Average milage fell from 40 to 35 overnight
 

I got my 2018 ES300h in late August and found that I was getting a very stable 40mpg both in city and on highway. It rarely fluctuated more than 1mpg in either direction. Now, for the last month I've been getting a very stable 35. Tire pressure is fine. Gas from the same stations - 87 octane top-tier. I have 9k miles.

Any idea what might cause this? It was not a slow and steady decline - it was always 40 until it was always 35.

Thanks

Many brands of fuel begin switching over to "winter" blend which vaporizes more easily (perhaps at lower
temperature also) to aid with cold weather starts. "Summer" blend then is better at limiting pollution by
not evaporating as much in hot weather. The timing of your experience might be partially explained if
this occurred at your station. Never have seen a sign or notice at the pump to announce the switch over.

The other reality is that you are very likely using the lights, defrosters, seat heaters and driving speeds a
bit differently than last summer. The fuel injection compensates for cold starts with a richer mixture for
a bit longer also. All contribute to decreasing your mileage. Be happy that your "h" gets 40 rather than
the 25 MPG of the 350. Someone with an ES350 should chime in and relate how much reduction you
have seen on screen!

In addition to the above, fuel efficiency, by itself, is reduced when the temperature drops.

Mpg is not optimized until the engine reaches its normal operating temperature. When the temperatures drop, it takes longer for the engine to warm up and fuel economy drops. And fuel economy can take its biggest hits when you are doing lots of short trip driving because, after each short trip, the engine cools off, and, when you start driving again, it has to warm up all over again. Further, I would guess that, in colder weather, the ICE is being used more than it is during warmer periods.

I have no idea what the temperatures have been in North Carolina, but, in the states with more severe winters, mpg can drop by 25-30% or more during the coldest part of the winter. Even if North Carolina winters are not nearly as severe as those in some other parts of the country, winter temperatures that are colder than during the other seasons will still have a noticeable impact on your fuel economy.

I would bet that, next summer, your fuel economy will return to the same level as what you experienced last summer.

The hybrid also has to run the engine more often in winter to keep coolant, engine components and emissions control parts warmed up. I usually get 45-50 mpg in summer city driving whereas in winter, I get 35-40 mpg only.

Thanks, everyone. I assumed that summer in the Carolinas would be bad since the AC runs non-stop but that's the danger of over-simplification.

My 2013 ES300h has dropped as low as 32 calculated mpg per tank of gas over the last 2 months do to cold weather here in Georgia. Usually in the winter it drops to 34 mpg.

2018 ES300h mileage graph
 

https://cimg7.ibsrv.net/gimg/www.clu...b3a894e872.jpg
When you reset the MPG in the Driver Information Center (between the Speedometer & Charging/Tach) by using the
steering wheel "White Dot" button it adds a column to this Navigation Screen. Note the dates, we try to reset at or
around the four seasons. If the car does not have Nav you see the same graph but it does not display the date BTW.
This is for Chicago and we drive 80% city and 20% highway.

Data is beautiful.:cool: