Lousy gas mileage from cold weather?

Corolla MPG drops in the winter too. The drop isn't as pronounced (or noticed without a Multi-Display available), but you still can't avoid the effects of winter.

Blocking the grille, using an engine-block heater, and limiting the number of short trips are the usual improvement suggestions.
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Hi Ex...,

My Saturn SL II would change from 28 mpg in 70 to 85 F summer weather to 20 mpg in 0 degree weather. What is that a 29% drop in mileage. Your Prius gets about about the same drop (27 %). So sounds normal to me. Of course in Chicagoland when the weather is down to 0 F we are all driving around at 50 mph, instead of 70, so the impact on the Saturn mileage might have actually have been worse.

The other thing people forget to do is to pump up their tires when the weather gets cold. A tire will drop 1 PSI per 10 degrees F. So, if you set the tires at 42/40 (recommended most often here on Prius Chat, to get minimum edge wear, and good mileage) psi, at 40 F, the tires will be down to 38/36 at 0 F. Even worse, if you have not checked them since it was 70 F (not uncommon!!) your tire pressures could be down to 35/33. And if you started at 70 F , at the driver's door recommended pressures they would be down to 29/27 PSI ! Which would account for about 1/2 of you mileage drop off right there.

 

All fuel injected vehicles experince a mileage drop in cold weather. The reason for this is due to the fact that cold air is much more dense than warm air, and the injection system richens the air/fuel mixture at lower temps to maintain the recommended stoichiometric point (ideal air/fuel ratio that renders the best burn).

 

Our Prius (We're in Eastern Montana) dropped in mileage as well, but I have to say that 30 mpg in the car is still better than 15 in the pickup! I do have to say that my hubby and I decided to get a heater when we can afford one. He has also talked about building a garage for my baby. for some reason my heater froze up this year....but that's a different issue. If you do block it, let me know if that helps!

 

Hi Ezw1,

I doubt that keeping the mixture stoiciometric is the cause of winter mileage reduction in a Prius. As the Prius can run up at a higher gear ratio, and use the extra engine torque that is the effect of the more dense mixture. Or in other words the car will downshift. I actually noticed that the other day while doing some highway Super Highway Mode driving out in 10 F weather. I could get 75 mpg while doing 55 mph, with 1314 rpm, in a well warmed up car.

The cause has allot to do with tires. Ever flex a piece of rubber indoors, then take it out in 0 F weather and flex it after its cooled? Big difference. Now multiply that by 8 walls on the 4 tires on your car. After 20 miles those tires will be warmed up but it uses allot of gas. If you get in stop and go traffic, you can feel the tires start to get cold and stiff again, in 0 F weather.

Besides that, each tire is acting like a pump impeller and pumping out all the snow and/or slush to either side. The tires are no longer simply rolling, they are pumping - more losses.

And above 40 mph there is more air drag, as the air density is much greater. I work near Ohare airport, and one of the main landing paths for the planes is just south of us. In 0 F weather the aerodynamic noise from the planes is so loud, it covers up the engine noise. It sounds like the air is being ripped apart.

 

EZW1,

Keeping the mix stochiometric isn't the issue as best I can tell. The throttle valve (and in most vehicles some sort of separate small idle control valve--not sure on the Prius) is there to control the load and/or to maintain rpm. When you have colder, denser air, the valve(s) pinch back for a given load. There are some minimum idle valve stops (at least on some vehicles) that would allow slightly more air in, but this is really small in the big scheme of things.

Vehicles take longer to warm up in cold weather and if memory serves they run richer on start up anyway until some threshhold temperature is reached. (You can smell it in the exhaust of nearly any gasoline vehicle.)

Colder denser air will cause more aero drag, but that is more of a highway speed issue.

With the Prius the key weather difference I've seen is that the engine runs to supply heat to the coolant and the cabin (via electric heaters and coolant). This results in the ICE running much more than it would otherwise...especially when stopped or at low speeds in town.

 

Do what John suggested (blocking grill, EBH). You'll see a huge difference, guaranteed. Blocking the grill costs about $2 and can bring your mpg up by 5+. Heck, I blocked my grill and went from 45-47 mpg in 35 degree weather to 52.5 mpg. The EBH eliminates most of the nasty winter warm up cycle, too.

 

I'm currently at 33 mpg this tank, but what's even more frustrating than the mediocre mileage is that I am down to 6 pips on the fuel gage (have been since mid-70's on this tank). I may not get much over 200 miles on this tank. Last tank was under 250. I KNOW it only takes 8-9 gallons, but I'd still like to see even winter tanks get at least 300 miles.

