Accord Milage drops 2 MPG

[tc1446]

The last two fill ups have dropped from 34 to 32 mpg. I'm guessing this is largely due to heavy use of AC. Does this seem normal?
The car is well maintained and top tier gas is used, mostly Shell. I have no complaints and the question is mainly out of curiosity.

 

[Jetronic]

did the AC have more work to do lately?

It's getting warmer here, but until now my car just records lower and lower consumption figures. The engine likes hot weather, the air resistance is lower when it's warm, the oil is thinner at all times etc... But it's not been over 90°F yet.

https://www.spritmonitor.de/en/detail/780112.html

 

[AirgunSavant]

I had a 13 Sport and I got 34 mpg too on a few Florida interstate trips which was fantastic. But like clockwork when I went over 65 mph to 70-72 mph it went to 32 mpg.
But still great.

 

[Kuato]

Originally Posted By: tc1446
The last two fill ups have dropped from 34 to 32 mpg. I'm guessing this is largely due to heavy use of AC. Does this seem normal?
The car is well maintained and top tier gas is used, mostly Shell. I have no complaints and the question is mainly out of curiosity.


Yes. The compressor costs horsepower, making your engine work harder at the same speed. But it's less HP than required if you keep the windows open!

 

[Lubener]

Originally Posted By: tc1446
The last two fill ups have dropped from 34 to 32 mpg. I'm guessing this is largely due to heavy use of AC. Does this seem normal?
The car is well maintained and top tier gas is used, mostly Shell. I have no complaints and the question is mainly out of curiosity.


The a/c could have some involvement in city driving but on the highway, I would think that the use of the a/c would be offset by less air resistance when the windows would be down.

 

[Jetronic]

and you can't drop the interior temperature below ambient with thewindows open! nor can you reduce moisture.

 

[mooferz]

Higher air temperatures also tend to increase engine knock, so perhaps the lower mileage could be more a result of your ECU retarding timing as it is sensing higher intake air temperatures, or directly in response to the knock sensors.

 

[UncleDave]

Higher temps zap HP in an NA vehicle, and the compressor absolutely takes energy to turn.

These two things together will cost you HP and mileage as a result.

32MPG at 72 MPH with Ac on is pretty thrifty.

 

[bioburner]

I'll take the small drop in mileage for the comfort. My Transit sees almost the same drop with AC and a bit more drop when it lived in MN winter

 

[PeterPolyol]

If it's hot enough to run the AC compressor all the time you can almost be sure you're not getting the same ignition advance as you did in the cooler months.

 

[Linctex]

In my 2008 F150 4.6, I get better gas mileage at 60 mph with A/C on..... than I do at 70 mph with A/C off. It's an aerodynamic brick!

 

[Nick1994]

My mpg moves around all the time in my Sonata, I can't make determinations on each tank if it's gotten worse due to something or what caused it.

 

[Schmoe]

AC and perhaps your fuel. Now, refiners are pumping out more ethanol gas because of air regulations. Notice the pumps when they say "up to 10%" ethanol. You may be in fact getting 10%, which will reduce your mpg.

 

[steve20]

Higher temps zap HP in an NA vehicle, and the compressor absolutely takes energy to turn.

These two things together will cost you HP and mileage as a result.

32MPG at 72 MPH with Ac on is pretty thrifty.


ODD---isn't it---?
My 2005 Accord (auto) returns 35-37 with A/C on straight-shot trips to FL. I've been driving to FL for decades-usually stopping at the same gas stations each way.
Trips to Roanoke and back have seen 40.5 on occasion, but these are on E0 gas.
Interstate speeds approx 78 mph
Steve