I've been dealing with crap fuel economy all summer. I had tested a bunch of theories, including cleaning the throttle body, the MAF sensor, I used fuel injector cleaner, took my custom tune back to stock, checked my air intake, changed my oil, etc. Even thought it was linked to increased ethanol in the gas.

 

It seems kinda dumb in retrospect, but I never checked my A/C because it was functioning perfectly inside the car. Well this past week, temp and humidity dropped to the point that I turned off the A/C and to my surprise, my fuel economy immediately shot up. I actually turned on the instant MPG display and watched the number drop when I clicked the A/C button on and off.

 

Sure, everyone knows A/C reduces fuel economy slightly, but after driving on a fresh tank of gas with no A/C usage, I've gained 3 miles per gallon. THREE. Now my average is right where it's supposed to be. I've owned the car since new, I've never had the A/C hurt mileage worse than winter blend gas.

 

Wtf is going on? Is there some maintenance I should perform on the A/C compressor?

Make sure you have enough refrigerant in the system, if it is low, the compressor has to work harder and longer just to keep the same level of cool.   It could be as simple as that. 

Thank you. The car is old enough, I hope that's the case.

On a similar note, it could be wonky compressor bearings. Either way, probably age-related.

I would agree with Drew, maybe try one of those AC recharge bottles that are like $15 at an auto parts store.  At least then you'll know the refrigerant is full and not leaking, and the AC working the right way.  A car should still get better fuel economy with the windows up and AC on, vs all the windows down and AC off at highway speed.  Drag should hurt fuel economy more than the AC.

 

Also might want to check tire pressure, that could affect fuel economy, maybe new air intake filter if you didn't change it already, those are like $20-30 usually.

Tires and air filter are fine (c'mon, that's basic maintenance! I'm insulted!).

 

I am getting the trans serviced soon, I'll add A/C recharge to the laundry list.

turn it off

Yeah... Roll down the windows and enjoy the real air. 

 

I never get that. Every time I can my windows are down. I hate A/C for the most part

Yeah... Roll down the windows and enjoy the real air. 

 

I never get that. Every time I can my windows are down. I hate A/C for the most part

Keep in mind for a person that has allergies to so many things, AC and the filtered air it blows is a relief from the attack on ones nose. Sadly my daughter was fine till 13 and with the change that comes in a young woman's body, her body decided to make her allergic to many of the outside items and foods. So now a strict diet along with a dread of spring and fall when things rapidly change has her use AC with filtration so she can drive around without her nose and body reacting horribly.

 

One of the best things ever was auto's with filters for outside air and the AC to keep one comfy on hot days.

Yeah... Roll down the windows and enjoy the real air. 

 

I never get that. Every time I can my windows are down. I hate A/C for the most part

 

Yeah, but you're from MD too, you know that mid May through August is non-stop A/C season. I'm not putting my windows down when it's 85-95 degrees and humid like a sauna.

I agree with them. It is most likely age related.

 

Yeah... Roll down the windows and enjoy the real air. 

 

I never get that. Every time I can my windows are down. I hate A/C for the most part

 

Yeah, but you're from MD too, you know that mid May through August is non-stop A/C season. I'm not putting my windows down when it's 85-95 degrees and humid like a sauna.

 

Same here in the mid west. It gets brutal hot and humid from june-august. This august we had a SUPER mild streak though, like a week and a hald of 80 degree highs and 65 degree nights. It was amazing.

If it is 85/90 degrees and a very high dew point the AC will be working hard constantly as well. In Iowa the dew point was in the 70s to  low 80s and it was often 95+ degrees when I lived there. This is horrible working conditions for an AC system. The food plant I worked in actually would need to shut down production if the dew point reached 80 as the ammonia based cooling systems could not longer operate efficiently enough to keep things cool.