Community Forums

footdoc · 10-31-2006, 05:27 PM

My coach now has 3600 miles on it..when purchased it had 1500 and got right at 6.3 mpg with toad and dash air on. Today on a trip in the same driving conditions, except NO dash AC I got 7.3 ! Does dash ac pull 1 mpg or is the Cummins getting loose? also slightly cooler weather by about 15 degrees....mid 70s.

footdoc · 10-31-2006, 05:27 PM

My coach now has 3600 miles on it..when purchased it had 1500 and got right at 6.3 mpg with toad and dash air on. Today on a trip in the same driving conditions, except NO dash AC I got 7.3 ! Does dash ac pull 1 mpg or is the Cummins getting loose? also slightly cooler weather by about 15 degrees....mid 70s.

Lug_Nut · 10-31-2006, 05:42 PM

Larry, Cooler weather actually decreases fuel economy due to denser air. I doubt the engine would loosen up that quickly, try about 20k or more. More than lightly it was due to wind condition differences from one reading to the next. Speed is the biggest affect on consumption and this is mainly due to wind resistance, though of course there is more factors. Even a 10 MPH wind against you as apposed to behind you will make a wooping difference.

footdoc · 11-01-2006, 02:44 AM

Hi Nut...
I understand all about temperature, etc. Actually cooler air increases power output because it is denser...that is why intercoolers are used with turbo setups. Wind wasnt a factor in either measurement....about the same, BUT speed was..I was actually running about 66 instead of the usual 63 for me..Maybe my triptek is wacky? Makes me feel good showing 1 mpg better tho

Lug_Nut · 11-01-2006, 03:05 AM

Larry, you may not be far from the answer thinking the TripTek may be somewhat inaccurate. I use TripTek on this and my last coach and I've made an observation. Do you ever notice the fuel milage always seems poorest when you first start out in the morning and seems to improve later in the day? My both have. I'm wondering if fuel temperature does not affect the reading. The fuel warms as the fuel return line feeds unused fuel back to the tank at considerably a warmer temperature than it left the tank. I found my last TripTek, on my DSDP, to be averagely 7% inaccurate showing that as lower than real MPG.
Just a thought.

footdoc · 11-01-2006, 03:14 AM

I havent taken enough trips to even notice that. I also have not tried the old fashioned way of measuring the actual fuel used from fillup to fillup...kind of tough to do with foamy diesel..gotta go slow....will try that next vs the triptek info..thanks

Toterman (David) · 11-01-2006, 01:59 PM

I have found that this time of the year you will start running into the winter mix fuel in some parts of the country and that has made about half mile per gal to one mile per gal difference in my toter. But it is less per gal not more.

David

Lug_Nut · 11-02-2006, 06:18 PM

David, That's a good thought. The winter grade fuel would explain a lot and you never really know what your getting at some stations during some times of the year. I wonder if winter grade's gravity weight is diffent than regular summer grade #2. If it were milage may vary as the tank empties.

Brigadoon · 11-04-2006, 04:46 AM

I check my mileage often. I do it the old fashioned way by filling up the fuel to the same point in the filler neck each time. The wife reads her book while I do this since it takes time to overcome the foaming. I cross check the actual miles driven with the odometer and my gps. They are close in their reported mileage.

When my ISL had about 5k miles on it we took a 6k mile trip and discovered that my overal mileage was 7.3 mpg. The low was 6.7 when running the generator and both house airs and a high of 7.9 not running the generator and driving about 60 mph.

This year, with 15k miles on the engine, we took another 5k mile trip and averaged 7.9 mpg overall. The low was 7.0 running the genny and the airs and a one tank high of 8.05 mpg. Most of the time we averaged 7.94-7.97 mpg. I almost always drive in the 62-65 mph range. Beside the increased break-in mileage on the engine, I had changed the engine oil to Amsoil. I don't know if that has any actual effect, but I figured it doesn't hurt.

heybc · 11-05-2006, 04:07 AM

Our coach had 9K on it when we bought it. First milage check was 7mpg. We slowed down to 55-60 MPH and the milage increased to 8-8.5. This last trip has varied from 7.5 in the mountains in the west to 8.5 in the plains. We are happy with that in a 32K coach pulling a 4K toad.

clubmed98 · 11-05-2006, 01:04 PM

engine reps have indicated some power loss in new cleaner fuel..just a thought and probably not that important but the change to new ultra low sulfer fuel may have an effect

Ecker · 11-05-2006, 01:50 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Str8Shooter:
I check my mileage often. I do it the old fashioned way by filling up the fuel to the same point in the filler neck each time. The wife reads her book while I do this since it takes time to overcome the foaming. I cross check the actual miles driven with the odometer and my gps. They are close in their reported mileage.

When my ISL had about 5k miles on it we took a 6k mile trip and discovered that my overal mileage was 7.3 mpg. The low was 6.7 when running the generator and both house airs and a high of 7.9 not running the generator and driving about 60 mph.

This year, with 15k miles on the engine, we took another 5k mile trip and averaged 7.9 mpg overall. The low was 7.0 running the genny and the airs and a one tank high of 8.05 mpg. Most of the time we averaged 7.94-7.97 mpg. I almost always drive in the 62-65 mph range. Beside the increased break-in mileage on the engine, I had changed the engine oil to Amsoil. I don't know if that has any actual effect, but I figured it doesn't hurt. </div></BLOCKQUOTE>

Oil doesn't make any difference but wearing down the tires does -best mileage comes when their at 50% of tread and of course the engine itself which probably needs at least 20,000 miles. Fuel will vary with weather i.e. winter mix will get less - ULSD will proably vary by engine maker more than the fuel per se. Most important is speed since its a cubed function.

cwg · 11-05-2006, 03:21 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Oil doesn't make any difference but wearing down the tires does -best mileage comes when their at 50% of tread and of course the engine itself which probably needs at least 20,000 miles </div></BLOCKQUOTE>

Attending a seminar the Cummins factory rep teaching stated " the engine is considered wet {translated: not broken in} until an average of 28,000 miles." Sure seems like a lot of miles to me, but it sure gives hope to those hoping to squeeze out a few more miles per gallon as the engine wears in.

tmitchell · 11-05-2006, 04:23 PM

I took off on my first long trip of approx. 5,000 when my 370 HP ISL had only 2,000 miles on it.
Since than I have taken 3 more long trips of between 4,000 to 5,000 miles a piece, I now have 31,000 miles on the MH.
My first trip averaged 8.6 MPG my last 3 long trips averaged basically the same. I only check my milage on long trips so I can get a more accurate reading.
I am more than satisfied with the mileage to date, but I have seen no indication of the engine braking in and my mileage increasing.