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Old 07-26-2014, 11:37 PM   #1
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Pleasant Surprise!

Did my first MPG Calc. on our new to us 07 Discovery. 9 MPG not even factoring in about 4 gallons to the genset. That's even towing the 05 Jeep Grand Cherokee! 330hp CAT C7 rocks!
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Old 07-26-2014, 11:39 PM   #2
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Quote:
Originally Posted by mchero View Post
Did my first MPG Calc. on our new to us 07 Discovery. 9 MPG not even factoring in about 4 gallons to the genset. That's even towing the 05 Jeep Grand Cherokee! 330hp CAT C7 rocks!
How did you exclude the gallons to the generator....
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Old 07-27-2014, 01:57 AM   #3
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Seriously, flagship?

Note your generator Hobbs time at each fueling, and deduct your gen fuel burn for that time from the total fuel purchased. That accounts for your generator burn from that last tank, and the remaining amount that you bought is your net fuel to engine. *That* is the fuel quantity you use to calculate your mpg.
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Old 07-27-2014, 03:45 AM   #4
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congratulations!

best of luck and many happy journeys in your "new" rig
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Old 07-27-2014, 07:10 AM   #5
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Now you have a base number. I have kept a list of each fill up, and miles per tank. It is interesting, but jumps all over the chart due to speed, wind, which towed vehicle, route, and generator run time.

Easiest for me, is Diesel is likely to be around $4.00, and mileage is likely to be hopefully 8mpg. So $ .50 per mile, or dollars for the trip equal the number of miles outbound. So far, we are still driving and loving the RV experience, and not surprised. Having a 150 gallon tank allows for us to watch fuel prices on Gas Buddy, and make smarter purchases, often saving .10 or more per fill up. Still that savings in less than a Subway comb meal.
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Old 07-27-2014, 07:23 AM   #6
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Sailwing--I like your math! Instead of MPG, $PM.
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Old 07-27-2014, 08:32 AM   #7
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MCHERO, congratulations on your MPG, how many gallons per hour did you allocate to your generator? I would sure be happy with those results although it still isn't cheap to move these things around the country.

I also use the outbound math method and it works really well for estimating the fuel cost for a trip. If we want to spend a couple of days somewhere, I check the mileage to get there and that is the cost of fuel for the round trip. From our house to the grandkids is 228 miles so that hug and smile from our granddaughter cost $228 but is so well worth it and I don't have to burn up too many brain cells to figure out how much of a ding it will take out of our fuel budget.

Does anyone else get 9 MPG, that seems pretty strong to me and my results. Although, I readily admit I haven't even got 1,000 on our new to us RV, I don't anticipate even getting an average of 8 but am hoping for over 7 somewhere and with the generator running our overall fuel cost is going to be right at that 50 cents a mile no matter how hard we try to improve our actual MPG.

We had our last DP for 8 years and averaged just under 7 mpg and the 50 cent rule was right on track generally.
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Old 07-27-2014, 08:50 AM   #8
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Mine runs between 9.3 and 10.3 MPG depending on head winds.
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Old 07-27-2014, 09:08 AM   #9
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I'm jealous, mchero! That's great MPG for a MH. Congrats! \ken
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Old 07-27-2014, 09:16 AM   #10
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Thanks all, as stated in the above post I did NOT even factor in the generator tun time. 7.5kw quiet diese. What's the avg. burn rate under med load?
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Old 07-27-2014, 09:43 AM   #11
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Thanks all, as stated in the above post I did NOT even factor in the generator tun time. 7.5kw quiet diese. What's the avg. burn rate under med load?
I've got an Onan 7.5 also. I use 0.6gph as a constant figure, and it seems to work out for me. Perhaps it ought to be a bit higher, but not over 0.7 as an average.

With that number I've averaged 7.4 mpg (actual fuel to engine) over the last 2 years/15K miles. With toad, I'm running at just about 35K lbs-- a little bit over the 100lb per hp rule of thumb.

I don't think I've driven my coach more than a hundred miles total without the toad attached. When loaded up near the max, how sensitive is the engine to total weight? Would running without a 4000 lb toad make a huge difference in mpg?
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Old 07-27-2014, 09:54 AM   #12
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Over 55,567 miles average is 10.196 MPG.
LP generator. All fuel bought is on a spreadsheet to get actual MPG.

All miles pulling a toad of some kind.

Average has went down some the last couple years when Bio has been added at some stations and more all the time.
But Bio is a good added lubricant.
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Old 07-27-2014, 09:55 AM   #13
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Originally Posted by JFXG View Post
Seriously, flagship?

