking at least some of the gap that the fan belt goes up there through?

Air getting past is guilty until proven innocent, before I'd move on to more complicated diagnosis.

happy coaching!
buswarrior
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« Reply #22 on: September 10, 2009, 10:33:19 PM »

Hello all , o.k. i just got into my flame proof suit.  I getWAT better fuel mileage than 6.5 unless I'm climbing big hills.BUT...The bus I beleive has hi highway gearing i.e. low numerically. The coach is not heavy currently gutted but the 6.5 is worse then the worst mileage I've ever gotten keepin SCRUPULOUS track of miles gallons fuel used etc....OK go ahead flame suit is intact and fully functional LOL
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bcaddel
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« Reply #23 on: September 11, 2009, 05:54:17 AM »

gfcgfc1
OK, I will bite, what kind of fuel milage do you get?

I would also be interested in what RPM & speed do you usually run?

What temperature does your engine operate at when running down the highway?

and last but not least how many gallons do you have and what do you consider your range on a full tank.

Thanks for info
Bob
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Bob Caddel, Las Vegas Nevada
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« Reply #24 on: September 11, 2009, 05:59:42 AM »

Buswarrior

You gave me some great ideas on the air flow. I have not checked the area where the fan belt goes up to the fan, or the fan door. Looking at the radiators from the outside, it has been sealed with that spray foam stuff so I assumed it was sealed everywhere but I haven't confirmed (or even looked) at the inside area.

Bob
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Bob Caddel, Las Vegas Nevada
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« Reply #25 on: September 11, 2009, 09:02:51 AM »

Hello , Bob , my MC-7 has 179 gallons fuel capacity.6.8 is the worst mileage I have gotten. That is thru the mountains in NewMexico headed west . 7.5 average up to a high of 9plus all highway . 4 speed Spicer Manual trans. I stay under 70mph.The Tachometer is inop. now so I cant tell RPM's.not very  high tho by ear.The bus is not a jack rabbit or hot rod .Engine runs very strong and smooth almost no smoke except under HARD acceleration and big hills out west NewMex and Northern Arizona. I havent checked the gears in the differential ,  is there a 3.3xx ratio available for the rear end? That is what I think /suspect it has.OK FLAME away! LOL!!    GFC
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« Reply #26 on: September 11, 2009, 10:05:13 AM »

Gf, I don't think a 3:33 is available for a MCI 7 Richard on the board here cut the center section out and installed a different one to get taller gears on his 7.
No body here is going to flame you about your post on your mileage first liar here doesn't stand a chance according to John Ed       LOL 
PS I believe you I have a 05 Eagle with that set up that gets great fuel mileage   



good luck
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« Reply #27 on: September 11, 2009, 11:43:24 AM »

gfcgfc1,

Congratulations, that sounds pretty darn good to me. I am fairly certain that I have the 3.7 rear end. My speeds and rpm's & tires match that setup so I am fairly confident. I have never got over 7 mpg but have got close on one or two fill ups, but that is probably mostly from possibly not getting it topped off each time.

How slow do you get when going up some of those long 6% grades? I seldom drop below 30mph but I have a couple of times on some on the longer grades. I just turn on the flashers and give thanks for the passing lanes.
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« Reply #28 on: September 11, 2009, 12:14:38 PM »

Hello all , Bob I have been thru 2nd gear and into 1st gear scared and praying till the top.Then all gleeful and triumphant , like I did something,LOL!!
The temps normally 185 - 190 Than sometimes my shutterstadts act backwards and close when hot urghhhh! Temps come right down tho . This bus is geared for the highway with no hills .But I live in the Rockies! What is lhe lowest numerically available gear set for this differential, 'cause I'm confident that I have it. If 3.3xx isn't available what is close to that, that comes in a MC-7?3.5xx?Love the mileage hate the gear in the hills.Maybe more gears in the tranny would help.Roadranger ten speed would that help cut the hill?
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« Reply #29 on: September 11, 2009, 06:57:12 PM »

stick shift 4 speed will get better fuel mileage than an automatic.

In revenue service, it was considered that the auto lost 1 mpg over the stick shift.

Did the MC7 have a different axle from the MC8/9?

I'd have thought the same Rockwell limitation of stuffing a 3.36 or whatever it is into that axle would work on the '7, same as the newer ones.

Educate us, please!

happy coaching!
buswarrior
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« Reply #30 on: September 11, 2009, 07:57:44 PM »

Buswarrior
Is it the general consensus that a stick shift will average 1 mpg above an automatic?

Even at that expense, from my experiance I think it may be worth it.

Bob
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« Reply #31 on: September 11, 2009, 08:18:20 PM »

in busnut use, the practical issue is how many miles will be driven each year?

Very few busnuts drive far enough for anything to really matter in fuel economy terms in the choice of transmission.

An auto driven well will match or beat a stick driven poorly.

Drive both like the devil is chasing you (in other words, revenue service with a paid wheel holder) and the spread will hold.

Pick the transmission that your co-driver is likely to be happy with?

Once you get into the Allison World family of transmissions, and the automated manuals, everything gets blurred some more.

happy coaching!
buswarrior





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« Reply #32 on: September 13, 2009, 11:06:51 PM »

I just returned from a 5,000 mi trip in my 4104 with 671 and 4sp manual. I crossed the Rockies and Cascades two times each and climbed some pretty impressive grades.

I found that after climbing in 4th gear and getting the engine around 200*F or slightly higher that when I shifted down into 3rd (or 2nd a couple of times) that the temp would immediately go down.

I assume this is caused by the fact that the lower gear makes the engine work less and the fan is turning faster and the coolant is circulating faster.

This same thing would apply when running in 4th instead of 5th, the engine is working less in the lower gear.
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