Re: 400 ISL vs 450 ISM mpg Reply #25 – November 19, 2014, 06:03:19 pm Mine regularly gets 9-10 mpg, but only while cruising on the flat and level without wind. Add in normal stopping, stopping, traffic, grades, wind, etc and the average drops to 8-8.5. The coach's lifetime average is right around 8. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #26 – November 19, 2014, 08:15:54 pm Quote from: Brad Metzger – November 19, 2014, 03:45:02 pm Cummins states that the ISM-- is the smallest engine they make that is rated as "heavy duty " all other engines smaller than that are rated medium duty . All things other than that being equal , it would have to be ISM for the long haul for me . Hard to beat power when you pull anything and much so in the mountains . Brad MetzgerThe ISL is also consider a heavy duty engine by Cummins. As stated: Cummins 2013 Heavy Duty Engine Lineup, ISX, ISL, ISB . You will find the ISL9 today in every firetruck across America most around town fleet trucks run ISL9. While the ISM is also a great engine, the ISL for the motorhome is a fine combination considering the weight we pull. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #27 – November 19, 2014, 08:19:56 pm In my opinion, fuel is the cheapest part of owning a nice MH, at least when you're using fuel you are also using the coach. I wish that I had time to use more fuel. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #28 – November 19, 2014, 10:31:43 pm Quote from: D.J. Osborn – November 19, 2014, 02:45:53 pmThat's not quite accurate. My U320 with a 400 hp M11 will shift into 6th gear at just over 55 MPH. Combine with the fact that it has a higher (lower numerically) rear axle ratio than would a U270 or U295 with an 8.3 liter engine and the result is that for a given highway speed the larger engine will run at a lower RPM and thus have about the same fuel economy as would a smaller engine spinning faster.Mine shifts in sixth at 54-55 also. Boring driving that slow.Engine computer says it averaged 7.8 for 100k miles Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #29 – November 20, 2014, 07:44:19 am Quote from: Caflashbob – November 19, 2014, 10:31:43 pmMine shifts in sixth at 54-55 also. Boring driving that slow.Engine computer says it averaged 7.8 for 100k milesWe completely agree with the "boring" statement! Our U320 feels as if it was designed to cruise at about 70 MPH. We even cruised for a few miles in Texas at the 80 MPH speed limit and it still felt great! We traveled our first several thousand miles at about 62 MPH, until my wife could no longer stand the boredom at that speed. (I was happy when she spoke up!) The coach is so smooth and comfortable that it just seems to put us to sleep at that speed. For whatever reason, 70 MPH just feels right!Surprisingly, even though everything says we should use more power and burn more fuel at 70 MPH, we haven't noticed any significant difference in fuel consumption. Even though I'm very careful to be consistent at each fuel fill, and keep detailed records, we remain at about the same MPG. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #30 – November 20, 2014, 07:53:08 am Yeah, we had the same result after Bernd tuned our M11.If I changed my 62mph to 70 the M11 just wanted to go 75.And I'd swear I got better mileage.best, paul Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #31 – November 20, 2014, 10:36:08 am I limit me excursions over 75mph, the tires' max rated speed, but have briefly been to 85 while passing, and the U295 handles like a dream there. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #32 – November 20, 2014, 12:51:44 pm Quote from: Paul Smith – November 20, 2014, 07:53:08 amYeah, we had the same result after Bernd tuned our M11.If I changed my 62mph to 70 the M11 just wanted to go 75.And I'd swear I got better mileage.best, paulThe engines best mpg is at 1500 rpm as far as I know Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #33 – November 20, 2014, 01:18:21 pm Quote from: Caflashbob – November 20, 2014, 12:51:44 pmThe engines best mpg is at 1500 rpm as far as I knowThat makes sense. At 70 MPH our M11 is turning just over 1500 RPM. It, and the rest of the coach, seem to be quite "happy" under those conditions. Therefore, so am I! Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #34 – November 20, 2014, 06:56:54 pm I think my M11 needs a tune, but no matter what speed we run, it gets 7MPG, anything from 60-75. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #35 – November 21, 2014, 01:28:23 am Quote from: wolfe10 – November 19, 2014, 02:30:22 pm That is one of the primary reasons a diesel is more efficient than a gasoline engine at partial throttle (other reasons include more BTU's per gallon, no throttle on the intake that creates a vacuum that the pistons have to pull against, etc).Higher compression ratio is usually the main reason...but everything you mentioned (and more) adds up. Quote Selected
Re: 400 ISL vs 450 ISM mpg Reply #36 – November 21, 2014, 01:35:24 am Quote from: Kemahjohn – November 20, 2014, 06:56:54 pmI think my M11 needs a tune, but no matter what speed we run, it gets 7MPG, anything from 60-75.No gen or Aqua hot use? Quote Selected
Topic: 400 ISL vs 450 ISM mpg