A/C turned off gained 30% fuel efficiency?

[motosan]

For some reason, my 1 yr old M3's A/C started to stink at temp 71-74 while outside temperature was between 65-75. So I turned off A/C for the past few weeks. And I noticed that combining with minimum use of DCT increased fuel efficiency by 30%+. Overall it also had 40-50% traffic time.

Full tank usually used to give me 180-220 miles with 40-50% DCT drive and full A/C on. But now I can get 270-300 full tank.

Has anyone experienced the same thing? It's a bit odd how A/C consumes this much gas...

If not, perhaps it was because that my dealer cleaned up the fuel injector, which my dealer claimed to be dirty enough to be cleaned, just after 1 yr of ownership...

[MysticBlue]

Originally Posted by motosan

For some reason, my 1 yr old M3's A/C started to stink at temp 71-74 while outside temperature was between 65-75. So I turned off A/C for the past few weeks. And I noticed that combining with minimum use of DCT increased fuel efficiency by 30%+. Overall it also had 40-50% traffic time.

No. C'mon, do you really think A/C would make a 30% difference in gas mileage. That's ridiculous. I don't know what you mean by "minimum use of DCT" but A/C use is very negligable on mileage. Definitely would not be anything close to 30%.

[IFX]

A/C does NOT use that much gas.

[schnell325]

Maybe 3%??

[piloto]

Why would a 1yr old car need to have its injectors cleaned? Even the crappiest gas sold is relatively clean, not to mention the fact that your fuel filter traps the majority of debris. As for carbon buildup, again, why would that happen so quickly? Something seems odd. Was the car tuned, to where it was running super rich before?

[Erie Von Otto]

Someone else on another thread mentioned the injector cleaning. There was much backlash about dealership incompetence/money shanking...

[SchnellM3]

Originally Posted by ottoblotto

Someone else on another thread mentioned the injector cleaning. There was much backlash about dealership incompetence/money shanking...

+1 Just the dealer trying to make some extra $$$

[BMRLVR]

Originally Posted by motosan

For some reason, my 1 yr old M3's A/C started to stink at temp 71-74 while outside temperature was between 65-75. So I turned off A/C for the past few weeks. And I noticed that combining with minimum use of DCT increased fuel efficiency by 30%+. Overall it also had 40-50% traffic time.

Full tank usually used to give me 180-220 miles with 40-50% DCT drive and full A/C on. But now I can get 270-300 full tank.

Has anyone experienced the same thing? It's a bit odd how A/C consumes this much gas...

If not, perhaps it was because that my dealer cleaned up the fuel injector, which my dealer claimed to be dirty enough to be cleaned, just after 1 yr of ownership...

You must be using the AC on your M3 to cool your house

[Mike van D]

Agree with the others, 30% seems a bit unreal...

[motosan]

Guys
Thanks for the replies. Yeah, the other thread about injection cleaning was also posted by me.

I ended up doing the injection cleaning because I brought in my car to fix the dang dashboard rattling. I had to leave my car at the dealership for over a week for my business trip. I wanted to make my SA feel "more obligated" to take care of my car, so I ate up whatever he had to sell me to meet his quota (of course there's always a possibility that he was not lying about getting my fuel injection cleaned).

Anyway, good news is that I got my car back and rattle is fixed (third attempt, hopefully it stays fixed). And I notice what used to be 180-230 miles full tank now can go over 270 easy with most times A/C off and minimum manual shifting and throttling. But I know it's weird how A/C can consume this much gas. That's why I posted my question.

What I'm going to do is:
1. At the next gas fill, I'll turn the A/C back on and see whether mileage is affected or not

2. If it is not, it probably is my fuel
Injection getting cleaned? But I suppose modern gas stations all have solution in the fuel to clean up. Perhaps I've got some bad gas stations around my neighborhood?

3. I'll also bring my car to a different dealership check something else about car in next few weeks after my project finishes for second opinion. And if they also say that I need throttle body cleaning that either means I unbelievably found a honest stealership?!?! Or both dealerships are shady as hell.

By the way, how much mpg are you all getting? I used to get 16 mpg and now I'm getting 19-20mpg now.

[FVM3]

I always leave the a/c on and roll up all the windows and after changing the exhaust i almost never switch on the a/c and roll down window all the time. Miles i go on each tank is almost the same. PS I always switch the ac to the lowest temp and level 3-4 fan speed.

[BMWJ]

on the highway I got better mpg with windows up and A/C on than I did with A/C off and windows open.

[CrazyIvan]

Originally Posted by BMWJ

on the highway I got better mpg with windows up and A/C on than I did with A/C off and windows open.

Less drag

[BMWJ]

^-- yup. averaged 1 mpg better

[alpina527]

I had my old 2002 e46 M3 injectors cleaned after 75k miles and noticed zero difference.

How many miles has your 2011 DCT done to warrant cleaning the injectors?

[motosan]

alpina527:
Less than 17,000 miles...

[Mjolnir]

The AC off won't increase the gas mileage that much. But you may want to try my method. I use a long straw from an empty Pixie Straw and blow bubbles in my gas tank. It aerates the gas and I noticed a 23% increase in my gas mileage. Just make sure the Pixie Straw is completely clean because you don't want sugar in your gas tank.

[docbolo]

Originally Posted by Mjolnir

The AC off won't increase the gas mileage that much. But you may want to try my method. I use a long straw from an empty Pixie Straw and blow bubbles in my gas tank. It aerates the gas and I noticed a 23% increase in my gas mileage. Just make sure the Pixie Straw is completely clean because you don't want sugar in your gas tank.

Yes and I filled my tires to 60 psi and now I get 40 mpg.

[roastbeef]

i met a dude one time that extended his fuel line and rigged it up to wrap around his radiator hose about seven times to heat up the fuel. his reason was so the fuel would heat up- expanding the atoms, and it would stretch his fuel farther.

no joke, this dude was serious.

[serranot]

Originally Posted by docbolo

Yes and I filled my tires to 60 psi and now I get 40 mpg.

Don't laugh.

I was irritated that my local service station had gotten rid of free shop air for one of those machines that cost money. Not that I give a rat's about $.75, but it can be a hassle. Anyway . . .

One day I was there and saw some old guy using the shop air. After he left I asked the manager why the old guy didn't use the new machine like everyone else. Turns out he likes to put 75 PSI in the tires of his Jeep Cherokee. I thought the station owner was crazy to allow that because he said part of the reason he got rid of the shop air was that a couple of people exploded their tires with shop air.

So, the next time you are out driving (or posting on an internet discussion forum), look to your left and right. There is a very good chance that you are looking at a moron.

[motosan]

OK Guys:
I have been driving with my A/C both On and Off for few hundred miles, and I concluded that the A/C makes very slight difference on MPG.

So what's changed to make my M from 15.8-16.1MPG to over 18MPG? Is it because I cleaned my fuel injection? Well, I am going to bring my car to another dealership to check A/C's funny smell and lack of coolness, and I will ask the dealership to check whether my throttle body needs cleaning, too. If it does, it is likely that gas I put in my car is not as clean as it should be...

Will keep you all posted...

[Peahi]

Originally Posted by Mjolnir

The AC off won't increase the gas mileage that much. But you may want to try my method. I use a long straw from an empty Pixie Straw and blow bubbles in my gas tank. It aerates the gas and I noticed a 23% increase in my gas mileage. Just make sure the Pixie Straw is completely clean because you don't want sugar in your gas tank.

I hope you don't do this out in public at the gas station. This is a great example of internet science.