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Old 02-17-2015, 09:25 PM   #15
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Corpus Christi , Texas
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Uphill MPG and speed

I may hit the grade harder than my normal travel speed. Suspend the cruise control. I expect to fall back in speed depending on ascent percentage and distance. As well at least one gear on the manual transmission.

Ascent speed is relatively meaningless. It is the descent that matters. I can hardly see a good reason to arrive at the top and to have to slow for the proper descent speed. Chances are that I am already near to that speed as well as the proper gear with above way of doing things.

I will say that anyone using CC on a steep ascent is none too bright. The speed differential between vehicles widens. Nothing quite so stupid as four wheelers piling up behind slower vehicles.

Separation distance is just possibly MORE important now than ever.

As to fuel burn, there is no good reason, again, to ask the motor for more than is needed. Speed matters not, but braking and evasion distance does. Fuel burn, thus temps, will take care of themselves when emphasizing defensive driving on an ascent . . the all important descent is just ahead.

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Old 02-18-2015, 12:57 AM   #16
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Snoqualmie , Washington
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I do the speed limit or 5 over, up to 65 mph. With a Cummins diesel, power is not a problem and the revs rarely exceed 2000rpm. A really long pass with a steep grade will make the oil and transmission temps creep up a tad, but never in unfavorable ranges. Gas mileage suffers, but it is usually redeemed on the downhill run, using exhaust brake to help regulate speed.

Most often I am passing tractor trailers and gas powered RV's.

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Old 02-18-2015, 06:25 AM   #17
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Arvada , Colorado
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With our earlier 2008 Suburban 2500 we generally traveled at 65 mph on the flats and experienced about 10 mpg. In the hills we kept the rpm's below 3000 and whatever gear was needed. More than once out west we experienced a 1st gear climb at about 4 mpg. I don't think you indicated what your tv is, but gassers really suffer at higher altitude. I'm told a horsepower loss of 3% per 1,000 feet in altitude.

All this is said given the fact that we recently got rid of the 'Burb in favor of a Silverado 2500 HD Duramax. We expect a much better driving season - rpm's, mph, and mpg - this year
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Old 02-18-2015, 07:27 AM   #18
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Petaluma , California
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I manage the speed limit (55-60) until my Pyrometer reaches 1000 degrees then I manage gear and speed to keep the exhaust gases under 1100 degrees and Tranny oil temp under 200. (2002 7.3 powerstroke with DPTuner +80HP, 15,000 lbs GW trailer and truck). I can usually hold 50 easily but tend to go a little slower if trucks in the granny gear lane are going under 30. I don't like traveling in adjacent lanes at more than a 20MPH differential as trucks can sometimes pop over a lane to avoid losing inertia when coming up on a heavily laden 10MPH truck and if you are barreling up the hill in an adjacent lane you won't have a lot of time to react. An extra 15-20 minutes to make the grade so to speak never hurt anyone and you need to slow down going down the other side anyway.

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Old 02-18-2015, 07:42 AM   #19
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Los Angeles , California
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I tow at 60, and on a 2:45 hour drive from Pasadena to Central coast of California I average 18 mpg. Its 18.5 until the climb between Santa Barbara and Buellton. I tow the climb at 60 in 5th gear. The temps don't budge on our 2014 VW Touareg TDI. I'm able to tow it at 65, same gear but then I miss the scenery
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Old 02-18-2015, 10:17 AM   #20
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San Jose via Winnepeg, Toronto, Orlando, Saratoga and Groton , California
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I tow at 55 which is the law in CA for vehicles while towing; uphill on gentle climbs on intersates I try to maintain 55 but realize the mountain wins and its important to watch the transmission oil temp and coolant temp. Going over passes near 9600' I end up just crawling up the hill above 8000' in first gear - like on Sonora Pass in CA. On the other side controlling the rig speed without using brakes and so I'll be in 1st gear and top out about 20 - the turns also don't allow me much speed either.

Interestingly, although the physics says I should make up the poor gas mileage on the downslope, the mpg in the computer never recovers after going through a pass. Some kind of paradox that's probably explainable with a look into the math...
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Old 02-18-2015, 11:17 AM   #21
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Hot Springs , Arkansas
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Go easy on the RPM's, Don't lug the engine and trans. Enjoy the drive, and wave with a BIG SMILE when people pass you.
I get 12-14 in our Yukon, and 6-10 with my big truck. I personally don't care about mileage when I pull mine. Im just having too much fun to rent out space to worry.
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Old 02-18-2015, 11:40 AM   #22
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I watch turbocharger EGT, water temperature, transmission oil temperature and rear differential oil temperature as we typically maintain posted or 65 maximum speed on interstates. The lie-o-meter can show around five mpg. The critical number is to not exceed 1250 degrees on the EGT gage to keep from damaging the turbine wheel or housing of the turbocharger.

