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Old 10-15-2019, 06:23 PM   #1
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New bus rolling: questions

I am on the way in the new bus since noon today. Heading east on US Highway 50 by Dodge city Kansas currently. I have an issue that I hope the collective wisdom of Skooly.net can help with.The fuel gauge is acting crazy, I think. When I fill the tank to the tippy top the gauge reads half full. Then I go down the road 100 miles in the tank drops back from half full to a quarter The fuel gauge is acting crazy, I think. When I fill the tank to the tippy top the gauge reads half full. Then I go another 25 miles and itís hovering on E . I topped it off again and had to add 11.8 gallons, so Iím not using massive amount of fuel and thereís no leak that Iím aware of and . I topped it off again and had to add 11.8 gallons, so Iím not using massive amounts of fuel , Unless you consider 8 miles per gallon a tremendous loss (Iíve been heading into a pretty stiff headwind this afternoon and running at a 65. Is there anything that I missing? Some kind of reserve tank function or something like that that has me getting the wrong reading or misunderstanding. Itís a little bit nerve-racking to be driving out in western Kansas on the wide open Prairie running on E. With Knightfall on the way. By the way, Iím hoping to make it to Hannibal Missouri before I shut it down to get some sleep.

By the way, I wish I wouldíve had time to put a CB radio in the bus . I have a barely used cobra 29 at home that I will install ASAP. As soon as I get motorhome plates, a top-notch radar detector will become part of the equipment as well as soon as I get motorhome plates, a top-notch radar detector will become part of the equipment as well
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Old 10-15-2019, 06:33 PM   #2
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Sorry about the repetitive sentences and Iím using dictation on an iPhone and for some reason it is it it has a habit of doubling whatever Iíve dictated. Kind of frustrating
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Old 10-15-2019, 06:34 PM   #3
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The bus is a 2008 Thomas HDX. The one that’s in my profile.
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Old 10-15-2019, 06:45 PM   #4
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Breaking news. I stop for half an hour to get something to eat now the tank is back up to half again. So onward I go. Other than that the Thomas rides like a dream it goes down the road better than my car. It tracks straight and true and it rides like it’s on air.I have to watch my speed because it creeps up past 70 without me noticing. I’m trying to run closer to 60 to see if the mileage gets better.
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Old 10-15-2019, 10:17 PM   #5
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do you know how many gallons you tank is? If so then at least you can estimate your range based on 8mpg, and leave some extra wiggle room. It is what I do, fill up based on miles driven.
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Old 10-15-2019, 11:39 PM   #6
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Yes I believe the tank is around 60 gallons I just stopped again to get some fuel and found that I’m getting about 7 1/2 miles per gallon. That’s like a modern semi truck pulling a 40,000 pound load +18,000 pound tractor . I had heard that the C7 engines were bad on fuel consumption but this is kind of disappointing. Maybe there’s stuff that needs to be done in the way of a tuneup.

There is one outfit that I found that will reprogram your ECM on the cat C7 for better mileage and more power. The trouble is the wholesale price on the tune is $2800.That’s as opposed to a “rerate” by caterpillar which you could get for about 500 but of course they leave all the emissions programming in tact and certainly don’t allow you to delete any emissions equipment.
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Old 10-16-2019, 02:22 AM   #7
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Yes I believe the tank is around 60 gallons I just stopped again to get some fuel and found that Iím getting about 7 1/2 miles per gallon. Thatís like a modern semi truck pulling a 40,000 pound load +18,000 pound tractor . I had heard that the C7 engines were bad on fuel consumption but this is kind of disappointing. Maybe thereís stuff that needs to be done in the way of a tuneup.

There is one outfit that I found that will reprogram your ECM on the cat C7 for better mileage and more power. The trouble is the wholesale price on the tune is $2800.Thatís as opposed to a ďrerateĒ by caterpillar which you could get for about 500 but of course they leave all the emissions programming in tact and certainly donít allow you to delete any emissions equipment.
7.5 is pretty darn good for a full size school bus.
My 92 Ward only got like 7.

