I've always been of the mind that cruise control would get me better gas mileage on my 3 hour trips to Cleveland. Today I tested out to see what the difference was, on the way there with cruise I got 33.4 MPG. On the way back I got 37.6 MPG. That is an amazing difference. This is on an Auto Cruze. I'm going to up my tire pressure and see what I get on the same trip on Thursday. Thanks for the great write-up!
With the cruise control in the cruze & the automatic, try using manual shifting mode. Instead of downshifting once you loose 2MPH like in full automatic mode on a hill, it will allow you to loose 8+ MPH(never fully tested to see if the cruise will eventually kick off). before I ever loose to much speed or slow other traffic I will manually downshift.
In my area with lots of rolling 150-300ft hills with steep grades allowing the car to loose more speed before downshifting, that means I can make it over half way up the hill(or all the way)with no downshift at all. Again these are steep grades that would normally kick down on every hill near the bottom, in a 30 mile drive that would be at least a dozen unneeded downshifts.
The Cruze control will kick off at -15 MPH from the set point. This, and the ability to set as low as 25 MPH, seems to be a standard on GM vehicles. Most people will get better mpg using Cruze control on the highway, but if you pay attention to what's coming up you can beat the mpg from the cruze control system.
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I make the same trip multiple times a week and looking at the weather I was going into a slight wind this time, I've been hovering around 33-34 MPG until this trip, I had about half a tank left at 32.8 MPG (80-20 HW/CT split) on the way up and when I got there not using cruise control I was up to ~35MPG. I'll see what I get when I make the trip on Thursday. I do believe there is a slight elevation increase between Columbus and Cleveland but I haven't looked into it. Edit: Hmm its the opposite of what I expected, its an elevation increase to Cle from Col (about 250ft higher in Col). I thought it was the opposite for some reason. Maybe I did jump to conclusions though as so far on this tank it was 99% highway. Ill wait till Friday to see what happens.
I can beat the cruise control up to about 62 mph. After 62 mph the MPG's on these cars really slides downhill, cruise control or not.
If going up a very slight incline at 35 mph, shifting into 5th has better fuel economy than being in 6th. Conversely, going on a slight downhill at 35 mph, 6th is the gear to be in since the engine is essentially idling at 1100 RPM at that speed.