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The country has seen lots of temperature extremes in the last few years, it is happening right now. Long winters have shown us what can happen to our FFH's mileage and some have devised ways to help optimize the mpg's, like engine block heaters, foam in the grill openings, covers in front of the grill, etc. This last two weeks has been extremely hot where I live, in fact, yesterdays 'worst weather in the US' cartoon on The Weather Channel website was my small town - HOT. Those of us in the hot areas have not written as much about our FFH's mpg's during hot weather because that threshold is pretty high. Our HVB's are cooled by bringing cool air from the inside of the car and blowing it over the HVB. This only helps when the car is in motion with the A/C on, parked and sitting in the sun the entire car heat sinks and the HVB gets very hot. I saw 108F on my FFH's dash outside temp display yesterday, inside my garage it was 100F. From personal experience and from other posts here the heat really starts dropping the FFH mpg's at around 95F and gets exponentially worse as the heat increases. Yesterday's driving had the ICE running under load most of the time charging the batteries, powering the car and A/C - our 22 mile trip in the afternoon showed only 29 mpg's. My last tank of gas netted 33 mpg's, pretty low. When us early adopters first bought these cars almost two years ago that mpg range used to confuse (and irritate) me, why does it get 50 mpg sometimes and only 29 mpg's at other times? We've learned and know the HVB is less functional in temperature extremes, it's the nature of the beast. Now I understand why this phenomena happens and just ignore it, the weather will change. - Side note: My brother lives in Palm Springs where summer temperatures above 115F are not unusual, his VW Golf TDI does not get these extreme mpg ranges.