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Author Topic: Usuable Fuel Gallons from fuel tank  (Read 3056 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
1971 MC7, 8V71, Allison MT654
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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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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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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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bcaddel
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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
1971 MC7, 8V71, Allison MT654
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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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bcaddel
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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
1971 MC7, 8V71, Allison MT654
bcaddel
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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
1971 MC7, 8V71, Allison MT654
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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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RJ Long
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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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luvrbus
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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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