 

ya, doesnt matter what you drive, the percentage drop in mileage is the same.

i live in the "normally" mild pac nw. where winter usually consists of rain, over the past 4 years i average just under 50 mpg in the winter. temps usually in the mid 40's or so...

BUT,

in the past two weeks we have had more snow than the last 7 winters COMBINED... temps in the teens... it really sucked. no snow tires, having to start car, run it for 5 minutes while shoveling snow off the windshield etc...

ok. that ended last Friday. now if that weather was still going on, i probably would have posted a 38 mpg tank... thankfully, my tank is now improving and you can see from my sig, the last tank suffered as well, but will still be lucky to hit 42 mpg...

so all in all, YES, weather greatly affects your mileage

 

Here in Cleveland I've always seen a significant drop in winter mileage (about 5 to 8 mpg). But it still gets much better mileage than my previous car (Pacifica), so I'm still happy.

Just out of curiosity, has anyone quantified how much of the loss is due to:

- Winter gasoline formula
- Engine staying on longer to maintain heat
- Denser cold air producing more aerodynamic drag

Since my mileage is lower for both long ans short trips, I'm just curious to know what's the major cause.

 

I checked my Volvo s40's mpg today with temps 19-25 degrees and 26 miles driven around town...usually get 20-23 mpg...today 17.
My 2009 Prius in good weather without AC running gets 48-54 mpg with the same type driving...yesterday it struggled to give me 45 mpg. So about a 10% drop for the Prius and more than 10% drop (I know, unscientific) with the Volvo.
My point is that all cars, even Priuss and Volvos suffer in COLD weather.Hopefully the local frigid temps (8-15 lows and 23-28 highs) will pass soon. You members up north have my admiration and sympathy.

 

Like all of you, I too have experienced a drop in mileage on my G3, IV (8500 miles now).

Today I filled the tank (the ICE was already at operating temperature)(and, it was below freezing outside), I drove non-stop for 140 miles, then re-filled the tank. l calculated the mileage at 50.2 mpg, which is down from my Summer mileage, but much better than my normal 44 mpg thus far this Winter. The ICE cycled on and off normally; it turned off at stop lights; and functioned completely normally in the hilly country in which I was driving (on the HSI screen, the ECO "light" was off going up hills; the display showing "99.9" going down with the ICE off. Between 35-45 mph the ICE functioned exactly as I become accustomed to during the Summer.

The experience convinced me that come Summer, the mileage will again return to over 50 + mpg. The Winter problem, at least in my mind, is frequent, short trips; the ICE running more to warm to operating temperature, and to maintain engine and cabin heat. I know that commuters drive basically the same route and distance Winter and Summer, but I do not. We are much more prone to make short, quick trips to run errands in the Winter.

 

i 2nd the grill block and if necessary, i will 3rd the grill block.

http://priuschat.com/forums/gen-ii-...nother-grill-blocking-thread.html#post1034229

 

Keep your tire pressures up. They go down the colder it gets. I'm down to 42 mpg last tank in cold weather from 50 mpg summer. Should be around 45 mpg; have to check my tire pressures again vs the Fall.

 

Mostly #2 and #3. The closest anyone has come to quantifying, AFAIK, is Wayne Brown. He discusses it here in terms of changes in energy usage. In addition to the ICE running longer, he includes other factors (thicker lubricants and stiffer seals) in defining "mechanical" energy increases as the area of largest increase for his sample scenario. The sample is for 65 MPH, so at slower speeds where aero drag is reduced, the mechanical component makes up an even larger proportion of energy requirements.

There are many variables here in addition to speed: whether the grill is blocked, whether an engine block heater is used (both of which I recommend as others have), the actual OAT, how much one runs the heater, the length of one's trips. Worst-case scenario -- and this is where the effect of a cold ICE is huge -- is a frigid morning start (like the OP deals with) with no block preheating, short trip at slow speed with cabin heat running full blast.

 

This Arctic weather has finally beaten my MPGs down below 40. I just can't make it to work and back without running the defroster. Once it gets back to just "cold" I think things will improve...

 

Also I might add that regeneration is limited in cold weather too. The frozen battery simply won't take high amounts of juice going into it. This decreases the benefits of regenerative braking.

I've noticed that at my current temps the amps going in seem to be limited to ~50amps no matter how hard/fast I brake.

 

I have noticed the same drop in mileage with the cold weather ...I experimented by using the power mode and driving within the eco range, trying to avoid going into the red zone ...seems to make a difference in performance and milage over just eco mode ...any one else try this?