When my dad drives his Prius without A/C, he can go a week until refueling (he drives a lot). When the A/C or heat is on, it only takes 3 days until he needs to refuel. Is this normal?
There are too many variables there to accuse the climate control system of entirely affecting the results, but yes, use of the A/C, and especially cabin heat, I've found, does reduce fuel economy. Not by half, though. I would imagine other factors are contributing more, such as temperature, traffic, route, actual miles driven, driving style (in a hurry or not?), etc.
welcome! that's a better than 50% reduction in miles driven, if he's driving the ams amount each day. i'm guessing your numbers are off, but if not, his car may have a problem. i have nevr seen more than a 20% reduction in the coldest weather, with the heat blasting. a/c uses less than heat, unless you're in a hot climate maybe. he would do well to start documenting his mpg's at fill up time, and tracking the daily weather.
How many miles is he getting out of a tankful? This might be a moot point, if that Prius has a gas tank bladder, in which case it's better to calculate fuel fill up volumes and distance travelled. Summer 2013, I managed over 620 miles out of a full tank of fuel in my Prius II (66.4mpg UK). The A/C was used on its lowest settings at least 33% of the time. We're having a very mild winter in the UK at the moment, so i've got 59.0mpg on my MFD at the moment. I have once seen 48.0mpg during prolonged sub-zero (or lower single digit) temperatures over here.
Always have run ours with the climate system on auto or manual and have seen little change in mpg either way.
