This is not a question about how to save gas.. the quetions is for a mechanic or pro…every car reaches it opt mpg a diff speed i drive a 2007 honda civic 1.8L with 5 speed manual with stock trans and gears.
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What Used cars have best mileage?

You should see about 48-50 Mpg HWY and 32-35 City
Nothing less than 44 Hwy Thats if you are travelling around 60 MPH or so… once you cross over to 75 MPH then expect around 40-42,
i would say between 35-37 highway
–good luck
Okay, I am not a mechanic but I am an owner of a 2006 Honda Civic w/ an automatic. I drive my car 90 miles a day and average around 38 mpg. I obtain it by keeping my speed between 70 mph and 73 mph. I recently drove to Tennessee from New Orleans and averaged 43 mpg on the trip there and 45 mpg on the trip back. I set the cruise on 70.
City 30 & Hwy 38
down hill with the wind and the car in neutral
and the engine off
you will get great MPG
You can usually tell your optimal mileage speed by the feel of the car. I can’t say that I know what the speed will be for each gear, you’ll have to figure that out on your own or wait for someone who knows. I can say that the engine will be most responsive in the area of best mpg. This is because the air and fuel is being mixed the best. In my 93 automatic on the highway, when my car is in D4 (overdrive) it’s somewhere around 70mph. It will be at a point where you can almost coast, and with the slightest press of the pedal you will accelerate without much drag. Typically a lower rpm per higher speed will result in better mileage, but not always true, cause you don’t want to be causing too much labor for the engine (say you are in 4th gear at 25 mph…your rpm will be low, but you are trying to dump a lot of fuel to keep it going steady or faster)