I don't know GM cars like I do Ford products, but my dad has a 1999 Mercury Grand Marquis with a 4.6L V8 w/od and he get about 28 mpg on the highway with it at 70-75mph using the a/c and c/c. It will get about 24 on local short trip driving. I don't think it should be any trouble at all to get 30 unless there is something bad wrong with the car. Road Warrior says the old EPA rating is 29 mpg so you only have to get less than 4% above epa if you drive 55-60 that shouldn't be a problem. How much of the trip is interstate driving and how much is stop and go?
Right now I don't know what engine it has. I'm pretty sure its a V6, but it could be larger than a 3.8. I figure if he got 24 on that trip, and 30 was a nice, round number. I now realize that if I do reach my goal I would have a 25% increase in mileage... with minor mods and careful driving. Another thing I should mention. The trip is from Sterling, Va (near Dulles airport) to Berkley Springs, WV. The drive will be mostly highway, but it will not be flat. Hills and mountains, which if I play my cards right means lots of DFCO.
I haven't made the trip to Berkley Springs in about 2 or 3 years. Suffice to say that I won't be able to anticipate the road ahead. That being said I will be driving in hilly and mountainous terrain. I'm thinking DFCO as much as I can.
I also asked him what engine it has. He has the 3.8 V6 in it.
My 95 supercharged Riviera would get 27-28 on the highway at 70-75MPH with no hypermiling techniques.
That car would coast forever, must have been a fairly low CD. I had to relearn my timing to keep from coasting too close to the car in front of me when traffic slowed down.
Jay, you can do it or get real close with the park avenue.
I just got back from Boston per my prior post above and clocked 30.2 down and 29.9 back. Had the a/c on for the trip home for half way. Going through the mountains killed it a little. It went to 29.1 through the mountains and then after I hit flatter road, it creeped back up to 29.9. Had the cruise on 70 part way and used my foot part way. Pretty much maintained 70 all the way. RPM's were 1,900 at that speed. Didn't do anything elce to help gas mileage except I am not an aggressive driver.