Is 39.1 MPG Normal?

Hi Culture...,

If your driving in 0 to 5 F weather, like we have had here near Chicagoland the last few mornings (warming up now, but with lots of black ICE), 39.1 is about right in a new Prius. I drove my car from the dealer home in 15 degree windy weather (head and side winds) and got 43 mpg on that 384 mile trip.

Things you can do to help the mileage, is be sure your tires are at 42 psi in the front and 40 psi in the back, and run the heater at 65 F defrost. After running down the road for 5 miles or so, assuming you have clear glass, set the temperature control on AUTO and 65 F. Then push the DEFROST button (top row all the way to the left). The temperature will still be in feed back mode at 65 F, but the automatic climate control will not be functioning. That is, the dehumdifying functions, and automatic up down selection of vents.

 

+1 on Tony's comments back in post#19:

In my experience, seasonal temperature variations is the largest long term
variable affecting MPGs. (Daily traffic volume is most significant in the short
term.)

Chasing high MPGs in the winter is hard work, especially if you're a new
owner... I know, I startred in Dec, last year. Chose one of the tricks that
would seem to be appropriate in your particular driving environment. Work
on it until it is second nature. Then add another. In cold temps it takes work
and time to get good results. It is important to remember that someone
else's 50+ MPGs is applicable only to their unique individual experience, a
sum of temps, terrain, traffic, training, equipment, -- Block heater? Grill
block? EV switch? ScanGauge? etc.

I found it helpful to determine a rough way to predict what would be a
challenging MPG expectation each day as I stared my commute. For my
particular conditions this formula is a good predictor of a very good MPG
result on a 28.8 mi. round trip commute:

MPG = Air temps (deg F) + 1/2(60 - Air Temp)

So, for air temp = 30 deg: MPG= 30 + 1/2(60-30) = 30 + 15 = 45

(You'll be surprised how quickly you can learn to do the math in your head.)

So, if I come home at 40 MPG, I'm pretty happy because I know that winter
blend fuel carries a 3-5 MPG hit.

This exact formula might work for you. It will take ten days or so of driving
on your daily drive to see -- expect daily variations due the pesky traffic.

If it does't work, fiddle the 1/2 factor up or down as needed. Keep the result
high enough that it represents a real challenge, not a cheap gimme.

And for heaven's sake, relax and have fun as you learn.

Hope this helps.

 

Good MPG short-path zen:
- Accelerate briskly (this uses the engine most efficiently; izza2me, you may be driving too gently).
- Drive as though you have no brakes.
- Gliding (no arrows on the "Energy" display) is better than coasting, coasting is better than braking, braking is better than stopping.
- *Never* use "B". There's no call for it in Florida.

It might seem a paradox, but the *less* you can use the battery the better the MPGs will be. All conversions of energy from one form to another are less than perfectly efficient (that is, some of the energy is unavoidably turned into heat and lost), and batteries are especially poor.

 

Richard,
Interesting points those. Two seem counter-intuitive:
1) Why "accelerate briskly" as opposed to "starting off from a dead-stop very gently" OR "accelerating from slow to quick speeds very gradually"? It would seem that in the former, you would definately consume more gas because of the higher engine rpm's whereas in the latter, you would "optimally" consume gas "efficiently"

2) Why "less you can use the battery the better"? I mean, is this always true? I'm not so sure because the battery provides energy which is representative of (a) gasoline-energy and (b) mechanical/regenerative energy. Hence using battery power would always better than pure gasoline power

 

I really wish dealers selling Prius would give a buyer a free fill up then allow them to drive their old car for a tank before replacing it with a Prius. The dealer could then refill the car and tell the new Prius owner what they got out of their old car for that tank and compare that to the EPA listing. Then when we ask a person complaining about bad fuel mileage "what did you get from your old car, not what did you think you got but what did you actually get?" they might answer!

Here is my driving style in a nutshell.
I accelerate at 2/3 throttle when I can.
I hold my foot steady at 2/3 until I get to the speed limit and only then lift off.
I use the minimum throttle I can to cruise, try lifting your foot slightly.
I speed up 5 to 10km/h over the speed limit when approaching a rise, then hold the throttle aiming to drop to the speed limit by the top of the rise without moving my foot. This isn't for mountains just rail overpasses and the like.
I allow my speed to rise going into an underpass then drop on the way up to exit at the speed limit.
I try to pick my route to travel in free flowing traffic.
I try to pick my route with steeper climbs and long down hill runs. Yes I come home along a different route to the way I go to work.
I lift my foot when I see a red light ahead. I don't race up to red lights.
I try to time lights so I don't have to stop. Once you get moving keep moving.
If you have to stop try to lift off early enough that the car almost stops before you need to brake. If you get this right you will only brake under 8mph. This is hard to do, I have only managed it 3 or 4 times.