We see around 13 to 13.5 mpg on the flats. I plan my range based upon 11 mpg and that is a range over 600 miles on the 56 gallon tank.
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Old 02-18-2015, 12:06 PM   #23
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Penokee , Kansas
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Hard pulling I lock my trans in 4th gear if I can.. Reason,, 4th on my pu is direct and the power flows in and out without any clutch packs turning.. With that along with my 4-1 gearing limits me between 50 and 65 mph.. I monitor my engine load gauge more than anything as I don't like to apply anything over 75% POWER for any given RPMs.. I do ck the trans temp,, and engine temp,, but have never had it out of normal range ever..

On a real hard pull that 4th cant keep up I will drop down to 2nd and float the power at or under that 75% power setting..

No engine has been made to pull at 100% power for any constant amount of time.. Anyway not if you wish to see 350,000 miles life out of it..

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Old 02-18-2015, 12:33 PM   #24
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When I tow my 26' Argosy with my '08 Tundra. I put the transmission in the "S" mode and select 4th gear as the highest. On rare occasion I will shift up to 5th until the transmission starts shifting back and forth because of terrain or wind etc. then it's back to 4th.
The fuel mileage is 12.5 to 14mpg. The lower end is due to mountain driving in the Colorado Rockies.

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Old 02-18-2015, 12:36 PM   #25
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On the flats you are fighting rolling resistance and wind resistance only. Wind resistance increases exponentially with speed so slowing down helps with that. Climbing adds a fixed load of work to the equation. The amount needed to get up the hill. The formula for this is the weight of your rig times the increase in elevation. Fast or slow it is the same. Faster is obviously putting a greater strain on your machinery. For gassers find a gear that lets you keep the rpms between 2500 and 3500 and watch the temperature gauges. Diesel rpms will be lower. If it starts to cook you are working it too hard. Slow down and use a lower gear. Your fuel use will be a sum of miles per gallon plus gallons per 1000' of elevation gained.
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Old 02-18-2015, 01:26 PM   #26
2014 27' FB Classic
Katy , Texas
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Always Take It Easy

We're full-timers in high travel mode and make it a point not to be in a hurry to get anywhere. This allows us to focus on prolonging the useful life of our 2007 Tundra and maximizing MPG. We tow with the tow control on and just plain take it easy. In the flats, this means 60 MPH maximum speed at 2000 rpm or less; in the hills and mountains, we let the Tundra 'find its own speed' and try not to exceed 3000 rpm. If necessary, we'll take the same approach using the manual shifting for the steepest inclines. The Tundra can do much more than we've been asking it to do. So far, our strategy seems to be working just fine - no major repairs first 15 months travelling to 35+ states. Time will tell.
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Old 02-18-2015, 02:06 PM   #27
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I wonder if the reason you're not getting good mileage downhill is that you're going down in first gear. When we towed our 28' International with our 4 speed 3/4 ton Suburban 2000, 2nd gear held us pretty well down those same slopes. I did use braking, however--set the trailer brakes a bit more aggressively than on the level, and (as long as traffic allowed) would use changes in terrain and/or light and not prolonged braking to take our speed down to 45, and then come off the brakes until we hit about 55-60, then reapply and repeat. Got great mileage downhill this way, and never had a problem with brakes.

Now that we tow with the Sprinter 3500, we do the same thing. The Sprinter brakes seem to be much more substantial than the Suburban's. But again, 2nd gear gives us a much better cursing speed and substantial control with very little light braking required.
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Old 02-18-2015, 02:17 PM   #28
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2009 28' International
Pacific Palisades , California
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I must apologize--I didn't answer the uphill question either! It's really a combination of what everyone says. The Sprinter 3500 has a small diesel--with the larger differential, the torque works out to be about the same as our former Suburban, but the horsepower is less. We also try to hit the bottom of the hill as fast as we consider safe for the conditions in hilly conditions, then ease off the pedal and slow (when safe and traffic is light) a bit towards the top, picking up speed naturally on the downhill. But when it's a long uphill haul, we will definitely have to drop gears at least to third. On seriously steep (anything over 7%) grades, we will be in 2nd and watching our rpm's and temp gauge like a hawk. So far, we have not had to pull off the road to cool off, but I can see one 100+ degree day in the future pulling a long uphill when we might.

Interestingly, we tend to get our best towing mileage on unpopulated highways in hilly country where it's safe to minimize brake and engine loads by allowing gravity to accelerate us in the "troughs" of the hills and slow us down as we approach the "crests." We are able to average 50-55 in this manner and get 15 mpg's on a vehicle that, not-towing, averages 19-21 on the interstate at 65-70.

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