put her in neutral on downhills and get behind a large truck on uphills.

 

Matt - Two things - 1. How fast were you driving? 2. Did you actually put 16.2 gal into the tank or are you going by the capacity in the owner's manual?

On my old 99 2wd, I usually got about 18 or so on the highway with a moderate load and OEM size tires. Best I ever got was 19.5MPG. That was driving about 75-80 with the cruise set. Driving 80 compared to 72-75 will cost you 1MPG. Setting the cruise with any hills will cost you some, because the computer is more agressive than your foot would be when maintaining speed going up grades. You're also losing 0.5 MPG or so because of the roof rack - that's why mine's off until gas prices get below a buck-fifty again. You also need to consider the fact that you have larger than OEM tires, making your ODO off by about 3.2%, or about 0.6MPG.

If you indeed drove 270 mile on a MEASURED 16.2 gallons, then you got 16.7 MPG + 0.6 MPG tire correction gives you about 17.3 MPG. Then add 1 MPG for speed correction and 0.5 MPG for the roof rack and you'd be at about 18.8, and that's if and ONLY IF you actually put 16.2 gallons in the tank...

 

i get 16 mpg , 300 miles to the tank on 33's. i also like to draft behind trucks and go no faster than 65mph.


try changing your plugs , pcv valve , fuel filter , clean you injectors , etc ......

 

Do yourself a favor and back down to midgrade since all your doing is throwing money down your tank. Higher octane is only needed if your vehicle pings on lower octane like an SC'd runner would do.

 

Octane - it is not more efficient to use premium if the engine doesn't need it, you might actually get worse mileage and you might do more long term harm than good.
Yes, your tires are hurting your efficiency a little bit.
Tire size throws off calcs, don't forget to correct the mileage reading for the tires.
Use the odometer reading (corrected if needed) and the gas receipt to compute the miles per gallon.
Drag increases exponentially (inverse square law) - above a certain speed the drag increases so much that mileage will REALLY suffer, 80mph is far above that speed for something with the aerodynamics of a brick. The magic speed is around 60 by the way, and drag goes up really fast above that speed.
Yes, a roof rack will generally take 2-3 mpg off your mpg. Larger frontal area is worse than poor aerodynamic shape.
One Tankful is not an accurate sampling. Keep records and review after about 3 tanks.

And lastly - Use the gas guage to keep from running out of gas...

 

I just checked my mileage this AM! 16.45 (uncorrected)MPG 90% interstate driving at 85 MPH. OH WELL, I guess if I wanted fuel economy I would have bought an Echo...

 

If you dropped that to 70-75MPH, you'd get over 18...

 

Out of curiosity, What kind of mileage do you get Andy?

 

doing 75 or so w/ 285's and a S/C - about 16.5-17 on the highway and a dead-on 16 around town. I'm currently in need of a front O2 sensor though. I don't have a CEL yet, but I know it's running a little rich because I have the tell-tale black soot all over the exhaust and poor gas mileage. After I change it, I imagine it will jump up at least 2 if not 3 MPG's.

 

It's good to run 92/93 octane every once in a while because it runs hotter and can help remove some build up. But no sense in running it all the time as long as your running decent gas (chevron, shell, etc)

I get a pretty steady 17 uncorrected, I have 265-75-16 REVO's. About 265 miles per tank (Ive got a 15.5 gallon tank), in traffic or on the freeway. I usually cruise around 75-80. On long trips I try to stay under 75 and I'll get closer to 18.