Other than the above I just drive my car and use 4.3 to 4.4 L/100km. I don't live where it is stupidly cold but it does get stupidly hot. I avoid the AC when I can be comfortable without it. If I can be comfortable with the windows down I wind them down. If I need some air I put the fan on especially if I am driving over 70km/h.
I'm a fat little bugger so I like to keep cool, if I need to I will use the AC.

Cold weather would have knocked around your mileage in your last car too.

Energy in the battery ultimately came from the gas engine. It came from gas, became kinetic energy, transmitted to the generator or the wheels, then either turned into electrical energy in the generator or preserved in kinetic energy in moving the car or lost as resistance (heat and noise). For the energy to get to this point it has had all the losses along the way that a gas car would and there were losses in the generator to heat. Then there are losses in the inverter, and further losses in the battery as the energy is stored as chemical energy. Some of the kinetic energy moving the car may now be recaptured by regenerative braking but there are again conversion losses, however this is energy that a conventional car would waste as heat.
Now to use this energy we stored in the battery we have further losses converting to electrical energy from chemical, from electric 200v to 500v in the inverter further loss then converting that to kinetic energy.
You can see the path from ICE to wheels has far less places to lose energy than by sending that energy through the electrical side of the system. If you minimise the use of the battery electricity you minimise those loses.
I hope that makes sense.

 

Sounds a bit low, but not unreasonable for winter with a car you really haven't checked out fully yet. Winter gets us as mentioned. 70 mph tends to fall in a range in the high 40's for me in more comfortable weather...and lower in winter so far.

Winter stuff: Consider grill blocking. Consider an engine block heater. Be reasonable in your use of heat/defrost. These force the engine to run more than it would otherwise, especially when the AC must run for defog/defrost. Folks here can give you good winter tips for climate control to provide comfort without waste.

Car set up issues: Tire pressures (as mentioned.) Oil level (dealers often overfill and this often hurts mileage.) Might want to verify you have appropriate oil installed for winter. Alignment--if it is out the vehicle may pull one way or another hurting aerodynamics, increasing tire friction, requiring more steering input, etc. Brakes dragging somewhat--reported occasionally.

Driver issues: Learn to use the brakes as little as possible. Learn to rely on the traction battery as little as possible--you don't want to pull/accelerate with it so much as gently "glide" with it to extend ICE off time. Accelerate briskly with ICE (but without pulling from traction battery if possible.)

 

it's in the 20's and 30's here and i drive it like a normal car, 80mph on highway and i still get 43mpg. i haven't driven in a week or so, gas is cheap so i drive my tundra crew max around all the time. god i miss the 5.7l engine. everyone is so worried about mpg's. it is a car people. drive it like a car. the only reason i bought one was incase gas hit $5 or above. now that it is cheap i think i will park my 08 prius. it is small and slow. overall it is ok, but i like to have some power when i step on the gas.

 

Internal combustion engines are most efficient near their maximum output. It's a little hard to judge that point without a scan tool, but roughly, if you're accelerating faster than most other cars that's about right. Flooring the gas pedal is too much, and if everyone else is accelerating faster than you it's too little.

The Prius is not a plug-in hybrid, so essentially all of the energy in the battery ultimately originates from burning gasoline in the engine. All energy conversions (chemical <-> mechanical <-> electrical) involve loss. The more you can avoid using the battery the less energy will be converted and the less of it will be turned into useless heat.

So why does a Prius have a traction battery at all? It's to avoid the efficiency penalty of having an internal combustion engine sized for acceptable acceleration, because an engine that big is much too large for good efficiency while cruising (the point about engines being most efficient near their maximum rated output, again). The benefit of using an electric motor to provide low-speed torque (a regime in which the engine is not efficient) is so large that it overcomes the losses of the energy conversions into and out of the traction battery.

 

When the Prius first came out in 2001 the initial indications were that most people were trying to make it a gas-assisted EV vehicle. That is that they tried to get the battery and e-motors to try to do all the propulsion.

In fact the Prius is not in any way an EV vehicle, at least here in NA. It's a gasoline-powered vehicle with an electro-mechanical assist.

Your goal, if you choose to accept this task, Mr Phelps is to get the ICE to get up to temperature then to try to turn it off as much as possible.