Note your generator Hobbs time at each fueling, and deduct your gen fuel burn for that time from the total fuel purchased. That accounts for your generator burn from that last tank, and the remaining amount that you bought is your net fuel to engine. *That* is the fuel quantity you use to calculate your mpg.
Yes seriously - I don't pay any more attention to MPG than what my computer tells me and what my brain tells me relative to the driving conditions I experienced. This is enough to give some comfort as to how the engine is performing.

As for using the *book* estimated burn for generator hour - I have no idea if my generator operates at that level of efficiency - what are talking about anyway ----> 0.4 - 0.5 an hour - @ what load etc. Maybe I need to set up a benchmarking of my 8KW Onan performance to published table values and develop my burn ratio conversion factor by fuel grade, altitude and temp for each state.

I haven't *sticked* an in ground fuel tank since I worked in a gas station as a kid - and learned that some haluers would bounce the stick to get the inches mark higher on the stick. I also have no idea when I fill up if the fuel came up to the same point cause I don't want it sloshing out on my pretty paint. Usually around the second burp I stop. I also don't have temperature conversion charts to determine if the fuel that went in at 45 degrees in the morning and was consumed at 80 degrees had volume changes (heck not even sure if diesel volume changes with temp. ) I do know that when I worked in the gas business buying 8,000 gallons at a time there were big differences in gallons pulled at terminal and dropped at station due temps at drop.

The coach isn't going to move without fuel. I have no control over fuel prices and I am not going to let fuel price / consumption dictate our journey.

So for me I am more concerned with whether my engine is performing within the expected range given the circumstances - than what the cost or performance *appears* to be based on a generator manufactures table and one I have to keep up with. The onboard computer and a glance at the metered gallons to gauge reading is good enough for me. I don't like pumping fuel in the first place - all of this makes it less enjoyable to me.

I'm curious as to how many decimal points fuel watchers carry this exercise out to - 5 maybe 6 places. I can hear the stick bounce now.... The whole thing presumes a level of accuracy and precision beyond the range of the data IMHO - YMMV and does, and will, and then what?

I propose a toast: May the OP and all of us always have more than enough money to keep our tanks full and may our generators and engines be trouble free and operate at top efficiency.

RVM2
Steve and Annie
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Old 07-27-2014, 11:24 AM   #14
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Originally Posted by flaggship1 View Post
Yes seriously - I don't pay any more attention to MPG than what my computer tells me and what my brain tells me relative to the driving conditions I experienced. This is enough to give some comfort as to how the engine is performing.

As for using the *book* estimated burn for generator hour - I have no idea if my generator operates at that level of efficiency - what are talking about anyway ----> 0.4 - 0.5 an hour - @ what load etc. Maybe I need to set up a benchmarking of my 8KW Onan performance to published table values and develop my burn ratio conversion factor by fuel grade, altitude and temp for each state.

I haven't *sticked* an in ground fuel tank since I worked in a gas station as a kid - and learned that some haluers would bounce the stick to get the inches mark higher on the stick. I also have no idea when I fill up if the fuel came up to the same point cause I don't want it sloshing out on my pretty paint. Usually around the second burp I stop. I also don't have temperature conversion charts to determine if the fuel that went in at 45 degrees in the morning and was consumed at 80 degrees had volume changes (heck not even sure if diesel volume changes with temp. ) I do know that when I worked in the gas business buying 8,000 gallons at a time there were big differences in gallons pulled at terminal and dropped at station due temps at drop.

The coach isn't going to move without fuel. I have no control over fuel prices and I am not going to let fuel price / consumption dictate our journey.

So for me I am more concerned with whether my engine is performing within the expected range given the circumstances - than what the cost or performance *appears* to be based on a generator manufactures table and one I have to keep up with. The onboard computer and a glance at the metered gallons to gauge reading is good enough for me. I don't like pumping fuel in the first place - all of this makes it less enjoyable to me.

I'm curious as to how many decimal points fuel watchers carry this exercise out to - 5 maybe 6 places. I can hear the stick bounce now.... The whole thing presumes a level of accuracy and precision beyond the range of the data IMHO - YMMV and does, and will, and then what?

I propose a toast: May the OP and all of us always have more than enough money to keep our tanks full and may our generators and engines be trouble free and operate at top efficiency.

RVM2
Steve and Annie
Hi Steve....... You asked, and I answered. Then you wrote seven paragraphs about how you really don't care in the first place. Whatever.
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