What difference does your air conditioning make on your mileage?

I've been getting 26 & 33 mpg with my ES350 but have had the AC on pretty much full time since buying the car in June.

Now that the weather in NC has cooled a bit I've found that my mileage has improved about 1.5 mpg without using the AC. That's a 5% penalty for using air.

I prefer driving with the sunroof open and cool air coming in versus being buttoned up with the AC on - if the weather allows it. 5% better gas mileage makes it just that much sweeter.

 

Don't forget that if you cool the car by opening sunroof, windows, etc., the additional drag from the poorer aerodynamics will probably be at a penalty a lot greater than 5%.

Assuming that the compressor cycles on and off as demands change, a better bet for maximum mileage would be to just leave the system on Auto - then as the weather cools, the a/c would just run less and less.

 

My 5% improvement is with my windows/sunroof open and the AC off.

The best mileage would be with no AC and all the glass closed.

 

dreyfus,

I have seen posts you have done on here and I have to say you seem a very patient and resourceful person to have saved yourself aggravation and money with DIY means of addressing Nav., other on here.

I say spoil yourself with the AC even if it ends up costing 5% fuel to use it, your patience and cost saving measures of your DIY approach more than offset and justify you spoiling yourself here and there.

 

BTW: I have not done this but it makes sense at some point to try to over time, say a year, save quite a bit on gas.

The octane requirement for our car is 91.

A guy I know fills his tank 1/4 full first with 89 octane and then adds the balance of 3/4 tank with 93 octane and he is netting in excess of the required 91 octane doing this and insists no difference between doing this and repeatedly filling in the past with exclusively 93 octane.

If it was a 50/50 mix it would yield a blend of 91 octane, since it is 1/4 to 3/4 he says it is over the 91.

According to him you should do this when needing to fill the car nearing empty with the 89 first and then adding in the 93 which mixes it all together.

A more brave(?) person could actually do the 50/50 it seems and save even more on gas over a period of time.

 

Thanks, ES350Bob, I do use the air whenever the weather is too hot or humid, which is pretty much half the year here in NC.

I was just interested in seeing from other owners what their fuel saving have been without AC.

As far as fuel goes, I'm using straight 87 octane now. I've experienced no difference in engine performance, engine sound, or mpg between 87 octane and 93 octane. If there were the least pinging or any other consideration then I'd use the higher octane, but to date (4,600 miles) there has been no difference. BTW, I drove the first 2,000 miles using 93 octane only.

But this is off topic. Has anyone else documented their mileage improvement without air?

 

I haven't documented my fuel mileage difference, I know there is a little. The fuel gauge doesn't seem to drop as fast.

When I drive less than 50 MPH, on average, I have the front windows down in ninety degrees or less. Down the interstate, windows closed and A/C or vent on, depending on the outside heat.

The point may be to insure you cycle run the air conditioning system for five minutes at least once a week, every season through the year. This keeps the A/C functional when needed and reduces freon weeping from the system. Additionally, keeping the seals soft and moving the valves and duct control vacuum "motors".

 

Too bad the above wouldn't work in states such as CA where the highest octane gas widely offered is 91...

 

I believe that if you leave the climate control on automatic that the AC is on all the time. In cooler weather it mixes in the heater to control temperature. You may notice in cold weather up north that the windows stay defogged in the auto mode.

 

no. Even though A/C is illuminated, it doesn't mean it's always on. It will come on and off depending on the situation, hence automatic climate control.

 

The Avg. displayed for me at start of car is 19.6 mpg. I don't travel highway where speed is like 55mph plus, but typically residential half mile to road where limit is 40mph and I use the AC.

This low mileage may be that my car makes that knocking tapping noise diagnosed as a valve problem.

Not sure how needing shims added to valves to make them right affects the gas mileage or to what degree.

 

FYI, on the track, it can eat up a good min. of 10 hp, and up to .2 or so in lost time in the 1/4 mile.