A cold front just hit Dallas. The morning commute's temperature went from an ideal 75F to 50F. Even with the engine warmed up after a few miles, the colder air and wind seem to be taking it's toll. Seems like I've taken a 10% to 5% hit on fuel economy.

Curious to hear other members observations about the cold weather hit on fuel economy....

61.5mpg lifetime - 82mpg in recent months

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"fanatic" is what the lazy call the dedicated

Well, i doubt 50F will do anything. At least I don't notice any difference until we are near freezing or below freezing.

You'll see a clear hit..even at 50 degrees and worse the colder it gets. A review of the mileage database here and you can see the milage differences at various tempertures...look at my 73 tanks for a good example as we have relatively wide temp swings here in SW Missouri.

Evan E. Fusco, MD
'04 Prius/BC moded to the T
'06 Highlander Hybrid Limited AWD w/NAV

I've never underwstood the cold temperature mileage hit, can anyone enlighten me?
With conventional, non-hybrid ICE cars, lower temperatures generally increase engine efficiency, at least down to temperatures lower than 50 F. One reason is that colder air is denser, and thus more oxygen is sucked into the combustion chamber at lower temperatures. That effect of course is much more pronounced with forced induction engines like my former supercharger MINI Cooper S, which - like most FI ICEs - had an intercooler. On a dyno, you can clearly show the effect of the intercooler. Of course, without the compression, there is less of an effect.
All that aside, why is a hybrdi drivetrain less efficient at colder temps, when the ICE itself should be more efficient at colder temps. Is it merely the longer warm-up time?
For that, the difference between 75 ad 50 F should be negligible.
I remain puzzled.

Yeah,WHY does the mpg drop?Is the atm pressure that much higher when it gets colder.I really have never taken note of that,but I'm pretty sure I have never heard of a 33" hg reading-it is normally about 29.9" here in NO.Cool air is heavier-has more drag,but the differences are kinda small-maybe 2-3%(29.9 up to 30.2) and drag is usually less than 1/2 of the forces that must be overcome.
Why??Yes,the CAT CON has to be brought up to temp with a rich mixture,but that still doesn't seem like enough.Is it something to do with the regen braking-??Thanks.Charlie

well your engine doesn't reach optimal temp as quickly... is problem number 1.

But at 50F your engine should heat up pretty quickly and now the denser air is actually better for combustion (power).

There are many reasons for cars not achieving max MPG in the colder months...here are just a few to ponder...

Car engines must warm up to a certain operating temp before they most efficiently use the fuel. Winter months and colder temps make that transition from cold start to most efficient take a little longer.

Winter formula fuels used in most states hold less energy and this also hurts MPG.

Generally speaking, colder weather in many areas means "rain, snow, or slush or ice" on the roads - these things add additional resistance which the tires must push out of the way to contact the road, so they hurt MPG in that way.

Tire pressures also are lowered by the cold. Most people fail to properly inflate their tires all year, but ESPECIALLY in the winter when it is cold and you might have dirty tires and you just dont want to deal with spending time in the cold airing up a dirty tire. Low tire inflation can add quite a bit of rolling resistance.

Additional idling uses fuel, and many people in cold climes are used to warming their car up in the morning. That is good practice to stay warm, but BAD for MPG numbers. While idling, your car is getting 0 miles to the gallon !!

People who use the defroster in a Hybrid are many times using the A/C compressor to help reduce the humidity in the car and clear the fog. That is a MPG killer too.

See this science page for more explanation:

http://www.sciam.com/askexpert_question.cfm?articleID=000BBB5F-0CF9-1080-8CF983414B7F0000

Hi All:

___Colder temps increase your tires RR by a huge margin, increases frictional losses in all rotating parts, allows some of your fuel charge to pool against the cylinder walls of a very cold block, and a colder then normal coolant temp tells the ECU to richen up the mixture. All either prevent the most efficient combustion or increase friction. Colder temps as in a CAI are great for HP down a certain temp but are worthless for FE.

___My ride home in the Accord this morning in a miserable 45 - 51 degrees F temp makes it **** hard to maintain what would normally be a walk in the park. 51.2 mpg to my place of work last night with every trick thrown her way. She now sits with a lowly 48.9 with a low of 48.1 on my way home this morning Above 72 degrees and all is great in the FE department of just about any automobile. I have seen hits in any number of automobiles at ~ 62, 52, 45, and 32 degrees F. Below that and the best you can expect from your automobile will be simple survival for lack of a better term …

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

It's good to hear form xcel as he has had experience on a number of hybrids. xcel, you are in good company this weekend. Hal Hidgon, who has done 111 marathons, is an expert on running economy (a runner's body behaves a lot like an IMA - future thread). The Chicago Marathon this weekend is possibly the fastest/easiest because it's almost completly flat.

I expect the first few miles to have relatively poor fuel economy, as the engine and the cataylic converter are warming up. What suprizes me is noticing a harder time past those 1st few miles keeping the instant mpg readings over 75mpg (when the 5-speed Insight is in the lean burn mode). My guess is colder weather inhibits lean burn. I would not be suprized if lean burn never activates in sub-zero weather.

61.5mpg lifetime - 82mpg in recent months

Best Run >
www.cleanmpg.com

"fanatic" is what the lazy call the dedicated

Hhmm, I'm still a little sceptical.
Yes, warmup time, and more than that, winter fuel, should produce a mileage hit.
Rolling drag I'm less sure about. The increased ICE efficiency resulting from denser air normally more than makes up for that. On my MINI, cold temperature FE greatly increased, before winter fuel use started, and by about a whopping 15-20%!
Even in summer time, I don't see any mileage hit in wet vs dry weather (in terms of water on road) unless it is positively pouring, then yes.
I think a good way to test this would be to sequester some summer fuel in a barrel, and then use that in winter time to see what FE in winter, with summer fuel is like.
Now, if I can find a barrel somewhere, and a hurdy-gurdy...