We are in our 1st summer after buying our used '07 in January, car now has around 70,000 miles. I had been reading how the MPG goes up in the summer but ours has gone down from 35 to 31 mpg. Use to be that after filling the tank we would see the mpg reset with a very high number and then adjust down the further we drove but now it resets with a very low mpg and creeps up to 31 mpg.

Is anyone else loosing mpg now that it's warmer? Another question I have is, when the engine is at idle, the mpg gauge is at zero, could that be producing the lower average? Seems to me that at idle the gauge should show high mpg and then drop down as you throttle up.

Thanks for your input.

 

Are you using your a/c? That could account for the drop in fuel economy.

When the car is stopped and the engine is running (or not), you are getting zero MPG. If the engine is on, you are reducing your average fuel economy.

 

I usually get lower fuel economy during warm weather. As ppgroup noted, the air conditioner takes a surprising amount of energy to run. That energy comes from fuel.

When you are stopped, the car normally turns the engine off and runs off battery, and the gauge normally reads at the 'bottom' (below '60') to indicate that you are not using any fuel. It stays there until the computer decides that the battery is getting low, then it starts the engine to charge the battery. With the air conditioner running in hot weather, it only takes a few minutes before it decides it needs to recharge the battery. How long depends on how much charge was in the battery when the engine turned off.

You will learn to trust the computer to turn the engine on and off when it is needed.

 

Don't forget to make sure you have "ECO" mode enabled! It tends to turn itself off in SO many situations, so always keep an eye out. Also, using recirc mode can keep the A/C from having to work so hard. Also, in manual climate control mode, I found that using a slightly lower fan setting in stop-and-go driving will keep the ICE from coming on as frequently.

You didn't say where you live. High heat and humidity do have an effect, but checking the above will help.

 

I have noticed the same thing. I live in AZ and over the last week or so it's been over 105 and it's dropped about 10%.

I have managed to keep it to 35-mpg, but it was getting closer to 38. I have also heard that if you don't run your AC in auto, that it doesn't run as much? doesn't make sense to me, but I may try it to see how it plays out.

The re-circulator really makes a difference so definitely use it.

Anyone tried a higher octane to see if it helps in the summer fuels?

 

The biggest variable I've found is Battery temp.

The battery cooling inlet is in the back deck in front of the rear center brake light. I have found that keeping my interior cool with good cool airflow pointing at the battery cooling inlet helps keep the battery cool, and thus allowing a more normal involvement of the electrical side of the drive system. When it is real hot out, you'll notice the car with not go into e-mode and also stays in parallel charge mode more than usual. Cooling the battery helps on both fronts.

 

My findings are the AC should pull you mpg down by .04% to .08%. The 4% would be temps in the low 80's where the 8% would be 100F degrees.

These figure estimates are from my state, Southern New Mexico, where the humidity readings are around 10% to 25% during the month of June. The lower the humidity, helps the AC to more be more efficient. Two notches of fan speed works best for me after the cabin has cooled off.