It just so happens at my place of work there's a lovely bunch of environmentally minded people who own Prii (sometimes you see 5 or 6 of them in the little parking lot, including one of
Wentworth's twin charcoal grey brothers or sisters). Now, most of them would fall under the umbrella that 95% of drivers fall under: they have to get places, and they need their car to get them to those places.
It's hard to remember for Prius enthusiasts armed to the teeth with engine coolant temperatures and doing mental math while driving to compute the requisite engine-off glide distance needed for a given mileage figure that everyone else in the world just drives, and many, including me at this point (though I'm learning!) have no idea what's even going on inside their engine.
Recently some of these people have made passing comments expressing interest about improving their mileage. This post is thus for the "beginner" Prius driver. Even if you've owned it for several years, if you don't know how to initiate an engine-off glide, for example, you will be able to learn a couple techniques to improve mileage by 5-10% at the very least while still driving "normally" with the flow of traffic. Since this is intended for anyone to be able to use, don't worry about any technical specifics - they're just fyi, but not necessarily relevant to general operational knowledge.
Please note that while most of this post is for general Prius use, some of the info and all of the pictures involved are specifically for model years 2004-2009, aka the Generation II Prius. If you have a model year 2010 or newer, please refer to
this link, which is a very good starting point, but not too detailed, and has the occasional easily forgivable minor information error.
I would suggest taking one technique at a time and learning to apply it quite well, and then learning another one. You want to feel comfortable enough to use it without having to stare at your multi-function display the whole time, mostly for safety reasons. So, onto our first technique.
Technique #1 - The Glide
What it is
This is a big one, the meat and potatoes of higher mileage in non-highway driving. In its very basic form, the Prius glide is a state achievable under 42 mph where the gas engine turns off completely while at speed. A very small, practically negligible current comes out of the battery pack to keep the car rolling a little easier than if you were in neutral, or more than a conventional vehicle rolling while off in neutral (don't try this at home, kids). The Prius glide is a built-in, perfectly legal function that shouldn't be confused with illegal neutral coasting in other cars. The fuel savings are enormous, as we'll see in a minute.
Preparation
A glide is only possible when the engine is properly warmed up. On a warm day, that might take you 3 minutes. In frigid weather, over 10 minutes. The other day in 27°F weather, it annoyingly took me about 3 miles. I remember once in 19°F weather it took well over 10 minutes, even with the heat produced from some highway driving.
It will also be easier if you have already driven your car that day, or just a few hours prior. The Prius has a thermos (like you may for your morning coffee) to keep the engine coolant hot/warm even outside of car use. When you turn your car off, it pumps hot coolant into the thermos so that when you turn on the car next, it can get up to optimal temperatures more quickly, providing the heat needed for the engine, electronics, and various emissions reductions systems. As an example, the other morning my coolant was very cold, around 30°F (outside temperature). I drove to work. I parked at 8:30am with coolant now at 177°F. When I left to go home four hours later at 12:30pm, the coolant, thanks to the thermos, was still easily over 100°F despite sitting out in 30s and low 40°F weather for four hours.
To provide a little extra information for the curious (though this is not essential to remember), there is one more requirement for a glide once warmed up. This next paragraph will likely be cause for mild confusion to the new reader, but I can assure you once you try it yourself it becomes simple to understand. If you're in the area I'd be happy to demonstrate.
The first time in a given drive that you warm up the car (at the start of the drive, of course), you will enter what is known as stage 3 operation. There is no indication on your display for the different stages, you just have to know what they are. During stage 3 in the Prius, you can only enter a glide when the speedometer reads 35 mph or higher, but not higher than 42 mph, as mentioned above. If you try to do a glide with the speedometer reading 34, even if you feel you're going 34.99 mph, the engine will just stay on. To get to the next, final, and most desirable stage, known as stage 4, where you can glide at
any speed under 42 mph, you must:
Allow the engine to idle for 5 to 10 seconds, and then shut down completely by itself. You can guess that this usually happens at a stop sign or stoplight. The moment the engine shuts down, congrats, you'll be in stage 4, and likely for the rest of the drive! Now you can initiate a glide at any speed under 42 mph, not just at or above 35 mph as in stage 3.
"Just get to the point already!" How to use it
On your multi-function display (screen in the middle), touch "Energy" if it's not already selected. Although it's fun and more user friendly to look at the bar chart on the "Consumption" screen, you actually need info from the energy screen to get the best mileage.
Normally when driving and accelerating your energy display will look something like this:
Or maybe this, if you're just starting up an acceleration:
Once you've satisfied the above conditions to enter a glide, simply lift your foot completely off the pedal. At this point you'll see this:
The blue or green arrows (which color depends on your model year, they mean the same thing) pointing into the battery indicate a state of regenerative braking. When this happens, you can easily feel that you're slowing down! To get into a glide, you want to conserve momentum, so jump to this next part quickly.
Push down ever so slightly on the pedal. You should see all arrows disappear:
You're now in a glide. If you see the following, though, you've pushed the pedal too far:
The yellow arrows indicate EV mode (electric vehicle mode), which is sometimes useful, however is not a true glide. Let up a bit to get into the no-arrows state you saw above.
Mileage
The glide practically, or at least for mathematical purposes, gets you infinite miles per gallon. Use it, use it, use it!
As a mileage example, let's say you have your foot on the gas for 0.3 miles with the instant mpg reading exactly 30 mpg. If you are then able to engine-off glide for an equivalent distance of 0.3 miles, your average for the entire distance is 60 mpg. If you glide for another 0.3 miles after (so 0.3 miles of acceleration or "pulse" on gas, then 0.6 miles of engine-off glide), you are at 90 mpg over the entire 0.9 miles. Not bad! This is, of course, almost never practical, and not safe in heavy traffic. But even without extreme use of glides, they will be notably beneficial to your mileage.
For a normal driver, without delving too much into the hypermiling technique known as pulse and glide (an example of which you just saw in the previous paragraph), you can use the glide on downhills, when coming to a stop, or even on flat roads in normal driving when you are content to just about maintain speed or there is a slower vehicle ahead of you but you want to avoid losing momentum by braking. Most Prii come with fairly low rolling resistance tires, and all have wonderful aerodynamics, meaning they'll roll a good deal just on momentum compared to other cars. Give it a try, see how far you can go when there's not any traffic behind you.
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Technique #2 - Warp Stealth
What it is
Warp stealth is a mode that allows you to cut fuel to the injectors while travelling at higher speeds. On a generation II Prius (2004-2009), the gas engine must run at and above 42 mph to safeguard the electric motor (46 mph on model years 2010-present). What this has traditionally meant is that the best mileage is only available under speeds of 42 mph, since only then is it possible to perform a true, high mileage-inducing, engine-off glide. Luckily, warp stealth (yes, it must have been Star Trek fans that devised these names...) allows you to at least slightly circumvent that problem on the highway, allowing for a sort of high-speed glide using no gas. While the gas engine must still spin at very low RPMs, usually around 960 or so, this is accomplished with a relatively small amount of energy from the battery - about double the energy of a simple glide, or the same power as running your air conditioner.
Warp stealth is best used on a slight downhill, or if you are approaching your exit. You will slowly decelerate with warp stealth, so you'll find if you overuse it on non-downhills, you may actually waste more energy trying to accelerate back up to speed.
How to use it
Luckily, the muscle memory required for warp stealth is identical to that of a glide. When travelling at a speed higher than 42 mph, simply lift your foot quickly off the gas, invoking regen:
Then reapply oh-so slightly, and instead of no arrows like a glide, you'll see yellow arrows coming from the battery.
You're now in warp stealth, using zero fuel.
Interesting to note that at these speeds, it is a rare occurrence to get no arrows like you would see in a glide, and while I've seen cruise control magically do this somehow (though the engine was still spinning, to be sure), you'll find that 999 out of 1,000 times or so you won't be able to do it - so don't waste your time :-)
If you slow under 42 mph in warp stealth, you'll see that somewhere between 40-42 mph the engine will cut out, and you'll be back in a glide, or perhaps electric mode if the pedal is depressed enough.
Mileage
Since warp stealth uses no gas at all (though some energy) you can use the same logic to calculate mpg over a given segment. If you are travelling along getting 40 mpg on a slight rise on the highway for half a mile, and then have a similarly long descent ahead of you, you would get 80 mpg on that overall segment. These numbers are not practical in real life, since you usually are unable to find such a nice downhill, but even if you only could use warp stealth for half the distance of the climb without losing too much or any momentum, you would get 60 mpg over the segment, a more realistic and certainly possible number to achieve. While I am a relative newbie to highway driving, with most of my driving in what the EPA calls "city" (in other words, just not the highway), I can offer a recent personal example, when I drove down route 24 from near Boston. Even with those pesky hills, my novice attempt at steady acceleration followed by warp stealth when possible yielded 58.5 mpg on the display over 51 miles.
If you are a frequent bridge traveler, as many here in Rhode Island are, use the backside for warp stealth all the way! No need to use any gas - gravity will pull you along very nicely.
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Technique #3 - Super Highway Mode
What it is
Another dramatically named technique you can use in certain situations at higher speeds. The engine and battery pack go back and forth with their energy use - arrows will be all over the place on your screen, so don't even worry about them. You can use SHM to maintain speed on a flat surface, or else accelerate very slowly on a downhill.
How to use it
The best place to test it out is on a flat piece of highway once you're already going your desired speed. Simply let up considerably on the accelerator, but not enough to enter into regen or warp stealth. At about 55 mph, it should be very easy to get the instant mpg at about 75 mpg. This is SHM. You'll be able to just about hold your speed if on flat ground at this very low state of fuel consumption. Even 60 mpg is a decent mileage to shoot for. You'll find that once you try to milk it and go higher than 75 mpg, toward 80, and eventually 99.9+ mpg, you'll be loafing, and will lose speed very easily. Maintain that momentum! It's better than slowing down too much and having to accelerate again later.
If you find that you're trying SHM on a slight downhill, and are holding speed just fine with instant mpg at 80 or higher, just switch to warp stealth, it's much more efficient than having the engine loaf in SHM.
Mileage
You'll have a hard time quantifying any increases using this, and again, using it too much can cause you to slow and finding yourself needing to accelerate again, wasting energy. There are some expert Prius drivers who never use this mode, and others who use it extensively on the highway. It's more that this mode will teach you to use the minimum amount of gas to stay at your desired speed. You'll feel as though you're already doing this, getting 50 mpg over a distance, but if you let up, you'll likely find you can maintain your speed getting 60-70 mpg.
EDIT on May 1, 2011: I've somewhat revised my opinions of SHM to hold it in a very positive light, since I got
wonderful mileage using it today on a 50-mile highway run, and that was far from flat ground. The trouble is, this post is for Beginning Prius tips, and you would need a
Scangauge to use the same technique I did, so it may not be practical for everyone.
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Technique #4 - Regenerative braking
What it is
Regenerative braking is a braking system that allows you to reuse some of the energy your car has stored when slowing down. Most cars use friction brakes all the time. In these systems, your brake pads come in contact with a metal disc, forcing it to slow down by all the friction created. The friction produces heat, and this energy in the form of heat is thrown away, never to be seen again. That is the kinetic, or movement-related, energy being wasted. Don't try feeling this on a regular car, since the brakes can heat up to dangerously high temperatures - like towards 1000°F. You could, though, with some caution, try feeling the wheel of a bike just after you've braked. That thing will get hot, and that's all that's left over from your wasted momentum!
In a regenerative braking scenario, the kinetic energy of the car, by way of the turning wheels, spins around the motor-cum-generator, producing electricity which is fed into your battery pack. It is not at all 100% efficient. You may only capture 30-some percent of the kinetic energy, but it's certainly better than nothing.
The Prius largely tries to use regenerative braking. The exceptions are when you brake hard/suddenly, in which case it will use the friction brakes in conjunction with regen, and also when you go below 7 mph, since hardly any energy is being produced down in that range anyway. It blends the use of regen and friction braking for when you need to brake more.
How to use it
Just hit the brake pedal! You can also just lift your foot off the gas. This much is obvious, the real question is
when to use it, and the answer is almost never.
For the most part, you want to avoid using braking at all, whether regen or friction. Any typical drive on even sparsely populated roads will reveal a sea of flashing red tail lights from the cars ahead of you, as they brake at every little speed variation of the car directly in front of them. Instead of braking with everyone for the Christmas light show, instead follow a safe distance behind the car in front of you. When this braking "noise" enters into the mix, largely ignore it, since they're about to accelerate again anyway. Your job is to conserve momentum.
There will always come points in your driving when you have to brake. I'm not saying to stop braking altogether (good luck with that!), but rather learn to eliminate the useless brake-for-a-split-second/accelerate-back-to-where-I-was-a-second-ago behavior that most cars demonstrate. Even with regen braking, this is an inherently inefficient way to drive. Try to conserve momentum.
To brake to enhance power regeneration leading up to stoplights or a stop sign, slowly depress the brake pedal so that you are slowing down gradually.
Braking blend between regen and friction, from the 2004 Prius New Features Manual
You will generate more electricity this way than if you drove straight up to a light and stopped relatively quickly, as most cars do. Notice in the chart above that when little brake use is called for on the y-axis, the Prius will use all regenerative braking even over a length of time. When you see the next light (or even a light or two past that one) turning yellow, get off the gas right away, and either use a glide or regen if you think you'll have to stop or slow significantly.
Mileage
There will not be an easily quantifiable or noticeable increase in fuel economy, but it is there - have faith! Even if you never use electric mode by itself, energy from the battery pack is regularly used to assist in acceleration from dead stops, etc., and contributes to a more efficient driving scenario. The Prius takes care of all that for you, for most drivers there's no need to even give that a thought as you drive.
There are limited instances where regenerative braking will be of significant assist to your mileage. There is one bridge I have to take three times a week that is a killer on mileage. To make things worse after a huge climb, you have to come to a complete stop(!) at the end of it to pay a toll. Even with EZPass they have bars down, and you can't drive straight through until you've paid and the bar lifts up. Luckily I've found that with the right amount of regen on the backside of the bridge, I can fully charge the battery. Since the Prius likes to have a medium charged battery, it will work to get rid of that full battery by using that energy as much as possible, leading almost to a plug-in car-like efficiency. I've calculated that from the stopped tollbooth, over the next three miles, which include a start from 5 mph, a small hill, and also another bridge to climb, that I get approximately 70-80 mpg. This is an immense improvement over a regular acceleration with limited battery assist.
A picture of me trotting along on a slight uphill at 44 mph after this bridge. Notice the lack of gas use...
Please note that if you are ever going down a long hill in the mountains and find that you're braking excessively or that your battery is fully green, you should shift into B mode. Once your battery is "full" like that (really 80% charged), you will be using your friction brakes exclusively. To avoid them getting too hot (or overheating the brake fluid), go into B. That is the only practical application of B mode, to throw off heat via engine braking. Regardless of whatever your dealer told you (mine said it would miraculously charge the battery to 100% in two minutes!), it is an engine braking mode only. You can still drive in B mode, you don't have to switch back and forth from drive to B just to accelerate and brake, respectively.
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Technique #5 - Electric vehicle mode or EV mode
What it is
EV mode is a way to use the hybrid battery pack to power the car solo at slower speeds without using any fuel. In the Prius, you have a gas engine and an electric engine. EV is pretty self-explanatory - it just uses the electric motor.
How to use it
EV mode can only be used in certain conditions, and the car must always be warmed up. You must be going under 42 mph, or else the gas engine will come on. To activate EV, make sure the gas engine is off while driving (you learned to do this in the
glide section), and then apply the gas pedal only slightly more than a glide, to get this now familiar screen:
The car is now going along in EV mode with no gas use. Ahh, the silence...
If you have trouble getting into EV mode, but you feel the car is properly warmed up and you're under 42 mph, stop pulling your hair out, even if your engine is running while you guzzle along at 10 mph. You're in stage 3 operation, and want to get to stage 4. More info on this can be found back in the "Preparation" section of the
glide tutorial.
Mileage (but with caveats and stern warnings!)
While it's fun to do, thinking that you're getting infinite mpg, EV mode must counterintuitively be
extremely limited in its use, otherwise you will get
worse fuel economy.
Why is that? you're likely asking about now...
The energy of the hybrid battery pack does not magically materialize. Although regen braking can provide some juice, it's not typically an abundant flow of energy. Most of the energy in your battery comes from gasoline ("What?!?"). Yes, it's true. Our beloved Prii convert gas into energy by way of the electric motor. That's why you see this most of the time with your foot on the pedal:
There are two sets of arrows from the gas engine (the engine icon at the top center, in this picture labeled "moteur"), one to the wheels (driving the car) and another to the battery (charging the battery). While this is a relatively efficient charging, some of the energy is simply lost in the conversion from gas, through combustion, to the electric generator, into the battery. If you use EV mode too much, you'll deplete the battery, not to an extent that's damaging to the vehicle, but just so that you'll be directing lots of gas into recharging, instead of driving the car.
So, what are the restrictions for EV use?
1. Push the pedal very lightly. The screen does not differentiate between intense EV use and light EV use - it only shows yellow arrows. There can be huge variations in use that you can't see, from 5 amps to 50 amps (and beyond!). Keep it low.
2. Use it in parking lots. No sudden moves, like humans in Jurassic Park.
3. Use it lightly in slow traffic and traffic jams. I've found that in 0-25 mph situations that it can be used nicely to extend glides, or even for temporary steady state driving. There's one part in my commute where I have to drive about 20 mph for about 3/4 of a mile. I switch between EV and gliding to get through it. The gas engine at those speeds is hugely wasteful, and would be kicking along at terrible mpgs. I can only justify this tradeoff by, again, being very light on the pedal.
Others have argued that more EV use is never a good idea, because of the conversion losses from gas to electricity I described above. The thing is, in practice, a strictly theoretical persective does not work.
An example of a given commute with limited EV use:
The same commute with more extensive, but careful EV use:
You get the idea.
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Th, th, th, that's all, folks
Hope this was helpful to some. Please leave comments if you have any questions.
