Cold Weather Performance

Oh you *had* to bring THAT up, didn't you??

Seriously, as far as "performance" the Prius is better than conventional cars in very cold temps. Although my condo has heated underground parking, I've parked it outside a few times at my hobby farm.

Even not plugged in, at -40 it starts instantly, which is very impressive itself. The electric assist is also available to provide immediate power. At temps colder than -25 C, most cars are very sluggish.

Cold is just not a problem as far as basic car performance goes. Now that I've got 16,000km on mine, I'll switch to a synthetic motor oil. Next winter I'll either run a synthetic 0W-30 or 0W-20 to ensure reliable -40 performance.

Performance on slippery road surfaces is another matter entirely. The Trac is *very* sensitive, so even in conditions where mild wheel spin is beneficial, you're going nowhere. Some Prius owners have commented on great traction on snow/ice even with stock tires.

I finally slapped on some Dunlop Graspic DS-2 winter tires on steel rims. With those tires I can easily blow the doors off a 4x4 at a green light.

The fuel "loss" means the bladder inside the fuel tank will shrink with cold temps, so you can't put in the rated fuel capacity. I like to keep my tank topped off in cold temps to avoid fuel icing problems, also in case of an emergency a full tank can save your life.

Jay

 

Sid -

"Also, I'm unclear about the fuel tank bladder loss of 5L. What does that mean?"

It's been said that the fuel tank will shrink; well, here is the technical reason. In the case above L = Liters.

In the world of physics there is a phenomenon known as thermal expansion and gas law.
An object will change in linear length and volume with a change in temperature.

For the equation below we will use metric (because imperial sucks!):
beta (of gas) = 3 x 10^-4 C°^-1
Volume of expansion: (delta) Volume = beta x Volume x (delta) Temp
Tank capacity: 11.9 gallons = 45.046 liters = .045 meters^3

So, if you were to fill up your tank at 10 degrees C and the temperature drops to -10 degrees C:
(3x10^4)(.045m^3)(20 degrees C) = 2.7 x 10^-4 meters^3
You will "loose" .27 Liters of fuel.

Or you will loose .0135 Liters of Fuel for every degree C change of a lower temperature.
Of course, if you fill up when the temperature is low you will gain .0135 Liters of fuel for every degree C change of a higher temperature.

It should also be said that the density of air is higher at lower temperatures, which means your Prius will have to work harder to "push" through the thicker air.

 

Besides the gas itself shrinking, the bladder itself shrinks, thus causing it to hold less volume of its contents, which in our case is gasoline.

 

I sure hope we don't have to drop a couple of FloMax tablets into the tank at every fillup.

 

Between having taken that photo and the 5 winters in Minnesota with a Prius, I think I'm well qualified to answer the question.

The battery-pack likes the cold. Keeping cool is of no concern during those harsh winter months. So the electric side is actually favored more when in comes to power than in the summer... believe it or not.

Startup is a snap... something traditional cars can be quite jealous of, since their motors & battery are so tiny in comparison.

Speed is a non-issue. You can effortlessly maintain 70 MPH for hours on end. But you really don't want to. Pushing through that dense winter air using the less efficient winter-formula fuel pushes the MPG down. But then again, that's true for all vehicles.

Getting heat is surprisingly fast (of course, it's like cheating having that thermos). The system does a really good job of retaining it too. So you can still drive in stealth at times.

 

John:

I find in city driving in temps colder than -30 C, the ICE has to run constantly. When I leave my heated condo parking in the morning, the first red light it will shutdown. The next light around 3 km down the road and it stays running.

Now that the temps are +25 C and warmer, it readily goes into stealth at slower city speeds.

Jay

 

In the frigid temps, Does turning A/C on and full recirc keep the cabin warmer or does this still create too much moisture on the windows?

 

At -30 C and colder any use of recirculation will almost instantly frost the windows. Running Max Heat at -40 C still requires mitties and a hat.

That's my biggest gripe to date with an otherwise great car: you freeze your a** off at -30 C and colder. There have been numerous posts regarding this too.

 

<div class='quotetop'>QUOTE(john1701a\";p=\"92343)</div>

There is a report by NREL on preheating of batteries in HEV:

Cooling and Preheating of Batteries in Hybrid Electric Vehicles

I believe Toyota has done an excellent job in Battery Thermal Management as can be testified by various owners that do not have problem in harsh winters. But saying battery-pack likes the cold is something I find it hard to comprehend.

Vincent

 

<div class='quotetop'>QUOTE(vincent1449p\";p=\"92852)</div>

The chemicals inside definitely favor the cold for longer life. Heat accelerates aging. So cold is always the preference.

As for performance, you made the same assumption most people do. They find out that capacity is reduced and come to the conclusion there isn't enough to fulfill typical operation. But in reality, there is far more of a surplus available that the reduction isn't even detected.

Don't take the generic on-paper info to literally. I have a ton of experience with this with Prius itself in those conditions. It is very obvious that greater motor power is used when I leave my house and climb out of the valley every morning on the way to work.

 

With the ICE running nonstop, does the battery get used less in these cold conditions as well? Since there'd be no stealth or engine starts, I figure the battery used less until the engine warms up, more like an assist. I've heard reports of batteries being green most of the time in very cold weather, since the ICE is running so much just to make heat. Should the ICE warm up to where it could shut off, by that time the passenger cabin should be warmer and the traction battery as well, no?

I haven't experienced conditions cold enough for this sceanario myself, but does this seem like a reasonable explanation for the good performance in the cold (along with surplus capacity?) I've read NiMH chemistry is less affected by cold than lead acid, and for storage they prefer ~5C, which minimizes their standby loss.

 

<div class='quotetop'>QUOTE(gschoen\";p=\"92991)</div>

Trust me on this: in winter city traffic with the temps at -25 C or colder, especially down towards -40, the ICE will *never* shut down. For Jan and Feb my battery was almost always fully green.

The vast majority of Prius owners don't live in such bitter cold conditions, so it truly has to be experienced to be believed. I still wish Toyota could run supplemental electric cabin heat off all that excess HV battery charge.

My Prius actually feels *stronger* in extreme cold temps, probably due to the excess charge. With my winter tires on, I have no problem blowing the doors off 4x4's when the light turns green.

 

<div class='quotetop'>QUOTE(john1701a\";p=\"92867)</div>

I think you have missed my point.

The purpose of that paper is to present the importance of Battery Thermal Management in HEV. Without it, HV batteries will suffer in driveability, fuel economy and life at extreme cold or hot temperatures.

That's why I said Toyota has done a wonderful job in overcoming this limitations.

Vincent