There is a monster diff between summer and winter regarding MPG. When its 85f and sunny im getting 55-60 mpg depending on driving habits, and when the temp goes to 30f i get 45-50, and when the temp is in the sub zero or single digits i drop as low as 35 mpg. Still better than the 17 i was getting with my pacifica but a big diff overall for temp change. as far as mech aspect, it runs a little rougher in really cold weather but then so do i !!

(Originally posted to HCH Forum; copied here when that thread was closed)

It hasn't been a very cold winter here - I've only driven the car in sub-zero weather on two occasions since I got it on 06-Jan - but I'll pass on my observations thus far (for the record: Burlington, Vermont has about the same climate as Minneapolis - so not as cold as, say, Duluth).

First, from an FE standpoint this car isn't any worse in the cold than any non-hybrid that I've driven (Pathfinder, various Subarus, Volvo...). I've been tracking my mileage in the Pathfinder for years, and I know that I'll range from ~17 mpg in the winter to ~21 mpg in the summer. If you figure that I'm getting ~48 mpg in the HCH right now at 30F, and that I'd be getting about 18 in the Pathfinder, that puts me on target for ~56 mpg in the HCH come summer (applying the same 3/18, or 17%, increase). This seems reasonable when I look at what people are already getting in the warmer climes. (It also says I'll probably drop a couple more mpg if we ever get 'real' winter temps again). That kind of difference (a 10 mpg drop vs a 4 mpg drop) satisfies the naysayers, but they're not doing the math (and sometimes just conveniently ignore that 4 mpg drop on the non-hybrid altogether). Because when you do that (the math), you'll find that as you apply higher-percentage drops to the hybrid and non-hybrid (ie reduce each by the same percentage), the hybrid actually looks like a *better* deal than it did before you applied the reduction. So don't let the big 'absolute' numbers turn you off.

Mechanically, all I can say is that most things mechanical do not like the cold, and this one is no exception. By that, I just mean that the **** things don't go as fast or as easily as you want them to go. On the plus side, it does seem to warm up faster than my other vehicles (and I don't mean idling in my driveway ).

Much has also been made in these forums about how Auto-stop doesn't work for the first 5-10 minutes of driving. That is true, but as my first full stop on my way to work doesn't usually come until 45 minutes into my trip, I'm not bothered much by that.

One other point about snow - I've said this before, but I just haven't seen a big FE hit when I'm driving on snow. This doesn't surprise me though as most people slow down from 60 to as low as 40-45 when it's really bad, and it just seems logical that the decreased wind resistance offsets the increased rolling resistance.

I noticed a slight drop in FE (in my AWD FEH) as the weather got cooler, dropping from average daytime highs of 60+ down to the lower 30s. The difference was maybe a couple of MPG (say, from 32 down to 30). Then when it got REALLY cold (for us), with daytime highs only in the teens, there was more of a drop, down to maybe 27 mpg. The FEH does seem to act a bit differently when it is VERY cold - the ICE (internal combustion engine) doesn't shut off as often, and comes on again after being off for just a short time. It seems as if the batteries aren't holding as much charge (I've heard this is an effect of cold), perhaps only 1/2 as much, so they discharge more quickly and the ICE has to come on. ALso, it has to come on more to keep the catalytic converter (and perhaps some other parts, I'm not a motorhead) warm enough. And the engine seems to race faster under load, but that might be my imagination; when it's that cold my brain freezes and doesn't operate very well!

So far I haven't had the Prius in any extreme cold (below about 25), so I don't know how it will behave under those conditions. It does pretty well in moderate cold, daytime highs have been in the 30s - 40s, with some rain and slush, and I'm getting about 47.5 mpg so far on this tank.

You will definitely see lower mpgs in cooler temps, but still probably substantially better than a non-hybrid, similar vehicle (at least that's true of the FEH, our 4WD V6 non-hybrid FEH gets only about 17 mpg in the winter, so 27 is still better than a 50% improvement).

Also, with the hybrids (and their "instant" and "average" FE meters), it's more "painful" (at least if you get the hypermiler mentality) to leave the car idling to warm up the inside, defrost the windshields, etc., so it tends to feel like a colder ride (at least for the first 5 minutes). And the defroster itself (in the FEH) keep the ICE from shutting off at all, so that would decrease mpgs even more if you had to keep the front defroster running. Of course, that's only a factor when the ICE would otherwise cut off (at stops, and during low-speed driving) - if you're doing 55+ on the highway with no stops, the ICE will be running anyway.

I find temperature to be the single biggest factor which affects my Prius' fuel mileage. If it's 60F+, I'll get highway miles in the high 50's. If it's 30F or less, that'll drop to the mid 40's. City/Suburb driving is worse, because I usually drive shorter distances. By the time the car's warmed up, I'm done my errands. Still, I'd place the mileage in the mid-30's.

While the effects of temperature may be exaggerated in a hybrid, any car will react poorly to cold weather. I see the same behavior in my wife's Passat. If it's warm, I'll get around 25/35MPG. If it's cold, the numbers drop to 18/25.

I'm having mixed results in Maine with the cold weather. I'm excited to stay close to average - right now 32.5 lifetime and am back on an upswing (banned hubby from driving my FEH).

Extremely cold temps, high winds or the need to run the defroster decreases the time I'm in EV, and yes the power feels a bit sluggish when I hit the gas as compared to summer temps.

Have a new commute of 30 miles with the option of highway or secondary route. Generally I take the highway to work - mid-day traffic volume and will do 60 miles per hour. My mpg will drop about .5 for the total trip. My homeward trip is done at night on the secondary road, speed limit 50. I find I can get my .5 mpg back. (If only I could get myself to leave for work earlier than I already do, I'd do the local road both ways and improve mpg).

C&J the Gas Pirates

I'm the Captain of this ship and I have my wife's permission to say so.

Well... your salesman should say ALL cars are affected by cold weather... not just hybrids.

I took a hit in big time hit in FE when our great Canadian winter arrived in early December. I was getting about 4.7 l/100 kms before that. I am currently averaging about 6.2 l/100 kms. Our January weather has been just the opposite here in Southern Ontario. It has been just like spring and my mileage has returned to about 5.5. I have to thank George W. for not signing the Kyoto Climate Accord for keeping our temperatures (and pollution levels) unseasonly high!

This winter hasn't been too rough and hasn't hurt my numbers very much.
Last fall we bought a fireplace cord of wood to be sure. Looks like 90% will be stacked for next winter.

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT

It's not your imagination. Colder air is more dense, thus a given volume of air contains more air molecules at a lower temperature.