Gas Mileage

[Bill]

Mtnguy Chap posted

From now on in similar conditions, I think I am going to use the cruise control less, and try to keep it in OD more.

Chap, I've had the same experience. The problem is that the cruise control is incredibly "brittle" (my word for it) - it has no flexibility. If you set it for 65 mph, and you start up a hill, and the speed starts to drop just a smidge, the cruise control will mash the accelerator in an attempt to maintain 65 mph come hell or high water. The result is that the transmission downshifts, maybe even twice, the engine RPM climbs, and gas mileage plummets. And to add insult to injury, when you start down the other side of the hill, the cruise control will entirely release the accelerator, resulting in engine braking, as it attempts not to exceed 65 mph. Why would I want to brake as I descend a moderate hill?

So I use cruise control only on the flattest of flat land, where these things won't happen. If there is any sign that the cruise control is getting carried away, I turn it off and modulate the throttle with my foot. It has a noticeable effect on gas mileage.

Bill

[wbmiller3]

On our trip last month over the Texas plains I got 14+. This was highway cruisin', no faster than 65. The only other tank I calculated on was 13+, same conditions but more mountains.

I bet either of these is better than what I get driving to work on city streets sans TM. But, I hardly ever freeway cruise for a whole tank at 65, without the TM, so can't compare apples to apples.

Originally Posted by Bill

The problem is that the cruise control is incredibly "brittle" (my word for it) - it has no flexibility. If you set it for 65 mph, and you start up a hill, and the speed starts to drop just a smidge, the cruise control will mash the accelerator in an attempt to maintain 65 mph come hell or high water. The result is that the transmission downshifts, maybe even twice, the engine RPM climbs, and gas mileage plummets. And to add insult to injury, when you start down the other side of the hill, the cruise control will entirely release the accelerator, resulting in engine braking, as it attempts not to exceed 65 mph. Why would I want to brake as I descend a moderate hill?

So I use cruise control only on the flattest of flat land, where these things won't happen. If there is any sign that the cruise control is getting carried away, I turn it off and modulate the throttle with my foot. It has a noticeable effect on gas mileage.

Bill

That was what I suspected before my experiment, and confirmed with the mileage results. You can get a much better feel of what your tranny is getting ready to do with your foot on the accelerator.......even with the electric "linkages" that the manufacturres use today vs. the old mechanical ones.....you got really good feed back with those.

Chap

I just finished a 850 mile trip pulling a 2619 fully loaded including the 40 gal water tank. My 2008 Ridgeline averaged 16.2mpg. I had the cruise control set at 57mph. The speed limit towing in California is 55mph and the CHP enforce it. The AC was on all the time. The Ridgeline motor is probably not fully broke in as it only has 4,400 miles on it. I was pleased with the mileage. Now if gas prices would come down I would really be happy.

[Wavery]

We drove our Chevy S-10 P/U (4.3 V6) 1100 miles (each way) to pick up our TM 2720. No mountain driving involved.

We drove about 75-80 MPH on the way to pick it up. We got 24MPG. On the way home we drove 60 MPH and got 16MPG.

About 2 sago we drove 600 miles in the same P/U at 60MPH (no tow). We got 27MPG.

Originally Posted by TREXHUNTERS

What gas mileage do you get pulling your TM versus not pulling?

... I normally get 18mpg highway under 3K ft. For some reason I get 1-2 mpg higher at higher elevations.

The mpg increase at higher altitudes is likely due to decreased drag -- the air is thinner at high altitudes. On two different trips (no TM) to the east coast I'd see about 19 mpg at 65-70 mph in Colorado, around 18 or a touch over in the higher parts of Kansas or Nebraska, and down to 17-17.5 at lower elevations (under 2.5-3K feet). I'd lose about 1-1.5 mpg additional going through the mountains of Maryland and West Virginia on the Interstate at 65mph.

Generally I'll lose 2-3 mpg towing the TM, but when a lot of the trip is on steep mountain roads I'll lose another couple of mpg. Because my Triton V8 is a flex fuel engine, I tried E85 for a few tanks, and discovered that I lost 2-3 mpg without the TM, and a bit more with the TM behind. With E85 on steep mountain roads (going to Mueller State Park above Colorado Springs, for example) I'd sometimes be down to under 10 mpg, but adding in the more level parts of the trip I typically have around 11-11.5 mpg on E85, closer to 13 if the entire trip is more level. There seems to be a slight power loss on E85, as well, since it doesn't seem to pull steep grades as well with E85 as it does with regular unleaded. Note that unleaded in Colorado usually includes 10% ethanol, so running E85 is going from 10% for regular to near 85% for E85, near 85% because the pump label says "up to" 85%.

I've noticed several comments in this thread about octane. In Colorado (and other high places) the gas companies sell 85 octane as unleaded regular and 87 octane as the mid-grade, vs. the 87 and 89 you see at lower elevations. When I bought a 1989 Ford Ranger in 1989, the manual said to use a minimum of 87 octane, so I bought the mid-grade for a long time. As gas prices went up I decided to try regular (85), and it ran fine, with no pinging and no noticeable change in mileage or performance. So from that point on I've run the 85 octane, including the 2003 Sport Trac I had and my current F150.

I traded my Chrysler minivan with a Tahoe Hybrid recently and I'm getting 17mpg towing from Jekyll Island to Woodstock, GA about 350 miles. I set the cruise control to 64 mph which gives me better economy than 65 mph. When not towing, I'm getting 24.5 mpg. The sweet spot of the Tahoe Hybrid seems to be 70mph when not towing and not the 55mph.

I'm posting my fuel economy numbers on my blog - Everything Lexis. As of now, this is the only post since the blog is new but I had friends interested in my tests so I decided to post it first. Check it out.