I'm driving across the country from San Diego to Bath Maine.. for most of my trip I've been taking I70.. well my strangest observance is at an average of 85 mph for 200 miles(through most of Kansas)(yes folks that's 85 mph average, with no tickets thanks to a CB I bought and using to monitor truckers reports for Smokey)I averaged 30.9 mpg.. The next 200 miles that I measured I averaged about 73 mph(going through Missouri) I only got about 27.1 mpg.. the terrain is about the same, flat as a billard table, so that dosn't have much to do with it..

I'm guessing that we just get better fuel economy at higher speeds, because of less pumping loss from our engines at higher speeds?????

 

well... average speed doesn't tell the whole story. Did you driving style change? Did you accelerate harder or more often(ie slowed down and then sped up)?

Those could all effect it.

 

a light incline is very unnoticeable, but may have been the reason for the decline in your average.

By the way, how long did the cross country trip take you, and with how many stops, how many hours of consecutive driving?

 

Different pumps could top off at different levels. Or the gauges could be off. If you could do that consistently regardless of where you fillup, then some is definitely wrong. At higher speeds, there should be much higher aero drag. It's physically impossible for a car, that doesn't change its shape, to be more fuel efficient at higher speeds than lower speeds.

 

well.. I'm about 40 miles north of Chicago now, stopped for a couple days at a friends house, and I'll finish my trip around the 28th or 30th... I'm filling it to the stop on the pump, then let it click one more time..

speed changes were more agressive with the higher speed (messing with a couple college girls in their SUV for about 45 minutes) then about 15 minutes into the tripple didgits, with the cruise control set at 105.. the 73 average speed was done with cruise control on, with very few places that I had to slow down..

I'll do a full iteneary for my journey when I get to Maine, giving total fuel spent, with average fuel economy..

 

A headwind vs. tailwind could also make a significant factor in aero drag. Also, the traffic density and drafting effects of being behind another car significant impacts the airflow around the car. Have you ever been driving with the top down and noticed the difference in wind buffeting whether you're in 'clean air' or following somebody at 10 carlenghts? All of these things would make a difference in mileage. Also, I've found top down to be about 4mpg worse than top up driving at highway speeds.

Still, automatic shutoff at the pump is probably the likely culprit.

 

I don't think the 30.9 mpg at 85 is a true number. I feel sure that do to pump shutoff or being on a slant caused the the tank to not be completely full. Unless you got that over several tankfuls there is a measurement error somewhere. I cruise at about 80 and conmsistently get 27-28, less if A/C is on.

 

gas differences between states? here in california, we pay more for gas that gets us less ... but is much cleaner burning. maybe your second state has is a cleaner blend than the first.

epi

 

Going east through Kansas on I70 seems to yield higher MPG. I think you drop about 1500feet (a guess) from W to E, and there is usually a west wind (and can be strong too). I once averaged an honest 20MPG going E through Kansas in an old Tahoe with 350 V8 at 85 MPH.

 

Wow! A 3000 trip!!! Ahhh, how's yur back?