how big is my fuel tank

[Bryan]

Hey guys, so I've read that the 4107 came with a 140 gallon fuel tank. Because I don't have fuel gauges and I'm pulling some trailer weight, I'm trying to figure out a good mileage to know I can go before getting more fuel. I'm not sure how to tell if it is the original fuel tank. I'm not sure what the POs have done, but I do know that the generator tank is separated from the main tank even though it's all connected into the same big square box, I'm thinking there is a divider in it. Was it divided when it came from the factory originally? Maybe this is a new tank? Not sure. Thanks for any input.

[rgrauto]

Bryan my Mci5 has a 144 gal. fuel tank and no fuel gauge also. I made a dip-stick out of an broken band saw blade ground off the teeth, panted it black, to make the fuel show better and it works well. I dipped the tank,marked the stick and added 5 gal of fuel and it increased 3/4 of an inch on the stick so this gives you as estimate of how much fuel you have so guessing 5 to 8 mpg you can judge range. You can mark the stick and fill the tank and get an idea how much fuel in tank and mpg. when you re-fuel.  It's been said they re fueled these buses every five hundred miles ,but do check what is best for you. HTH,Glen

[B_K]

Well as you stated it's hard to tell what a PO has done.
But it's very unusual for a stock tank to be replaced with anything but stock.
That being said it's not entirely impossible that it might not have been replaced with a custom unit or even the stock one customized.

What is VERY unusual is if it's just on tank divided into 2 separate tanks.  

Now how do you fill the generator part? Are there separate filler caps?

If it's just one cap then it's not a separate tank and what most likely has been done and wrongfully described as "separate tanks" is that they will a lot of times install a fuel pick up tube for the generator in the main tank but limit the amount of fuel it can draw by keeping it up 6", 8", 10" etc off the bottom of the tank so that the generator doesn't cause you to run out of fuel for the engine while sitting parked somewhere and using the generator.

Now I don't know ANYTHING about GM's and even less about 4107's so I can't even begin to tell you about what size tank you have or even how the neck is configured. But what I do know is an almost guaranteed full gauge that works on most trucks and buses is a fuel stick or hose! (if the neck bends and a stiff stick won't make the curve a semi-flimsy hose with a weight of some kind on the end works well to drop in the tank until it bottoms out and then pull it out an see how much fuel you have in inches. Then compare that to the depth of the tank in inches.

Another good way of doing it is to just be sure and fuel every so many miles regardless of what size tank you have and soon enough you'll have a good idea how far you can go. Most people use 400-500 miles as a starting point and adjust from there.
 BK  

[Bryan]

Thanks guys! There are definitely 2 places to put in fuel (one on one side of bus, and one on the other) there is also 2 drains underneath the tank, but it is one long tank.

[Oonrahnjay]

...  what I do know is an almost guaranteed full gauge that works on most trucks and buses is a fuel stick or hose! (if the neck bends and a stiff stick won't make the curve a semi-flimsy hose with a weight of some kind on the end works well to drop in the tank until it bottoms out and then pull it out an see how much fuel you have in inches. Then compare that to the depth of the tank in inches.

      Good points, there, BK.   I'd add that most tanks have the pickup a "little" off the bottom so it doesn't pick up trash and water off the very bottom of the tank.  Also, if there's a pinhole or broken piece at the bottom of the pickup, it will leave more fuel in the bottom of the tank when you use all your "useable fuel".  To be really sure, you should pump out your tank into a can (prolly real good to start when you're near empty anyway) then measure from what's your "minimum pickup" level -- but I don't have the patience for that and I can't imagine most people doing it.  But just saying ...
      I like your flimsy-hose idea but I have found that a cut-off remainder of Romex is good.  It will take markings with a permanent pen pretty well, or you can scratch graduations in it as you measure.  And it's flexible but it also "take a set" if you need to bend a curve in it.  Of course, like most other things - nothing works on ALL buses.
      HTH,  BH   NC

[MightyThor]

Grampa always told me it's just as easy to keep the top half of the tank full as it is to keep the bottom half full.  With a full tank you can easily determine your exact MPG cause you fill it to the same spot (full) and then drive x amount of miles then fill it again and see how many gallons it took you to drive that far.  once you have that, you can roughly calculate how far you can go for any given amount of fuel.  And, as the others have said, you can get a fair idea of the tank size by adding a known amount of fuel and then measuring the increase in the level on the dip stick.  if 10 gallons equals 1/2 inch, then 6 inches of fuel should be roughly 120 gallons.  This assumes a symmetrical tank.  If you got bumps or humps it can change things.  

[Bryan]

this whole thing brings up another issue I have been having. My generator which only has 400 hours on it seems to randomly try to bog down. I notice it when I top hills or lean to the side, but the gas can be completely full when this happens. I also notice it kind of changing tones from time to time while sitting still like it's getting just a little less gas at times. thanks for your input.

[Oonrahnjay]

this whole thing brings up another issue I have been having. My generator which only has 400 hours on it seems to randomly try to bog down. I notice it when I top hills or lean to the side, but the gas can be completely full when this happens. I also notice it kind of changing tones from time to time while sitting still like it's getting just a little less gas at times. thanks for your input.

     It would sure help to know the configuration of your generator fuel pickup.  That's the location of the pickup point in the tank (left/right and front/rear) and height above the bottom.  It *could* be that the sloshing of fuel is starving the generator.  But when you say "can be completely full" that makes if unlikely.

[HB of CJ]

We usually stopped every so often to get out and stretch our legs, plus walk and clean up after our two 5 pound small killer attack dogs.   Before we would leave on our trips, we would plot out what we wanted to see, what we may want to see, where to stop and either make lunch or where to eat at some untried restaurant.  We tried never to run out more than half a fuel tank.  When we could, we would stop at a gas station and sometime top off the tanks so we would have enough to get back home.  Just us.

Had a gas gage, but it did not work.  So I measured the fuel tanks and then figured out a reason net fuel capacity.  Experience gave us our fuel consumption rate.  The rest was easy.  We made frequent fuel stops along with all the other stops.  This took a slight burden of paranoia off my shoulders and made for a more fun trip.  We always knew how much fuel and water we had left.  We used a broom stick handle.  Also used it for the water tanks at first.  Worked just fine.  We did fix that pesky gas gage.

HB of CJ (old coot) 1974 Crown Supercoach 40 foot 10 wheeler ex schoolie.  VIN 37317 Sadly sold.   SW OR USA