Fuel Economy 101

[Photog]

Since I asked for this section, I figured I should toss in the first thread.

Mark (Markopolo) has a thread in the "RV Education 101 Articles" section, specifically about fuel economy.

Here is a link to that thread. http://www.classbforum.com/phpBB2/vi...php?f=27&t=206

Our recent experience with our lifted (4") Roadtrek 190V, was an average of about 15 mpg. We drove 2500 miles, from Gig Harbor, WA, to southern Utah, and back. Most of the distance was driven on Interstate highways. We could have improved this by driving a little slower, but the lanes on the Interstate that were smooth, were full of folks driving faster than 60 mph. So we stepped up our speed to 70 mph, with a nice, smooth ride, and lower fuel economy.

I installed a Scan Gage II, to monitor our 6.0 Vortec Chevy engine. With this, I can see how much difference a little "foot action" has on the fuel economy. Here are a few things we have learned:

1) A little extra speed down hills, to carry the momentum up the next rise, is a big help.
2) Cruise control is good on flat ground, but good foot control is better everywhere else.
3) Don't down-shift, if you don't have to. Downshift to protect the engine and tranny from overheating; but don't do it otherwise.
4) Smooth, strong acceleration, up to highway speed, is better than either wide open throttle (WOT) or slow acceleration. Slow acceleration provides poor MPG (4mpg) for an extended period of time, where strong acceleration has poor MPG (3mpg) for a short period of time.
5) When using the Scan Gage II, I try to keep the MPG reading from going below 12mpg, in the hills. This is not always possible, but if I try to keep it above 12mpg, as much as possible, I get better mileage overall. It is easy to press the throttle a little more, gain nothing, and only get 9mpg.

[Johnny R]

Originally Posted by Photog

3) Don't down-shift, if you don't have to. Downshift to protect the engine and tranny from overheating; but don't do it otherwise.

I like downshifting in my car as well as the camper, especially downhill when the vehicle wants to exceed the speed limit. Perhaps the longer brake pads/rotors life will offset the fuel usage? Not sure the difference is measurable, and I have other things to do too.
PS:Markopolo beat you to it, I think, with the fuel thread?

[Photog]

I see what you are saying.

I was not very clear. I was speaking of downshifting to climb hills on the highway. These engines seem to be able to run a 90% load, for short times. If it is a short hill, and you can avoid downshifting, the gas mileage will be higher. The higher revs of a lower gear, will drink more fuel, even though you don't need as much throttle.

Again; downshift if necessary to protect the engine/tranny from overheating. If you are towing anything, downshifting to climb hills becomes a standard routine.

Since this is a minor point, you may want to ignore this "no downshift" suggestion.

[Photog]

Originally Posted by Johnny R

.........PS:Markopolo beat you to it, I think, with the fuel thread?

I think he posted one in, while I was composing that 1st post. There is 6 minutes between them. The section was empty when I started writing.

[Mike]

Originally Posted by Photog

I see what you are saying.

I was not very clear. I was speaking of downshifting to climb hills on the highway. These engines seem to be able to run a 90% load, for short times. If it is a short hill, and you can avoid downshifting, the gas mileage will be higher. The higher revs of a lower gear, will drink more fuel, even though you don't need as much throttle.

Again; downshift if necessary to protect the engine/tranny from overheating. If you are towing anything, downshifting to climb hills becomes a standard routine.

Since this is a minor point, you may want to ignore this "no downshift" suggestion.

I have the 5.7L and I try to let the automatic transmission decide when to shift. It usually downshifts
uphill when the van is losing speed under climb load, but it's a disaster on a long uphill in hot weather.
Once in Cape Breton and again in Lake Placid we tried hills in the heat of the summer. The first we
made, the second we didn't, and had to turn back. I can't do much about it, short of installing a bigger
engine, because I'm quite sure my van is under powered for it's weight. Mileage is the farthest thing
from my mind. On go the four ways, keep right, hope for the best.

[Photog]

Originally Posted by Mike

I have the 5.7L and I try to let the automatic transmission decide when to shift. It usually downshifts
uphill when the van is losing speed under climb load, but it's a disaster on a long uphill in hot weather.
Once in Cape Breton and again in Lake Placid we tried hills in the heat of the summer. The first we
made, the second we didn't, and had to turn back. I can't do much about it, short of installing a bigger
engine, because I'm quite sure my van is under powered for it's weight. Mileage is the farthest thing
from my mind. On go the four ways, keep right, hope for the best.

I have found a few long hills that I needed to drop down a gear, and keep the RPMs up in a good torque range, and keep an eye on the water temps. As long as the torque converter stays locked, the tranny temps should stay low.

For fuel economy, I let the tranny do the downshifting also, but I slowly let off the throttle, as the climb continues, to keep the load low enough to prevent downshifting. This keeps the MPGs up, as the van slows down. This only works when I am not holding up traffic, and the hill is not to long.

If the hills are long, like they can be climbing through the Rockies, Sierras and Cascades, fuel economy takes a back seat to engine and transmission protection. You are right, these rigs are heavy. A diesel engine would make more sense.

[Mike]

Originally Posted by Photog

I have found a few long hills that I needed to drop down a gear, and keep the RPMs up in a good torque range, and keep an I on the water temps. As long as the torque converter stays locked, the tranny temps should stay low.

For fuel economy, I let the tranny do the downshifting also, but I slowly let off the throttle, as the climb continues, to keep the load low enough to prevent downshifting. This keeps the MPGs up, as the van slows down. This only works when I am not holding up traffic, and the hill is not to long.

If the hills are long, like they can be climbing through the Rockies, Sierras and Cascades, fuel economy takes a back seat to engine and transmission protection. You are right, these rigs are heavy. A diesel engine would make more sense.

I have to let up on the throttle, almost regularly on any uphill grade greater than or equal to 6% I've found.
And that's when it gets scary on an uphill where you're in heavy traffic, and the only vehicles struggling more
than you, are loaded semi trucks, and sometimes they're even passing us. The climbs through CO and UT and
even AZ in parts, along I-70 and I-40 can be difficult for us, but luckily we're rarely in a hurry to get anywhere.
We've had some challenging climbs in the Gaspe and Cape Breton, as well as the Adirondacks.