Lexus IS Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
10,731 Posts
Discussion Starter #1
Just a small data collection and analysis experiment that I used to determine if AC usage improved or reduced fuel economy. I acquired this data over a period of about 2 months.
- 90k service prior to
- RMM intake
- Window usage varied when AC was not used. (Creates drag which
reduces fuel economy)
- About 60% Highway driving.
- Gas: 76 / Chevron (highest grade 9?Octane)
- Weather: Low Humidity Avg. 65 Degrees
- Tire: Standard PSI

([email protected] level)
AC On

Chevron:[105@1/4 ] [200@1/2] [290@3/4 ] [360@f.l.o]

76:[130@1/4 ] [220@1/2 ] [310@3/4 ] [380@f.l.o]

AC Off

Chevron: [91 @1/4 ] [175@1/2 ] [255@3/4 ] [360@f.l.o]

76: [100@1/4 ] [180@1/2 ] [260@3/4 ] [360@f.l.o]

- Brandon
 

·
Registered
Joined
·
4,615 Posts
Surprising, I saw a Myth Busters episode that said that A/C gives worse gas mileage, however they have been wrong a couple of times on their shows and every car is different. And how the hell did you get THAT much better mileage at a different station?
 

·
Garage Pit Crew Chief
Joined
·
5,631 Posts
mythbusters used a ford explorer (YUCK) which is a boxbody, and the effects of air drag are much worse in the IS.

besides that test was ridiculous, since the conditions were so controlled on a closed oval racetrack with no cross/head/tail winds, just the shear effect from the SUV driving around, which does not come close to real wind with air drag from cars ahead, etc. etc.

I have started noticing that the A/C on and windows up helps if you are above 60 mph. below that, it doesnt really matter. Like the newb said,. its hwy driving mostly when u can tell these things.
 

·
Premium Member
Joined
·
27,116 Posts
I think the "official" verdict on the air conditioning/mileage issue is...

When driving at slow speeds... the A/C adds extra load to the engine and in stop and go situations this causes the engine to work harder causing more gas to be burned. In this situation it's better to drive with the windows open.

However... as you reach highway speeds... aerodynamics come into effect... and the drag produced by open windows affects the car's performance greatly. Thus in this situation the drag actually causes a bigger penalty than the a/c compressor running... and it's better to drive with the A/C on.
 

·
Registered
Joined
·
15,585 Posts
Crester said:
I think the "official" verdict on the air conditioning/mileage issue is...

When driving at slow speeds... the A/C adds extra load to the engine and in stop and go situations this causes the engine to work harder causing more gas to be burned. In this situation it's better to drive with the windows open.

However... as you reach highway speeds... aerodynamics come into effect... and the drag produced by open windows affects the car's performance greatly. Thus in this situation the drag actually causes a bigger penalty than the a/c compressor running... and it's better to drive with the A/C on.
yup, and Mythbusters drove pretty slowly with those giant SUV's on a high banked racetrack.
 

·
Garage Pit Crew Chief
Joined
·
5,631 Posts
45 mph i think. not enough to create any kind of aero drag. try that shit at 90 mph on the flats . I'm sure the one with windows down dies out at almost the same time as, if not sooner than the one with the A/C on.
 

·
Registered
Joined
·
3 Posts
You will get better gas mileage at say 60 mph with the AC on windows closed than you will with AC off and windows open. But at low speeds it won't matter much, only highway speeds
 

·
Registered
Joined
·
113 Posts
Who cares? I live in Texas and the A/C is staying ON whenever it's 80+F out. :D :D
 

·
Registered
Joined
·
186 Posts
I get about 330 miles per tank with A/C on, and 360 miles with it OFF. But that's just me.
 
1 - 10 of 10 Posts
Top