All that money deleting emissions equipment could be used to buy a complete running bus without any emissions stuff.
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Old 10-16-2019, 02:27 AM   #8
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I do hope the fuel gauge is the least of your problems on your journey home.


My CAT 3126 has a lifetime fuel consumption of 6 MPG ... but I have recorded 10.4 MPG on a 300 mile trip. I've not made any long trips in the last 3 years to see if that s still true.
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Old 10-16-2019, 06:49 AM   #9
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well makes me feel good that my old gasser is getting 6mpg consistently.

You can measure the length, width, height of your fuel tank and calculate cubic inchs, divide by 231 to get gallons.
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Old 10-16-2019, 07:28 AM   #10
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I took my Gasser Superior out on a Nice shakedown run with its new rear gears.. (4.7.. at 62 im getting close to 7 now on gasoline... yeah!!



as for the OP.. the sending units typically go out on busses.. they are an easy replacement.. there should be a square metal panel in the inside floor of your bus right above the fuel tank.. under that panel will be your sending unit.. make sure the wire connections are solid to it and ground is good. if that checks out, chances are the sender is shot.



I have had bad luck with the cheap-O amazon replacements on my internationals.. not sure if the freightliners will be same or not .. but might be inclined to go OEM.. oh and when you convert dont cover up access to that plate in case you need a new sender again..



Native - the Lifetime MPG is almost always low on a school bus because it ran stop N go N idle rourte service.. and now we are turningthem into road trip warriors where they get in top gear and cruise down the highway we almost always beat the lifetime MPG stored in the computer
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Old 10-16-2019, 08:34 AM   #11
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Are you still running a carburetor on the superior? 7 is my target mileage, I just have not had time to mess with fuel management lately.
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Old 10-16-2019, 08:42 AM   #12
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...All that money deleting emissions equipment could be used to buy a complete running bus without any emissions stuff.
Spending that kind of money only makes sense if you are a commercial operator logging 150k miles per year, in which case gaining 0.5 mpg would result in savings of around $5000 per year in fuel costs.
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Old 10-16-2019, 09:01 AM   #13
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It seems like small Diesel engines pushing big loads get worse mileage than big ones with tall gears and the same loads. My class eight tractor used to get 7 miles per gallon at a gross weight of 40,000 pounds (I was always lightly loaded) The tractor running down the road by itself could get 14 miles per gallon. Makes me think that if you could stuff a 14 liter semi-truck engine into a bus you could probably get 12 miles per gallon.
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Old 10-16-2019, 09:10 AM   #14
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It seems like small Diesel engines pushing big loads get worse mileage than big ones with tall gears and the same loads. My class eight tractor used to get 7 miles per gallon at a gross weight of 40,000 pounds (I was always lightly loaded) The tractor running down the road by itself could get 14 miles per gallon. Makes me think that if you could stuff a 14 liter semi-truck engine into a bus you could probably get 12 miles per gallon.
The gearing probably has as much to do with it as the engine. school buses are geared for stop and go. Trucks are geared for long hauling mostly.

Are you SURE you have a "300 hp" C7 variant? Most school buses have 170-230 hp ratings. The higher rated C7's have several differences to the lower rated ones. I have a 190hp 3126 and the highest I can rerate is to 210.
I'm getting at least 10 mpg in my 5 window shorty but it doesn't have typical school bus gearing. Its 3.42 and it does great on the interstate. Even has the lamented 545 transmission.
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Old 10-16-2019, 09:13 AM   #15
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It seems like small Diesel engines pushing big loads get worse mileage than big ones with tall gears and the same loads. My class eight tractor used to get 7 miles per gallon at a gross weight of 40,000 pounds (I was always lightly loaded) The tractor running down the road by itself could get 14 miles per gallon. Makes me think that if you could stuff a 14 liter semi-truck engine into a bus you could probably get 12 miles per gallon.
I had a friend give me an old caddy 472 motor. Took it out of a car to be used for demolition derby, he used chevy 305 for power. He said they hot started better than anything he could find. But that motor when into a 1 ton chevy. The old 350 got about 7 mpg. That caddy got 12. Ran in hard also.
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Old 10-16-2019, 09:26 AM   #16
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well makes me feel good that my old gasser is getting 6mpg consistently.

