Why does it get worse MPG in cold weather?

Poke around the forums here a bit, you'll find countless discussions on MPG drops in winter. The short answer is twofold, it takes more energy to bring the hybrid components up to optimal running temperature when it's very cold out, and winter gas is actually different and less efficient that summer gas. Many folks have had good luck with an engine block heater, but there's not much you can do about winter gas.

But most importantly - you can turn off the reverse beep so it stops driving you batty. Instructions can be found in your manual, or in countless threads here.

-Ken

 

One of the reasons is consuming gas for warming up.
A good solution is to install an engine block heater.
http://priuschat.com/index.php?showtopic=11176

Ken@Japan

 

First the beep look in the manual there are instructions or do a search here.
The second is both easier and hardier. There are many ways to increase your milage in cold weather. Ethanol will not help it has less energy per gallon than gasoline. First blocking the radiator works but you may want to get additional instrumentation to monitor engine temperatures. Before you do that I would try a block heater to reduce the warm up. Find the best routes that means slower under 40 if possible. You are fighting the cold, and winter gas. It is a up hill battle and no matter how good you get at driving your car you will find you get better milage in the summer than winter but you can raise both. Look around on this forum, performance mods forum.

 

Among the reasons

Longer warmup time.

Engine cools faster requiring more running to keep catalytic converters up to temp.

Warm up of any kind uses richer mix burning even more fuel.

Increased oil viscosity and gear lubricant viscosity.

Fuel Atomizes poorly in cold weather, resulting in less efficient combustion.

Decreased battery capacity and response.

Lower Tire Pressure (unless you check regularly)

Increased Rolling Resistance (increased energy to flex less flexible sidewall).

Increased Rolling Resistance (rain/slush/snow).

Colder air is Denser meaning more wind resistance. For every 10 degree F drop in temperature, aerodynamic drag increases by 2%

Winter Fuel. (Lower Energy per Volume)

Higher Auxilliary Electric Use (Headlights, Defrosters, Defoggers).

I'm sure there are more, that's just off the top.

 

This may be a silly question, but do ALL cars get lower gas mileage in winter? I never kept up with the milegage on previous vehicles. My Prius mileage peaked at 57 in the fall and hovers around 48 to 50 now in winter. Also (and this may be off the subject) am curious about the snowflake light on the dashboard. Not much is said about it in the owners manual.

Thanks,
Bonnie

 

All cars suffer MPG hits in the winter, for most of the reasons Tempus listed. Lower energy gasoline, and lower overall system efficiency in the cold hits all cars.

Only the Prius gives you the sort of instantanious feedback that makes it obvious. And Prius drivers are far more obsessed with MPG, and more likely to notice. Thus, it tends to get tossed arround as the Prius's Achillies heel, which is just silly.

For example, when I was tracking it, my saturn got 33/26 during the summer, and 25/19 in the dead of winter. (20's - 30's F)

And a friend of mine with a SUV averages 16 in the Summer, but only 13 in the winter, which while it is only 3MPG, is a 20% drop.

-Ken

 

If you're getting 5-10 MPG less, that's about right. As has been noted many times, most non-Prius-driving folks don't know how bad their winter MPG is because their car doesn't tell them.

 

Now that's a good question. In my past cars, I'll use my 2002 Audi A4 Quatro as an example, mileage varied very little over the year. Throughout the year I held about a 25.8 mpg average.

I believe the primary factor in reduced winter mileage in the Prius is battery efficiency. Virtually every aspect of a battery suffers as the temperature drops. Haven't you noticed the gasoline engine doing so much more of the work when driving on those cold winter days. You can hear it .. You can feel it.
But don't take my word for it, go to google and enter batteries vs. temperature. There's a pretty healthy dropoff in charging ability, storage ability, and current released on demand as the temperature drops.

 

Sorry, but our data does not show such result.

A Japanese enthusiast used to get 70MPG on his 20 mile commute these days.
(Yes. his environment and technique are very good.)
He installed an engine block heater and got 83MPG data at the same temperature range and it's almost as same as his best in good season.
There is no condition change around battery, only change was heating the ICE by the block heater.

Ken@Japan

 

The Prius changes its battery use strategy in cold weather to mitigate the effects of temperature on capacity- on my Classic, I can see that although it limits battery use in cold weather, it also maintains a much higher SoC in the battery (I'm usually driving around at 63-67% SoC in the winter vs. 58-60% in the summer).. Now of course, if you hit stop and go or slow routes that require battery use and the SoC dips below 56%, the car becomes a real pig because the charge current is limited to the ballpark of 30-35A instead of its usual 55-60A, but in "normal" conditions, I feel the car is actually *more* efficient and responds better in this mode due to the higher average SoC..

