What year is your 4.8 ? Do you have the 6 speed auto? That's great milage! I do run faster then you, normally a couple miles over. In ND that means 77-78 mph. That's when I only get in the 16s. I like to get wherever I'm going ASAP. OMV will now tell me to slow down and save money. LOL
There was a time when I was like that. 2-3 MPH over the limit, because you can get away with that without getting a ticket, right? Plus, 72 in a 70 versus 62 in a 70 gets you an extra 10 minutes every hour, and those add up. An 8 hour run nets you every bit of 80 minutes to get there early or for an extra hour of sleep somewhere.
Then, I had a problem with the Sprinter with a combination of high pressure injector pump and fuel rail which caused a modified "limp home" mode where I had plenty of power at all speeds, except I was maxed out at about 63 MPH. It was like I had a governor on the engine. I ran that way for about 4 months. The first week was excruciating because I felt like it was taking
for-ever to get anywhere. After another week it suddenly wasn't so bad and I wasn't any longer in any hurry to get back home for a $2000 repair. So I just ran that way for a while. Instead of looking for a load to get me near home, I instead just waited for a load that just so happened to take me near home. Turned out it was 4 months. I discovered I really wasn't losing any time, and I was more relaxed after the runs.
But the big one was the added 3 MPG I was getting over time. 22 MPG versus 19 MPG. At $3.50 a gallon it's the difference between 15.9 cents a mile and 18.4 cents a mile, 2.5 cents a mile. It's not much, but also at the time the reduced speed meant less wear on tires, bearings, brakes, and cooler transmission and rear end oil temperatures which translates to reduced wear on those parts, as well. The math works out to at least an additional half a cent a mile for reduced wear, so it was about 3 cents per mile overall.
In those 4 months I logged 33,000 miles. At 3 cents per, that's $990 in real money. Free money. And it paid for half the injector pump and fuel rail repair. An extra 2-3 cents per mile for most vanners will mean an extra two grand a year that you don't have to spend on fuel. That's serious money.
I've long since had the van repaired but I continue to run not 2-3 over, but generally 3-5 under the speed limit. And it's rare that I will exceed 65 regardless of the posted speed limit, even out west where it's 75 and 80. Not only do you get better fuel mileage going a little slower, but there are many situations where increased fuel economy becomes magnified thanks to a phenomenon called "long distance drafting". It's most readily observable on the Ohio Turnpike, and other places where it's relatively flat with a fair amount of traffic, where you travel 3-5 MPH slower than most of the other traffic on the road, and as they whiz by you their drafting wake literally pulls you along behind them. I've gotten just stoopid mileage on the Pike and a few other places, like 26 and 28 MPG. It's not always that good, of course, but whatever it is, it's always better to have them drag you along, than it is for you to do all that extra work in dragging them along.
There are two undeniable truths of traveling along the highways like we do. One is, if you are getting passed on the right, you're in the wrong lane. The other is, if you are passing more people than are passing you, you're driving too fast.
