First few minutes mpg

I have not done any investigation but notice that when I drive the three blocks through my neighborhood first thing in the morning to let the engine warm up, I am only getting about 20 mpg and using the battery.

When I get to the main road where I have to merge with 45 mph traffic and have to accelerate, the ICE will kick in the mpg will jump up to the 40 mpg range as you note.

 

See Ken@Japan's sticky thread in Gen3 Technical Discussion forum on warming up stages of the 2010. He discusses this very point, as well as a reason you may choose not to accelerate hard, and his alternate solutions.

 

Any time you draw energy from the battery you will see better short term mileage figures. This is because the mileage meter does not include battery charge in its calculations. In effect, what you are doing is borrowing energy from the battery which must be paid back later, with interest.

The instantaneous mileage looks better, but the real mileage is lower.

Tom

 

in the first few minutes of operation after extended parking time which would be first trip of the day from home or coming home from work, i have very very little options as to my driving style, speed, etc.

i have a child almost 3 (most common age for child involved in pedestrian/auto accident) , live across the street from the park and despite a posted speed limit of 20 mph, we frequently see people driving much faster.

but then again, this is another of those "i get better mileage at 65 mph than at 55 mph" thread by another name

and logic, rules of physical laws, etc. did not work on that thread and probably wont work on this one either

 

Good point. Well put.

 

There are two problems with this approach:

1) The ICE is not as efficient when cold.

2) Driving hard with a cold ICE draws more energy from the battery.

The lower efficiency would be immediately obvious if instantaneous mileage were calculated from gas consumption *and* battery drain. Unfortunately the instantaneous mileage only looks at gas, so you don't see the real cost of forcing the ICE to run harder.

This is a common mistake, and often it encourages new Prius owners to try and maximize electric only driving. Since the instantaneous mileage gauge only looks at gas consumption, driving in electric mode shows infinite mpg. It looks really impressive on the mileage gauge.

Unfortunately, the electricity from the battery that is being used has to be replaced. This comes at the cost of burning gas. The efficiency of burning gas to make electricity to charge the battery to make electricity to power an electric motor is much, much lower than burning gas to directly move the car.

Tom

 

This is said without full comprehension how it all works, but when the ICE is running - let's say you are driving at a constant 50mph on the highway, isn't the ICE always still charging the battery still, and isn't some of that charge wasted? Or are you saying that the ICE will temporarily run at a higher rpm to charge the battery that you just slightly or moderately discharged minutes before?

 

I try to avoid it because if the ICE is cold, the emission is higher. The catalyst converter is cold too and it will not operate best. The result is more emission goes out the tail pipe and you also waste gas.

For emergency situations (pull out to incoming traffic), you need to accelerate hard. One way to avoid it is to warm up the car in advance until you are out of stage 1.

 

No. The ICE does not charge the battery for free. Any charge that goes into the battery is using more fuel.

There are situations where energy would otherwise be wasted, such as braking. You can think of this as free charge, even though it originally came from burning gas.

Tom

 

Were you driving at the same speed seeing 20 mpg and 40 mpg?

My assumption is a warming up fuel consumption is based on seconds(time) per gallon instead of miles(distance) per gallon.
If you drive twice of speed, you'll see double instantaneous mpg on such condition.

Ken@Japan

 

For those of us who don't understand much, like me:

Is it better to drive reasonably gently during the warm-up period, so you don't have the engine being VERY inefficient at high revs
or
(if you have the choice) is it better to drive reasonably briskly (as some Toyota literature puts it) so as to warm the engine up more quickly
?

Or is some other driving pattern best during warm up?

Thanks.

 

Drive gently during the warm up. At this stage the Prius is mostly running on battery power and using the ICE to make heat. If you drive briskly you are forcing the ICE to carry the load before it is ideally ready.

Tom

 

My recommendation is stand still or gentle driving during S1a, then drive normally later S1b and other stages.
http://priuschat.com/forums/gen-iii...-discussion/76501-gen3-warming-up-stages.html

Ken@Japan

 

i warm-up around 3 mins atleast every morning, and i see around 10-20 mpg 5-min mileage, then i get about 40-50, and the third sometimes as high as 75 or more. clearly, the warm-up stage (where ICE kicks in in normal mode) uses lot more fuel as one would expect.

i'm close to emptying my second tank, and i'm only slightly better than the first. so far,i'm about 38 mpg compared to the first tank of ~36mpg

 

warming up the car while idling is not a good idea either. granted, i do it but only because i have to spend time scraping windows, etc. but i dont feel that you benefit from this.

in my situation, its pretty much 20-25 mph for the first mile or so since i am in a residential neighborhood. in 10 months of ownership, i have just passed 8,000 miles so dont drive the Pri a lot and about 90% of the driving over the past 3 months has been my 7 mile work commute. i think my work commute does well simply because

1) speeds max 40 mph (sometimes faster in the morning if "need" be but never over 45 mph)

2) i have a gentle drive for first part of commute on both ends.

3) warm weather.

now, if not for the warm weather, i would be around 46-48. i am at 50 mpg, so the weather is contributing to at least 2 mpg.

 

If you limit your warming up to 1 minute, you should see an improvement, because the warming after S1a (see Ken's link) is pure waste of fuel. Get it moving at that point.