Community Forums

**Lt Dan** · 07-26-2019, 05:08 PM

Quote:

Originally Posted by tropical36

I must have a leak somewhere, with only 6.2 over a 12yr period, as indicated on the OEM diagnostics panel, being fed from the ECM. Still don't know if it's counting the genset consumption or not, but would hope so.

The ECM does not compute usage by the generator since it's a totally separate fuel system from the engine. The only accurate way to figure mileage is actual miles divided by gallons used over a number of fillups. For the generator usage, you can figure in 0.5-0.75 gallons per hour of use depending on the size of the genset.

tropical36 · 07-26-2019, 05:32 PM

Quote:

Originally Posted by Lt Dan

The ECM does not compute usage by the generator since it's a totally separate fuel system from the engine. The only accurate way to figure mileage is actual miles divided by gallons used over a number of fillups. For the generator usage, you can figure in 0.5-0.75 gallons per hour of use depending on the size of the genset.

Yeah for sure, but when I said ECM, I just assumed that is where the signal is coming from and can't hardly see where it could be coming from the fuel tank itself, so yes, mostly likely just the engine.
Genset is 7.5KW diesel and pretty much loaded with the ac's running in hot weather. In cool weather, we use the inverter, as much as possible.

tomgrigsby · 07-26-2019, 05:34 PM

Our Newmar 38 300HP Cummins seems to get around 8 or better, if taking it easy (less than 65 mph) I recently took a trip of 2600 miles and budgeted $900 for fuel but spent about $1,000. On the way out I limited my speed to 65 mph max. On the way back I went 70-75 mph and could tell that fuel burn definitely increased. RV travel isn't necessarily cheap, but it was sure nice to have all the facilities so lunches, bathroom breaks, etc. were so convenient.

LETMGROW · 07-26-2019, 05:37 PM

When I pull in for fuel I always buy a drink or two and a bag of snacks. It takes the edge off. I don't write the mileage or gallons down. I know I'm not driving a Prius so I just fill the tank and move along.
I used up all my bragging rights when I had my Isuzu pick up I bought new in 1986. I have always owned gas hogs. Cadillacs, Oldsmobiles, Chryslers and Big engine performance cars and large engine pick up trucks.
I had one John Deere tractor in my stable which burned 14 gallons of diesel in an hour at an idle. Didn't let it idle much and never went joy riding with it either.
My Pro Mod 700 triple cylinder race sled can use 5 gallons of race fuel in a day's racing. VP C-14 fuel is just over $90 per 5 gallon can.
Don't get hung up on mileage. You will forever be disappointed and become a liar when your friends ask you what you get for mileage with your house on wheels.
Lynn

asuperheat · 07-26-2019, 06:08 PM

My last RV was an Excursion 35B with the ISB. It was great I would get 9.2 pulling my Jeep, could get 10 with no towed.

Current RV Tour 42QD with the ISL appears to be around 7.5 with my jeep at 70-71 mph so far. Little over 8 with no towed same speed. Anything over 71 and the mpg drops fast on the new one. I get 7 mpg at 74 with the Jeep.

These are long distance highway numbers.

Team G · 07-26-2019, 06:23 PM

Quote:

Originally Posted by asuperheat

My last RV was an Excursion 35B with the ISB. It was great I would get 9.2 pulling my Jeep, could get 10 with no towed.

Current RV Tour 42QD with the ISL appears to be around 7.5 with my jeep at 70-71 mph so far. Little over 8 with no towed same speed. Anything over 71 and the mpg drops fast on the new one. I get 7 mpg at 74 with the Jeep.

These are long distance highway numbers.

43' tiffin bus 425 ISL cummins - running Gen. Travel +/- 70mph . 6.5 to 8 mpg. Variables of speed,terrain and wind account for range in mpg. Will eco the sentiment - 'didn't by it for milage'.

Tajfish · 07-26-2019, 06:32 PM

38’ diesel Bounder with 300 hp cat7. 6.2 is my lowest 8.1 is my highest. Windage and Elevation as the man said. It is a factor but don’t make it a big factor. It sure is nice to sleep in our own bed where ever we go

momdoc · 07-26-2019, 06:54 PM

We get about 8mpg on our 40 ft tiffin with toad. We also keep speed to 65mph or less.

JFXG · 07-26-2019, 08:25 PM

Too many variables to be very specific. As a general rule of thumb, if you’re moving about 100 Lb/hp you’ll get about 7.5-8 mpg, subject to speed, wind, terrain, gen use, etc.

**TonyDi** · 07-26-2019, 08:37 PM

I have a C-9 CAT in my MH and I am averaging 7-8 mpg. It's a bit lower if I'm in the mountains.

RiverBurt · 07-26-2019, 08:41 PM

It’s about half-way between you can’t afford it and you don’t care.

powerboatr · 07-26-2019, 09:05 PM

i used to track it...
but after years of a steady 7 - 7.5 i just click the IP read out to see if its changed.

i never ever look at instant mpg.

i use 7 as a marker when planning so i look for fuel in the range of 450-500 miles, this lets me run the genny almost all the time.

Ray,IN · 07-26-2019, 09:28 PM

This explains how speed vs wind resistance affects fuel mileage for cars: Mpg For Speed - Fuel Efficiency Vs. Speed
Now, use the drag coefficient for a rectangular box in that calculator. The results just may change your mind about your normal driving speed, IF you are concerned about fuel mileage. In todays motorhomes, the Cummins ISB seems to hold the best fuel mileage results. Our friends are at our house now, his 38' Winnebago Forza W/ ISB averages 10.6 MPH towing a GMC Colorado, per his log book. His normal highway speed is 58-60 MPH.

Crasher · 07-27-2019, 07:18 AM

MPG has a direct relationship to weight, wind resistance and speed. The wind resistance will be similar on all DP's, so the variables are weight and speed. If the speed is constant for comparison, then weight becomes the determining factor. One of my first DP's was a 39Z Bounder with a 275 hp ISB that weighed 28,500# loaded. 9-10 mpg was pretty common. Then I had a 40' Phaeton with a 330 CAT that weighed 32,000# loaded. It usually was in the 8-9 range. My current 43' Bus weighs 40,000# loaded and the 450 ISL will be 7 plus or minus most of the time towing a heavy toad. When I tow a 12,000# trailer, it's closer to 6 mpg than 7. It's a law of physics, as the weight of the RV increases, it requires more energy to push it down the road at any speed.