You can measure the length, width, height of your fuel tank and calculate cubic inchs, divide by 231 to get gallons.

edelbrock 1405 tuned a little bit lean on the primaries.. (I can richen the mixture slightly with the manual choke if needbe). the 392 seems to be more efficient running slightly lean vs rich on the primaries but likes it rich when the secondaries open.
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Old 10-17-2019, 10:43 AM   #17
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Engine: CAT C7 300hp w/retarder
Rated Cap: 46 + 1 36,200 lbs
Quote:
Originally Posted by EastCoastCB View Post

Are you SURE you have a "300 hp" C7 variant? Most school buses have 170-230 hp ratings. The higher rated C7's have several differences to the lower rated ones. I have a 190hp 3126 and the highest I can rerate is to 210.
I'm getting at least 10 mpg in my 5 window shorty but it doesn't have typical school bus gearing. Its 3.42 and it does great on the interstate. Even has the lamented 545 transmission.
The C7 in this bus has the engine brake which only came with the high horsepower versions. It was used to transport basketball and football players for a high school in eastern Colorado. It seems to have been purposely spec’d out to run long highway miles in an area of the country where the distances between towns is great and the country is wide open. It also has an Allison 3000 transmission with six forward gears available. Unfortunately the build sticker is blank where the information for the rear axle ratio would normally be found. I can tell you this though, when I am rolling at 75 miles an hour the engine is turning 2200 rpm’s. When I was in western Kansas on US Highway 50 a couple of days ago I encountered rolling Hills with what I would estimate to be 2% - 3% grades. At those sections there was a slow lane for the trucks and a passing lane on the uphill side of the road. In those spots I was able to stay in the passing lane and I lost only 3 to 5 mph from my cruising speed. I am hoping this engine can be re-rated to 360 hp.

Also, notice the designation on the sticker where it indicates information about the engine (see attached image).

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Old 10-17-2019, 10:55 AM   #18
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Originally Posted by wrenchtech View Post
It seems like small Diesel engines pushing big loads get worse mileage than big ones with tall gears and the same loads. My class eight tractor used to get 7 miles per gallon at a gross weight of 40,000 pounds (I was always lightly loaded) The tractor running down the road by itself could get 14 miles per gallon. Makes me think that if you could stuff a 14 liter semi-truck engine into a bus you could probably get 12 miles per gallon.
My Bluebird with the 8.3 gets 9-10.5mpg with mostly highway driving.

My Eagle, with the 8v71 and weighing 43k pounds, got a consistent 7.25 mpg.
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Old 10-17-2019, 11:24 AM   #19
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Peak power output on the 3126 engine that preceded the C7 was at 2200 RPM. If the same is true of the C7, then my bus was made to cruise 75 miles an hour, because that is the engine rpm I have observed running at that speed. I was worried that at 2200 rpm the engine was turning too too fast. Apparently it is right in the sweet spot at that road speed.
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Old 10-17-2019, 11:40 AM   #20
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My Bluebird with the 8.3 gets 9-10.5mpg with mostly highway driving.

My Eagle, with the 8v71 and weighing 43k pounds, got a consistent 7.25 mpg.
The best fuel mileage that I was able to observe on my recent trip was 7.7 MPG. On one leg, where I covered 300 miles between fueling stops, I observed 7.4 MPG. This was all open highway driving using cruise control. Oh how sweet it would be to get 10 mpg! If I understand what Iíve been reading, many diesel engines that are under a strict emissions control regime, can have their fuel consumption improved significantly by re-programming the ECM. As the later C7 common rail engines begin to fall out of warranty, I am hoping that some reasonably priced aftermarket tuning services will be offered in the marketplace.
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