FE in the WInter

Actually , all of your "hunches" are true, I work at Balise Toyota in Warwick, RI. I deal with these concerns from the beginning of November to the end of May.

All these points DO relate to relative fuel economy...another item that wasn't spoke is your emission monitors. When your Toyota is in degrees below 47 degrees the emssion monitors(charcoal canster, vacuum switching valves, ect) do not run, we commonly call them monitors and they will not read your emssion gases when it is cold, the computer has this type of "setting" due to these sensor being SOO delicate, cold weather will skew their readings. So if the computer is not consistanly reading from the monitors, the fuel economy will be slightly compensated also....

Has anyone ever gotten a State inspection/emissions reading and it did not pass due to the "monitors not being set"?....thats why!!! :smow:

 

My oven gets hot enough to bake cookies fairly fast too, but it doesn't stay hot without burning some fuel. A better insulated oven will require less fuel to stay hot, but it will still require some. The same thing is true for your engine. It takes a big slug of fuel to warm it up at the start, then a smaller but continuous flow to keep it hot (pulsed continuous: on, off, on, off, over time). In cold weather it takes more for both, even with your blocked grill.

Tom

 

First, air density does affect aerodynamic drag. At the speeds we drive, it's a minor issue. Other factors in winter driving are far more important.

Second, yes, air density changes with temperature. Cold dry air is denser than warm moist air. Barometric pressure is a direct measurement of air density, as long as gravity stays constant (I hope that's true in your area). Periods of high barometric pressure feature cooler temperatures and clear skies, while low pressure is an indication of warmer, stormy weather. This correlation is not coincidental. Small changes in barometric pressure are significant. As a pilot, I can tell you that aircraft performance varies dramatically from a cold winter day to a hot muggy summer afternoon. The same thing is true flying out of Denver. You get less horsepower and a lot less lift at low pressure (pilots like to call it density altitude).

As for folks in Denver getting better mileage, have you ever noticed how many speed and distance records are set at places like Denver and Mexico City; it's no accident.

Tom

 

Takes more energy to reach operating temp, yes. But his point is once you get there, it also takes more energy to maintain operating temp than it does in summer because the temp differential is bigger.

 

Another point, already mentioned by qbee42, (#4) is the drive train.

Cold weather makes all lubricants thicker.

In extreme cold, oil can become like grease, and grease can turn to putty (even solid), so there is more resistance. Military aircraft flying to the South Pole, need the have the lubricants for the control surfaces changed, from grease to oil, or they may freeze up.

This may be an extreme example, but cold does affect anything that moves. This would include the transmission, wheels, bearings, any drive shafts, etc.. Any belts or rubber become stiffer and less flexible.

The colder it gets, the more energy it takes to get, and keep things moving, simply because the resistance is higher.

 

Yes, the engine in the Prius is more efficient than those in ordinary cars, plus it doesn't need to idle just to keep running. The control system on the Prius will run the engine just to keep itself and the catalytic converter warm. If necessary, it will play with the timing to cause unburned fuel to be sent to the catalytic converter, just to heat it up.

Your assessment that the engine makes so much waste heat that it will stay warm is incorrect. No engine currently made is adiabatic, which is what you would need to not suffer from external cooling effects.

I will state some of the facts again, since they seem to be points of contention:

1) The Prius engine wastes energy warming up and heating the catalytic converter. It does this whether the car is moving or standing still. It wastes more energy in cold weather.

2) The Prius engine continues to waste energy during operation if needed to keep itself and the catalytic converter warm. During warm weather at higher engine loads, the waste heat from the engine will be enough, but at other times it will need to run just to produce heat. Cold weather aggravates this condition.

3) All automobile engines waste energy to stay warm. With a normal car, there is so much waste going on all the time that little more is needed. They still waste energy, it's just harder to notice it with all of the ordinary losses. The Prius engine, on the other hand, runs only when needed and is more efficient when running. This means it wastes less energy, and as a result, has less waste heat for staying warm.

4) The top priority of the Prius control system is low emissions, not fuel economy. Good fuel economy is a byproduct. This means that the control system will sacrifice fuel to keep the emissions low, which is exactly what it does.

Tom

 

Yea-we see it all the time in the shop. I had to explain this to a customer who had roughly 16,000 miles, he hadn't owned his car through the winter yet, he had kept up on all his services, ect.... It was about 21 degrees out. I explained this to him he thought it was B.S. so I put his Pruis on the techstream scan tool...and showed him his monitors were not running at that time...

 

gazz, if your route does not involve any stops or speeds low enough to incorprorate EV operation, then you can discount the engine temps for the most part. engine temps still play a part, but would be very small if all highway speeds.

in your case, if the above is true, then its mostly the change in gas formulation and higher density of the air...drag increases exponentially with speed... look at the difference in gas mileage from 60 mph to 70 mph... in some cases, it can be nearly 10 mpg. but the power needed to maintain those two speeds accounts for less than half of that difference. the rest is pretty much wind resistance

so in my case, commute speeds being mostly 35-40 mph... drag is less of a concern, engine temps, more...

 

:bump2::whoo::whoo::roll:ray2:....Do you need a job?!! I've got a bay next to me open....that is the MAIN FOCUS point that customers FORGET about with these cars

 

I have a question for ToyotaTech38026. If the car sits for 5 minutes or less when going into a store and the coolant temp never drops below say 165F, why does the car not stay in S4? When it drops out of S4, it requires the idle check(engine running then auto-shutdown while car is stopped) again. If the car is left powered on(in "Ready") it won't drop out of S4 until the coolant drops below 155F. I have found that just by leaving the car in "ready" will increase FE significantly by not having to needlessly start the warm-up process all over again.

 

Thanks. I imagine it gets frustrating.

Tom