The air conditioner in my Honda Accord uses 1.2 HP according to my Scangauge. Idle is ~6.8 HP with it off, and ~8.0 HP with it on. It takes roughly 25 HP to cruise at 60 MPH on level ground, which means the air conditioner increases the engine load by roughly 5%. Personally I'm willing to live with that if it means I get to be comfortable.
Originally posted by: Connoisseur
Yeah i believe hypermiling involves several, more "extreme", methods to make your car sip fuel. Some examples:
1) Shifting to neutral during downhills to minimize rpms
2) Tailgating trucks to get the drafting effect (although this is a bit extreme)
3) Turning the engine off at long stop lights
4) Accelerating slowly
Those suggestions are all counterproductive.
1. Shifting to neutral forces the engine to use gas to idle. Leaving the car in gear while coasting engages complete fuel cutoff until the engine RPM reaches idle speed again, which means you use zero fuel instead of idle fuel. It's the difference between ~80 MPG while coasting and infinity MPG while coasting. I've verified this with my Scangauge, and anyone can learn to discern the fuel cutoff and cutin with enough practice and sensitivity to their car. LEAVE THE CAR IN GEAR.
2. Yes, drafting can increase mileage a bit, but I've found that because you can't see the road ahead and the truck likely has zero interest in hypermiling, they will hit the brakes in situations where they should have coasted, or in reaction to things you couldn't see. The result is you end up hitting your brakes, too, instead of just coasting like you would have if you could have seen the road. So it's a wash, and it's not really safe anyway. Don't put yourself in situations where other drivers make your choices for you, because they don't care about mileage.
3. Turning off the engine at stoplights just isn't safe (unless you have a hybrid in auto-start mode).
4. Engines achieve maximum efficiency at full throttle. Cars achieve maximum efficiency in the highest gear at the lowest RPM without lugging. So as any hypermiler will tell you, you get the best overall mileage by gunning the trhottle off the line and short-shifting into the higher gears as soon as possible. The idea is to maximize the distance you travel in the top applicable gear for the speed limit. So accelerating like a Grandma will actually return worse mileage. And the suggestions I've seen to let auto-transmission cars "creep" a bit before hitting the gas doesn't hold up well with the data I've seen on my Scangauge. When you creep, you slowly ramp to maybe ~3 MPG. If you hit the gas, it will be showing ~6MPG right off the bat. Again, you need to minimize the time you're not in high gear, and creeping wastes time and distance. The only exception is if you stop a bit back from the car in front and anticipate the green light a bit, in which case you're getting a little movement out of what otherwise would have been a 0 MPG idle.