I would love to be able to fool the computer into switching into "winter" mode during the rest of the year so I could test out the effect of the winter charge management algorithm with higher BTU summer gas.. I've also been using Shell V-Power for the last few tanks and notice a consistent mileage gain vs. the Esso 87 that I usually fill up with, in fact, in combination with my "minus-sized" winter tires with better rolling resistance and the Shell gas, except for the start-up hit, I've been averaging *better* than my usual *summer* mileage.. I do have my radiator blocked off, and I wait until the coolant temperature has reached at least 50C (the temperature it switches out of "warm up mode") before I turn on cabin heat (otherwise it takes almost twice as long to get to 70C, where engine stop and stealth are available)..

 

Unless you have a scanner which shows you the coolant temperature you should not add any air dams or insulation around the radiator and engine. Prius is not a farm tractor; it does a very good job of establishing and maintaining its own optimum engine operating temperature. Interfering with that system creates a risk of chronically running the engine (or localized spots on the engine) too hot, which reduces MPG and may damage the engine.

Reduced MPGs in cold weather is basic physics, and it happens to all cars. The single best thing you can do to deal with it is to check tire pressures at least once a month, or whenever the average outdoor temperature changes by more than 20 F or so.

 

look at my sig... i think you will find that normal... we have very mild winters here. average temps are mid to upper 40's and low 50's. colder areas will see a larger swing towards the low 40 mph range. that is normal. even with several refinements, mid 40's is best you can hope for.

i know its a let down when most of the summer you blew away the EPA average... but yes, all cars do the same thing... revel in the fact that the guy across from you at the pump is there twice as often as you and probably paying twice as much per trip

 

I don't think much has to do with the battery. The real question is how does your Audi manufacture the energy missing in winter gas to get the same mpg in winter?

The battery is used less in the cold, but this affects you not getting 65 mpg instead of 55 at slow speeds.

Has little to do with winter mpgs going 55 to 45. But don't forget trip speeds and lenghts play a major role here. Prius gets pretty good mpg in winter too on any trip over 45 minutes at highway speeds, and the battery will warm to cabin temps and work normally too.

I get lousy mpg in winter from short trips. But any reasonable trip lengths with a warm car I can get summer mpg just corrected for the fuel change and the air density change. There is no unexplainable extra loss of mileage.

Trips even at 0 deg can still get mpg's in the 50 and up mpg range. The only thing I lose is the super mpgs up towards or above 70 mpg going at 40 mph or less. Engine doesn't generate enough heat for this.

My normal commuting is only 10 miles or so, so day to day I do less well but my mpgs this winter have stayed up above 48 mpg so far. So I don't consider that bad. It is way better than my previous car did in winter.

 

We had a heat wave in Tennessee this weekend--temps climbed to mid sixty degrees. My MPG rebounded as well. It's back up to 53 mpg.

 

Wait a sec, c4, you've got undersize tires on it for winter? Do
you expect to see anywhere near the same mpg *accuracy* in that
case? If they're spinning faster to get you there in the same
time, no wonder you're seeing a higher MPG figure.
.
_H*

 

ya but that wont account for the disparity between the MFD and the mighty pen. inaccuracies created by wrong sized tires will translate to both numbers

 

Some of Tempus' explanations are definitely right and others are at least plausible (I'm not an automative engineer). http://www.fueleconomy.gov/feg/factors.shtml mentions lower energy content in winter gas. http://www.cartalk.com/content/columns/Arc...7/March/01.html also talks about some factors.

I personally have noticed somewhat worse gas mileage in the winter on my regular cars.

 

Hobbit-

No, they're not undersized, in fact they're a full 3/4" greater diameter than OEM.. What they are is "minus width", compared to my summer tires.. I have a Classic, so the OEM tires are 175/65R14. I've "upgraded" to 185/65R14 Hydroedge for the summer, but I went with 175/70R14 X-Ice for the winter.. The tires are narrower for better snow performance, but greater diameter, both of which contribute to better rolling resistance.

In any case, your logic is backwards- if the tires were smaller diameter, yes, they'd spin more to cover the same distance; more spinning for the same distance = more engine revs for the same distance = *lower* miles per gallon.. In my case, the tires are larger in diameter and spin *less* revs for the same distance, and that translates into *higher* miles per gallon. However, even counting the 4% difference in revs per mile, and another couple MPG for better rolling resistance, I'm still doing better than summer mileage, therefore my only assumption is that the additional difference is coming from the Shell gas that I've been using recently..

 

Not pimping Sunoco but their website has some good information with numbers: Sunoco - TRANSPORTATION FUELS.