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Old 11-29-2020, 08:00 PM   #1
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Another question on fuel economy

Hi all,

Being a newbie on here I'm not sure if this is the right spot to post this question but I didn't see a spot that looked more appropriate, so here goes...

I'm going to buy a used diesel pusher and have a question about how the weight of the rig will affect fuel economy. I haven't found that "perfect RV" yet and that's why I can't supply any more detail. Let's consider two different Class A's and you tell me what you think the average mpg will be for each. Now this assumes that both are driven by the same person over relatively flat land with a few small hills and driven at about the same speeds and the same wind conditions.

Coach #1 is a 35' diesel pusher with a Cummins 300 hp engine and an approxmate weight of around 35,000 pounds.

Coach #2 is a 38' diesel pusher with a Cummins 350 hp engine and an approximate weight of around 41,000 pounds.

OK, you RV'ers with much more experience than I have (which is ZERO!) what would be the approximate mpg for each of those?
2008 Monaco Cayman XL 35'
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Old 11-29-2020, 08:15 PM   #2
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8-9 mpg

If you are concerned with MPG and might not want to RV

They are a 'hobby' to be used for enjoyment
BUT they are big boxes on wheels and mileage suffers from lack of aerodynamics more so then how much they weigh
And as a 'hobby' they cost $$$ to operate, maintain, repair, service etc

Fuel, tires and routine service cost $$$
Is it time for YOUR Medication or Mine?
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Old 11-29-2020, 08:27 PM   #3
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We have an old Motorhome...1996 ford 460.
I get about 8.4 to 9.1 mpg with it with the cruise on 60...
when towing the pickup we get about 7.5 mph / We'll un-hook and drive it over any mountain passes.
I found out the hard way if you want to go fast you're going to pay for it!

Where any RV get expense is the maintenance , try to do as much as you can.
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Old 11-29-2020, 08:31 PM   #4
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There are a lot of variable involved. For instance my RV gets between 9 and 10 in your example. I had a 2005 Winnebago with a cat 350 hp and got about 8 and that was about 37 ft long. Some of the newer rigs get better MPG with the DEF.

The other variable that affect mpg is how fast you drive. That will change the mpg rapidly the faster you travel. I generally don't drive over 65.
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Old 11-29-2020, 08:32 PM   #5
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Weight is probably secondary in MPG for a Class A. The big killer is the large blunt front end and overall air drag across the outside surfaces. IMO, the added HP of the larger unit is more than enough to handle the extra weight. MPG is usually between bad to poor in these rigs.
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Old 11-29-2020, 09:24 PM   #6
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Budget your trips for 8MPG and go out to dinner with what you have left over when the trip is over.
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Old 11-29-2020, 09:32 PM   #7
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My '02 Dutch Star with Cummins ISC 350/1050 with Banks kit (435/1200) got about 8 mpg towing a Honda Odyssey. The MH weighed 34,000, and the Ody another 4,500.
Present rig is a Cummins ISX 650/1950 towing a Keep Wrangler. MH weighs 62,000#'s and the Jeep about 4,700#'s. Overall mileage with it is 7.7 mpg.
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Old 11-30-2020, 11:06 AM   #8
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That's kind of what I figured, about 8-9. And no, I'm not worried about the cost of fuel, just curious. We have a boat that's on the market right now for $250. In anticipation of it selling fairly early in the spring I'm looking on RVTrader to find that perfect RV. And talk about a diesel hog, that thing gets about .8-1.0 mpg.

I keep bouncing back and forth in my mind about buying one in the ~38' size to maximize comfort (the boat we're selling is 55') so we don't have to give up a lot of creature comforts, or going with a 35' and sacrificing some of the stuff we've come to enjoy.

While this will be the first motorhome we've owned, we did traiiler a bit many years ago when the kids were little. Also, driving the bigger rig on't be an issue--I have my CDL with a 40' bus endorsement. I drove for one of the local school districts as a sub and absolutely loved it. If COVID were not in the picture I would still be shuttling those little darlings around.

Thanks for the replies and the information.

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Old 11-30-2020, 11:14 AM   #9
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For the FACTS on MPG vs speed and weight:

Basically weight is NOT a critical factor on flat ground.

It IS a significant factor on grades.

So, the answer to the OP's question is that it depends on where you drive.
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Old 11-30-2020, 12:38 PM   #10
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Bottom line is the magic number is about 8mpg. unless you have a lead foot, ( read above 65mph ) that will cost you.
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Old 11-30-2020, 12:45 PM   #11
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first off you do not buy an rv thinking of fuel mileage.
second mileage will vairy on speed weather road and weight so it will be different from place to place driver to driver.
we ranged from 5mpg to 8.5mpg over 7000 miles over all 5.5 is what we got for the trip. plan on 5mpg be happy if you get better
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Old 11-30-2020, 01:17 PM   #12
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I'm with the 8-9 crowd, but will drop a little lower and say 7 - 9 with weight not really being a factor unless the engine is severely underpowered. Also like others have already said, speed will more than likely affect your MPG far more than weight (keep it below 65). Finally, there are many that will tell you how the need/desire to watch MPG means that you shouldn't be looking at RVs. Shrug that one off as there are several reasons to know your MPG. I always watch for baseline MPG changes in case it is a signal that something may need attention.
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Old 11-30-2020, 05:57 PM   #13
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Originally Posted by DeWat View Post
I always watch for baseline MPG changes in case it is a signal that something may need attention.
DeWat, that's what I was thinking. I am not a lead foot and keep the car just above 70 on the freeways.

You and I are thinking alike. Must be something about those of us on the same side of that thin blue line that gets us thinking alike!
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Old 12-13-2020, 09:23 AM   #14
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Originally Posted by Roy-c View Post
Bottom line is the magic number is about 8mpg. unless you have a lead foot, ( read above 65mph ) that will cost you.
Amen lol
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