"YMMV", but by how much?

The variation is normal, and is controlled by the physics of driving and the vehicle. Warm-up is a fixed overhead. It costs you the same on a short or long trip, but on a long trip the cost is amortized over more miles. Cold weather driving consumes more energy for warming the engine, supplying cabin heat, and overcoming rolling resistance. High speed driving incurs much greater aerodynamic costs.

There isn't much you can do about any of these except avoid them. Perhaps a block heater is the exception. All cars suffer in the same way, only with normal cars mileage is so poor that you don't really notice the difference. Going from 19 to 15 mpg is hardly noticeable. Going from 50 to 40 mpg gets your attention, even though both are the same percentage.

Likewise your traffic situation will make a huge difference in mileage. Stop and go is bad for mileage. So is warp speed. It's all normal.

Tom

 

Here's lots of data, in an easy to understand format...






And of course, I'm quite curious about what the 2010 will look like in comparison to the 5.5 years of data from my Iconic and 3 years from my Classic....




The thermal improves in the 2010 model should make this winter very interesting.
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One of my neighbors who is an electrical engineer at GM claims his GM cars don't suffer reduced mileage in the winter but I'm sure they do and as Tom noted, you just don't notice it as much in a non-hybrid.

Has anyone put a scan gauge on a non-hybrid and if so, do you observe the same significant mileage drop during warmup, especially in the winter? I'm assuming my Odyssey would show something like high single digits for the first few minutes but I don't own a scan gauge (yet).

 

With just a tachometer, it was obvious with my Taurus. As clear as day, you could see for the first few minutes (warm-up) the engine at a higher RPM.
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Yes, I've seen that on non-hybrids with a tach. In the dead of winter, not only does it start with higher RPMs, it takes longer for them to drop to 750 RPMs when at an idle. I'd be interested in seeing the mileage hit.

 

My Prism goes from 31-32 mpg in summer down to 27-28 in winter. Other factors may be involved too, such as gasoline formulation, etc.

 

Yup, with a ScanGauge-II installed in my Subaru a year prior to acquiring my Prius.

Well, the Suby's variation is not proportionately as large because its high end MPG is strongly limited by the large fixed-valve-timing engine with lousy gearing, and I refuse to coast it with engine off. But the overall pattern is very similar.

 

It would be easy to make a car that got the same mileage all year. All you have to do is add something to make the mileage artificially bad in the summer.

As silly as that statement sounds, there is some truth to that when it comes to perception. With human interface design, consistency is very important. It's better to have a system the responds at the same speed every time than have one that responds at that speed some of the time and faster at other times. Even though the response is equal or better in all circumstances, people will complain because sometimes the system is "slow".

Tom

 

Hi DetP...,

There are two things going on. There is the math/marketing/phsycology thing. The MPG will change more in a Prius but the percentage change will be similar. This is just because 10 percent of a 50 is 5, and 10 percent of 25 is 2.5 . This change is because of cold tires, longer engine warmup times, and higher air drag (more dense air). They are the same for all cars, although the Prius has a smaller engine than the same performance standard car, has less metal and coolant to warm up.


And as Gbee aluded too, the Prius does probably loose more percentage than standard cars, because, standard cars are wasting so much gas through the radiator that the Prius is not. In the Winter that wastage in standard cars is funneled into the cabin, while in a Prius, the engine runs more to make morw wastage in the winter so it can also be funneled into the cabin.

 

I used to get the same mileage 32 MPG in the summer and in the winter when I drove my 1997 Eagle Talon, but if the temps were higher then 70 I always ran the A/C. When the A/C quit working on that car the last 2 summers I had it the mileage magically went up to about 35 - 36 MPG all summer long and up past 40 MPG on a few of my longer trips.

 

I drove our auto AWD Subaru yesterday, and was wondering how much fuel is saved by neutral, either coasting or at a stop. Any ideas ? Opinions about possible increased wear on the transmission by shifting between neutral and drive while moving are also invited.

 

What year is your Suby?

If it's an OBDII car, then coasting in neutral is probably more wasteful since the engine has to idle. MOST OBDII cars do this thing called DFCO, or Deceleration Fuel Cut Off. Meaning, when you let off of the throttle completely while in gear, fuel to the engine (and spark) is cut. The inertia of the car drives the engine.

Thus, simply letting off the throttle and coasting in gear is better for fuel efficiency than shifting to neutral and letting the engine idle.

 

My Suby does a lot of coasting in neutral, but it has a manual transmission, making it a much different beast than your auto. The choice between coasting in neutral (no drag but some fuel burned) vs. DFCO in gear (no fuel burned but significant engine drag) is very dependent on the immediate situation, and both methods get considerable use. This car has a ScanGauge, which helps in making the choice.

More advanced methods are avoided because I can't shift and rev-match it as smoothly as the old worn Honda, and I want to get at least another 80,000 miles from it. The extra wear can be kept low with a stick, but I lack experience with modern automatics.