Purchased 2020 Honda Insight Touring in July 2020 and was getting around 48 to 50 MPG average, then November came and temperature dropped to 60 degrees Fahrenheit (from 80-90), my MPG dropped drastically to 37, now it's about 20 degrees Fahrenheit and I'm getting 34 to 35 MPG. My driving hasn't changed. Is this normal? I called my service department and they said it was because of fuel additives they add during winter. My old Prius never had such a noticeable change, maybe 1-3 MPG difference.
I even tried 93 octane, but that made no difference.
I can't see any fuel entries on fuelly, are you using the cars computer read out or measuring the fuel economy correctly? The cars computers can often be inaccurate, although from experience, the Honda I had was highly accurate in fairness. See how your tank averages out, perhaps the reading is a short term figure, maybe resetting after each short journey? Have the nature of your journeys changed at all? Because hybrids can be awful on long highway stints, and are far better around town with lots of regen and low speed EV miles. I remember a review of a Yaris hybrid and it got similarly poor fuel economy when driven long distance on the motorway.
I created an account so I don't have any data on Fuelly yet. I'm using my car's readout but I also calculate with Trip A meter of miles over how many gallons I fill up at the gas station and the numbers are confirmed.