2000 Civic LX Gas Mileage (AC on vs. AC off)

I went on a 400 mile trip today.

First 204 miles I used approx 5.5 gallons = 37 mpg
next 196 miles, 4.0 gallons = 49 mpg

This only difference between these two trips is that I used my AC for the
first 200 miles.

I had no idea the AC affected the gas mileage so dramatically.

 

This makes sense, if you look at the power levels required at steady speed
(which is what these numbers would indicate).

At a steady speed, especially one below 50-60 mph where wind resistance is
much lower, much less power is required to keep the car moving than to
accelerate or climb grades. The power consumption of the a/c compressor
remains fairly constant. As the ratio of power between locomotion and
compressor drops--as the compressor takes a bigger proportion of the
engine's output--the relative effect of shutting of the A/C becomes larger.

 

: I went on a 400 mile trip today.
:
: First 204 miles I used approx 5.5 gallons = 37 mpg
: next 196 miles, 4.0 gallons = 49 mpg
:
: This only difference between these two trips is that I used my AC for the
: first 200 miles.
:
: I had no idea the AC affected the gas mileage so dramatically.
:
I wouldn't draw conclusions based on such limited evidence. Even small
inaccuracies in fuel measurement would introduce large margins of error when
you're talking about only 4 to 5.5 gallons of gas.

In more than 65,000 miles of driving my '00 Accord, I have seen little
difference in gas mileage whether or not I was using A/C. The difference
might be more marked in the Civic, with a smaller engine, but it's unlikely
you'll see a disparity of almost a third over the long run.

IMO.

Paul