MPG seems impacted by heat and cold

[spidey]

So we are approaching 10K miles since Oct 08. We are getting 48.9 MPG over life of the car. During spring, less AC and no heat, we were getting almost 52MPG but once the hot/humid weather came to NC we have dropped back to 48.8. Not complaining but seems AC also impacts the MPG specifically during that first 5 minutes and we seem to be doing more of those short trips of late.

[JimboK]

Correct. Without climate control, fuel economy improves with temperature. Climate control in summer gives a small hit with highway driving, a bigger hit with city driving, and potentially huge with stop-and-go conditions.

[Sandy]

Mine last tank was 38MPG think because of all the short trips, everything is 1/2 mile or less

[Bob64]

A/C (both heating and cooling) takes energy to use, and that energy is generated with gas...

mpg also takes a hit from air density when cold, and a boost from hot air (less dense).

[a priori]

Originally Posted by spidey

. . . Not complaining but seems AC also impacts the MPG specifically during that first 5 minutes and we seem to be doing more of those short trips of late.

You may want to reconsider your use of A/C on those short trips, unless your car interior already is cooled. Also, when using A/C you may want to set the temp higher (say 75 or 76) and limit the fan speed instead of using Auto. Each of these steps saves energy! The first five minutes also is highly critical, so you could consider limiting the fan a bit more for those few minutes.

Originally Posted by Bob64

. . . mpg also takes a hit from air density when cold, and a boost from hot air (less dense).

And that humid Carolina air is even less dense. This helps, to a point: when the dew point is high enough to approach the ambient temp, the condensation formed on the car's surface can start interfering with those "gains" from lower density air!

[Shawn Clark]

Adding to the above, the battery is "happy" at roughly the same temperatures as the occupants. In mid winter the car is inclined to charge the HV battery to double green bars at times until it is up to temperature. There are some specific temp threshholds it targets (if I correctly recall what others reported.)

At some point the battery can get too warm and require cooling. I've not noticed this happening yet and don't know how the battery cooling fan sounds. But apparently it could also be counterproductive to try to be Spartan and soldier along at 110 F in the cabin.

The battery temperature mileage effect is one that conventional vehicles don't experience. It is pretty noticeable at times when the temps are at/below the teens.

[ETP]

Originally Posted by Shawn Clark

Adding to the above, the battery is "happy" at roughly the same temperatures as the occupants. In mid winter the car is inclined to charge the HV battery to double green bars at times until it is up to temperature. There are some specific temp threshholds it targets (if I correctly recall what others reported.)

At some point the battery can get too warm and require cooling. I've not noticed this happening yet and don't know how the battery cooling fan sounds. But apparently it could also be counterproductive to try to be Spartan and soldier along at 110 F in the cabin.

The battery temperature mileage effect is one that conventional vehicles don't experience. It is pretty noticeable at times when the temps are at/below the teens.

looks like our 100+ weather has died for awhile but I still drive with the AC off. Do you get some sort of warning if the battery is too hot?

[JimboK]

Originally Posted by ETP

looks like our 100+ weather has died for awhile but I still drive with the AC off. Do you get some sort of warning if the battery is too hot?

No direct warning. You might hear the battery fan cut on, though I've never heard it either. If you're really attuned to the car's operational nuances, you might notice a change like I describe here.

Pardon the cliché, but prevention is the best medicine. The battery can easily get to 100F+ after baking in the sun all day, and its large thermal mass makes it slow to cool (and warm in the winter). I have tinted windows, I use a sunshade, I crack the windows, and IMHO most important, I park in the shade when possible.

[JimN]

It has been reported that the battery fan sounds like a turbofan on a jet. I believe the car will turn on the AC automatically to cool the cabin to cool the battery. Yes, the car doesn't like too cold and too cold. It seems to run best in the 60's.

[Shawn Clark]

The temperature extremes at the battery also limit or prevent transfers to/from the battery as I understand it. (If someone here has better/more detailed information the please correct this.) When the battery control system is unable/unwilling to allow the HV battery to be used as intended, your mileage will tend to suffer as the engine will be on more. That is what I meant about it being counterproductive not to use the AC when it is getting very toasty in the cabin.