I have a 2005 Audi A4 2.0T (I guess that makes it the 2005.5 model). Anyway, I bought this car CPO about 8 months ago. During the fall and winter, I drove the car in economy mode almost the entire time (e.g., no air conditioner working). During that time, I averaged about 20 MPG.

Just recently, the weather got hot in Connecticut, so I started driving with my air conditioner on. I have driving through 4 tank fulls of gas, through a variety of city/highway driving. Now that my AC is on, I am consistently getting 25 MPG (a 25% improvement in my fuel economy!). I do not have any degradation in performance that I can perceive. The car seems to drive equally well, regardless of whether the AC is on or not.

Does anyone have any ideas what could be happening??? At face value, this defies all logical sense (and all mechanical principles). Has anyone experienced this before?

I spoke to one Audi service dealer, and the guy was a complete moron. His only recommendation was to drive with the AC on all the time. Seriously. What a freaking idiot. This clearly seems like a problem with my vehicle that needs to be resolved. I can't imagine that the 2005 A4 was designed to achieve a higher fuel economy WITH the air conditioner on! Right?

So I've come up with a few ideas about why this could be happening. I was hoping to get some feedback/thoughts on other suggestions. Has anyone else experienced this?

One idea: the fuel in CT could change with the seasons. I know that some areas put a more oxygenated fuel into the pumps during the winter. Now that summer is here, perhaps the fuel has changed and I'm getting better mileage? (of course, that would mean everyone is getting better mileage as well). As an aside, I have almost always bought my gas from the same Mobil station that is located 2 blocks from my house.

Another idea: when the AC turns on, that may be doing something weird to the ECM. In turn, that could cause the wastegate to close more than it needs to. So I might actually be driving with less turbo and perhaps a higher fuel economy. Maybe?

Thoughts? Experiences? Any and all are welcome!

Thanks!

 

Actually, that is correct. Cars are built to be driven with all windows closed and the air on. The old axiom of A/C making worse mileage went out in the early '90's when cars started getting more aerodynamic. Opening windows destroys that, causing drag which kills mileage. Kinda like opening a door on a plane.

Now, a 5MPG difference is rather large....but possible.