I did a little spearminting (that is a Ricky Ricardo word
) on a recent trip to the factory in Lake City, Tennessee. I filled up in Staunton, VA. and drove to close to Knoxville on I-81……big time hill country through south west Virginia and east Tennessee. On this leg, I left my cruise control on most of the time, and OD off probably 75% of the time. When I thought the transmission would shift out of OD, then I would manually turn it off until it looked like I might get a reprieve. I used 89 octane, as I had read somewhere that more octane will give you better gas mileage. I drove right at 65 mpg most of the time, and little bit more than that in Tennessee when the speed limit was 70. I got 14.4 mpg…..I was not happy with that, as I have gotten 15.3 on similar interstate driving.
The next leg was from there to Lake City and back to Rural Retreat, VA. for my next fill up. I had 87 octane in my tank this time. Same speed, but instead of keeping my cruise control on and maintaining the speed on the hills, I manually worked the throttle, and lost a mile or 2 per hour on the bigger hills……just enough so the OD would stay locked in. I probably used cruise control 35% of the time, and kept the tranny in OD 75%. My mpg that tank was 16.3 mpg…..which I was pleased with.
That said, there were some other variables on the 2nd tank. I probably lost a little mileage due to getting set up and leveling in a campground. I also probably lost some mileage through several stop and go work areas/bottle necks on I-81 on this leg of the trip. I might have gained a little mileage because I had ~50 miles on the truck without the Trailmanor…….but I was driving in some stop and go traffic, and also some very curvy mountain roads around Lake City, and I doubt that my truck would get much better than that 16.3 mpg bobtailing in those conditions, anyway.
I am still driving on the 3rd tank of gas, so I can't figure that 1 in.
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