The key that was found by the Gen 2 hypermilers is to get up to speed as quickly as possible within reason then glide / coast as much as possible in order to use no propulsion at all, neither chemical nor electrical. The initial Gen 1 buyers determined to use the potential EV properties to crawl away from a light or stop sign. The Gen 2 hypermilers found that this was too strenuous on the system. For the little extra fuel used to get smartly up to speed using little or no battery power the ability to glide / coast made up for it. [ Note: nobody beats me away from a stop light ]

Even moreso there is a basic physical property that cannot be overcome by any vehicle. Newton's first Law of Physics. Essentially as regards to the Prius it suggests - DO NOT STOP!! Having to overcome the inertia of being at rest is hugely inefficient. Just keep rolling, seriously. Of course you have to be safe and you have to follow the law but here is a real world example from my time driving in NYC.

Going across town from Avenue-to-Avenue, block-by-block, being stopped at every light on every block I recorded an average FE of something under 40 mpg at about 25 mph. Turning south and going downtown at a constant 25 mph gliding as traffic slowed I recorded 70 mpg!!!

Both results were back to back in moderate weather.

Get up to speed quickly and then do as much as you can through your brainpower to avoid having to come to a dead stop.

 

very true. my mileage generally sucks because:

1. i have very short trips (about 10minutes or less)
2. my trips are not only short they involve many stops (lights and stop signs), with little opportunity to actually keep moving at a consistent rate of speed
3. cold weather.

as a result of 1 and 2, even in summer, I struggle to reach low 40's only occasionally hitting 47 or more when we go further and there are minimal short trips to and from work. Because of all 3, in the winter, I get low 30's when weather is particularly bad and up to high 30's or even 40 when weather gets better AND drives get longer and less stops.

I've also found that when I move too gently my mileage suffers, better to quickly get to a reasonable speed and keep it there with as much gliding as possible. The time to be gentle is when slowing down, and try to slow early in hopes that you won't even have to stop... although vehicles behind you never seem to get that part of it.

 

Sounds like we have the same commute! out:

 

Richard/DeadPhosh,

I see your point about engine size <--> efficiency. But really, what *is* the point of the battery/motor and how best to take maximum advantage of it?

It seems that
1) While starting from a dead stop, it's best to accelerate at "normal" speeds (= speed of traffic) because a slow 'crawl', even if entirely propelled by battery, is not as efficient as a complete ICE propulsion

Therefore, it is best to avoid the battery here

2) At cruising speeds upto ~35 mph, your ICE is most efficient but you also obtain *added* propulsion by the battery (= glide), which in turn results from mechanical --> electrical --> mechanical energy conversion. I guess this is where the bulk of the hypermiling (= 'prius-like' fuel efficiency) comes into play.

If so, the battery provides provides the key advantage here and you'd want this assist as much as you can (energy losses notwithstanding).

I would also guess that this is the differentiating factor (with respect to propulsion technology) for the Prius compared to conventional cars.

3) At hwy speeds (40-60 mph), you have a situation similar to (2) above, I guess..

I'm just trying to make fundamental sense of the battery/motor portion of the drivetrain (vs. the ICE both in Prius and conventional cars) with respect to enhanced fuel efficiency

 

"Glide" = no arrows on the energy display; in other words the battery is not being used. One can learn to do this with a little practice by using a light touch on the accelerator and glancing at the display.

That exhausts my advice. Beyond this the hypermilers can offer theirs :_>

 

Richard,
I know you are exhausted but I learned on another thread that GLIDE = a single arrow from battery to the motor and COAST = no arrows on MFD.

Here is the link to this discussion - could you please clarify?

http://priuschat.com/forums/fuel-economy/57220-technicality-hypermiling.html

 

That definition is just wrong. Gliding = no arrows. Coasting = foot off the gas, auto regen occurring.

 

i noticed that when the temp is low, mid 30's-low 40's, the prius on the freeway is not super efficient. that's just the way it is. i recently took mine on a trip, from LA to San Francisco, averaged about 70 mph..........even though ALMOST EVERYONE was going 80+ and i just about averaged into the 30's in mpg.

the prius is an AWESOME car in the city, it seems to be rather short legged in such trips.

 

That poster was mistaken. He retracted the error on 09 Jan.

 

Ah. The Atkinson cycle used by this engine is fuel efficient but has poor torque at low speed, so the electric motors compensate for that. The car would get even better fuel efficiency if there were no battery assist for acceleration, but the acceleration would be unacceptably, even dangerously, low (think of getting stuck behind some idiot on an onramp). At highway speed the engine is in its comfort zone and battery/motor assist adds little to fuel economy. Conventional cars use an engine cycle that gives better low-speed torque but poorer fuel efficiency.