So I'm thinkin I may have to try an highway drive at 75 MPH and measure my milage, and then again at my normal 85 and measure again. Great info, Phineas!

 

Yeah, we need someone to do a long-distance trip on cruise control at 80 and 85 mph. Any takers?

 

75 mph will not keep you in the higher mileage band. 71 mph indicated is where you need to be in 6th to keep the secondary injectors from opening. 72 mph is no man's land and actually gives crappier mileage (<18mpg in 6th on cruise for 50 mile flat, straight no wind run) 72 seems to be fast enough to open the secondaries and yet still slow enough to be absolutely no fun at all. I make the same 50 mile run 2 x per week and have tried 69, 70, 71, 72, 73, and 80+mph. Not enough difference between 72 and 80 to bother or care to do it again. If your primary goal is mpg, keep it under 71 in 6th.

 

PhineasFellOff, did you mention what gear you were driving in, or did I simply miss that part?
(I mean what gear you were cruising in)

 

Sorry, I just assumed that everyone would assume I was in 6th gear. I actually did everything- 60, 65, 70, and 75 mph- in 6th gear.

 

The MPG posted for the LA to Jax and back trip matches pretty closely to what I have experienced on my long trips, but I don't think I have the patience to test it at 60 MPH. My norm on Interstate highways, average traffic is 75-80 MPH and I consistently get 21-22 MPG at that speed. Yesterday I was in a hurry driving back from Orlando with the AC full blast and went non-stop from east side of Orlando to Tallahassee (on one tank, no rest stops) running 85-90 MPH nearly the whole way. I was surprised to find my MPG did not drop appreciably - got 21.1 MPG. This included a few hard accelerations when I had to get past some traffic that wanted to block all three lanes on I-75.

BTW, the total miles 265, using mid-grade (91 octane?) BP gas, MT. My in-town mileage averages 15-18 MPG, usually very short trips, stop and go traffic, mostly conservative driving winding it out once in a while.

 

Hmm, my highway results match yours but my commute is generally no better than 14.2 unless I have a longer trip mixed in. Maybe I should start shifting before the bell goes off. (Actually, I most often shift around 6K, as it produces an acceptable torque zone for the next gear, but also dooms me to having the injectors open much of the time.)

 

From what I've gathering from all the fuel consumptions post here, it seems that maintaining a constant speed is the key to getting a decent MPG.