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Old 10-24-2012, 09:08 PM   #1
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2014 31' Classic
2015 23' International
2013 25' FB International
Apache Junction , Arizona
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Mercedes ML320 CDI bringing International Serenity 25FB home

I left Airstream Los Angeles for the first trip, taking the unit to the Phoenix area on I-10 from San Grabriel. I set cruise at 55 mph and the speed remained constant on the level and climbing the mountains headed East bound. On the steeper hills, the transmission would downshift from 7th at 1650 rpm to 6th and the rpm would increase to 1850. If the hill was steep enough, then fifth gear would be used at 2150 rpm.

The trailer was probably loaded with 300 pounds of water, tools and stuff. The Hensley hitch added about 200 pounds to the hitch weight. The gross weight was probably around 6,000 pounds. The Hensley hitch settings ended up with a level trailer and TV.

The first leg of 160 miles generated 20.0 mpg. However there was 25 miles unladen due to a flat tire issue where the tailer was left at a location and the car was driven to a tire repair facility and return.

The second leg of 115.4 miles was more mountainous and I got 17.1 mpg. The last leg of 164.5 miles was basically mild climbs and descents and the mileage was 17.3 mpg. The car typically achieves 28 when running at 70 mph.

As it was an all night driving event due to the tire issue, I was constantly passed by the big trucks at higher speeds in Arizona (75 mph). In California, the 55 mph was cheerfully ignored by nearly all big rigs. One could feel the air pressure build up as the rigs came around, but the hitch controlled any sway activity. I ended up on the East edge of Phoenix around 4:30 am and took a couple of sunrise photos, one at the Walmart parking lot and the other with the Superstition Mountains as the backdrop.

Really happy with how the rig handled. I will not win the national drag races, but acceleration is better than I expected.

There are two photos taken this morning of the complete rig.
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Old 10-24-2012, 09:27 PM   #2
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I do admire the fuel mileage of rig like yours.
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1990 35' Silver Streak Sterling; 9k GVWR.
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Hensley Arrow. 9-cpm solo, 15-cpm towing
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Old 10-24-2012, 09:53 PM   #3
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1959 26' Overlander
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I'm happy to see the mpg numbers too. We towed a 17' Caravel for thousands of miles and got very close to the same mileage. We now have a 26' Overlander and saw the same type of mileage, although it is gutted right now. It seems like the mileage is dependent more on the size and shape of the trailer than the weight -- on flat ground anyway. I'll be curious to see how it changes with added weight.

Thanks for posting the CanAm pic of the hitch reinforcement. With the larger trailer, we'll have to do something like that ourselves.

BTW, ours is a 2007 CDI. Unfortunately, we are on our second transmission. We have been given advice to keep transmission temperatures low while towing and manually downshift while climbing hills to reduce torque on the tranny.
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Old 10-24-2012, 10:22 PM   #4
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" . . It seems like the mileage is dependent more on the size and shape of the trailer than the weight -- on flat ground anyway.

Aero resistance is far more important than weight. And not just for fuel mileage, but in all aspects of trailer towing performance.

How to record fuel mileage is more complicated than it may seem where vehicle spec, climate, terrain and driver skill are the major hurdles to account for. Within them are: specific routing, engine-on time, ambient temps, etc. A perfected mechanical baseline for both vehicles is paramount for accurate comparisons by one driver.

One can achieve higher mpg with a longer & heavier trailer for the same TV where aero concerns are addressed.

.

.
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1990 35' Silver Streak Sterling; 9k GVWR.
2004 DODGE Cummins 305/555; 6-manual; 9k GVWR.
Hensley Arrow. 9-cpm solo, 15-cpm towing
Sold: Silver Streak Model 3411
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