How to Efficiently Drive a Prius

Hi Tom,

This is an indepth topic with lots of posts around.

The main thing to start off learning is how the accellerator peddle works. After you accellerate, if you pull back only as far as you are used to in other cars, the Prius will configure the transmission for rapid changes. This means keeping the engine running, and at a higher RPM than neccassary to move the car along at a constant speed. Although the car will move along at a constant speed. To get the car into more efficient configuration, one needs to pull somewhat farther back on the peddle. At some point the car will start to slow down. Over time you will learn how much you can lift and maintain speed. If you exceed 40 mph, the engine will jump back on.

The engine has its best efficiency about 2000 RPM. When you accellerate form a stop, this is just shy of where the battery will be called upon to provide extra accelleration power. So, initially you will see the yellow arrow on the MFD, then pull back a little until you get a green arrow or no arrows to/from the battery icon. You can increase peddle staying on green arrow as you accellerate. Some people say not to get the loop mode going for the extreme best mileage. But I find that is not practical in traffic. I shoot for either no arrows or green arrows, and avoid accellerations that uses battery. If it starts to loop power between the motors and the engine, so be it. The accleleration doing this way slower than many drivers , and way faster than many other drivers. Kinda in the middle. As the Prius does not have "fuel enrichment" it can accellerate pretty briskly without being too inefficient, unlike standard cars.

The gears in the Prius do not change. The engine and motors are always rigidly connected to the gears even when the car is stopped.

The HSD drive on the Prius does change modes. It has an accellerate mode, a glide mode which is kinda like coasting, but its envoked just by lifting off on the peddle just the right amount and way. It has an EV mode - where the car is rolling under electric drive only at slower speeds. it has a slow-speed highway mode which gives very good mileage and only uses the engine (people call this SHM - super highway mode), and it has a higher speed highway mode (typically up above 62 mph). It also has a downhill electric highway mode, where the battery pushes the car along, the engine is still turning, but there is no gasoline being injected into it.

The gliding mode can be invoked in a warmed up Prius at 40 mph or slower. The engine will turn off and the car will glide along. With a small peddle depression you can bring on the EV mode, and here in Chicagoland this is handy for cresting a small hill in the road and then gliding down the backside. Other cars do not even know you are doing this, as you just maintain the same speed.

Its not good to use the electric mode for accelleating from a stop. The car does not have sufficiently robust electrical system for that to be efficient.

 

The transmission as such doesn't shift, it's a smooth continuum
of effective ratio change all done by regulating torques and
speeds on electric motors. No mechanical shifting happens at all.
.
If you're a technical sort, you might be intrigued by some
training slides I worked up a while ago [with pix and diagrams
snagged from Toyota and some of our own tear-downs] which might
help, and at a minimum you should read Graham Davies' pages
about running operation as well as john1701a's seminal info
about it.
.
"Optimal" acceleration ranges are fairly generous, as long as you've
got the engine working reasonably hard [high torque == efficient]
which generally happens over a wide RPM range and it's just a
question of how much instantaneous power you want to send to the
wheels. Gentle, but not totally down in grandma territory, yields
good results.
.
_H*

 

As a newb to the Prius I would say - Observe what is happening depending on where your foot is on the pedal. It's very sensitive, and what it does is dependent on what state the car is in. (it goes through different states as the engine warms up). It's very easy to learn how to get the car to glide and to 'golf cart' at low speeds.

 

52mpg sounds about right for 35-40mph rural driving. I did about 40 miles of that today and got around 57mpg.

I'm still learning how best to deal with stop and go, stop and go, etc...it is cool when sitting next to a car at a stop light and the car just "shuts off"... I'm always thinking about the car idling next to mine..."SUCKAH!!!" ha ha ha...

 

I would be very happy averaging 52mpg. I've gotten mine to 46 and change, with only 400 miles on the clock, so I'm happy.

 

It is bad to top-off. It increases hydrocarbon pollution (by saturating the vapor recovery canister with liquid) and can actually damage the fuel tank and its computer.

The pips have variable meaning from car-to-car and from fillup-to-fillup. The *only* rule is: when the last one starts to flash you are about to run out of gas, no matter how much gas you put in last time or how far you've driven. There's no way to be certain how far you can drive from that point, therefore it is prudent to fill-up before that point.

Do not drive after running out of gas unless absolutely necessary. The battery will not take you more than a mile in any case, and draining the battery below two purple bars on the display reduces its life.

Fuel economy short-path zen: Brakes, Battery, And "B" Are Bad; therefore
- Accelerate briskly; the engine is most efficient near full load.
- Gliding (no arrows on the "Energy" display) is better than coasting
- Coasting (arrow into the battery on the "Energy" display) is better than braking
- Braking is better than stopping
- Stopping is better than running into something
Applying these principles in actual driving without inducing road rage in others is left as an exercise for the driver. Ideally one would accelerate to some speed and then glide all the way to the next stop, which is clearly infeasible in most real situations. "B" is to be used only on long downgrades, to avoid riding the brakes.

Check tire pressures also at least monthly. Many of us use 42/40 PSI front/rear to improve fuel economy, at the cost of a harsher ride.

Keep in mind that the battery system gets its cooling air from the cabin. If the battery system gets hot its efficiency, and thus your fuel economy, will drop. Rule of thumb: if you are uncomfortably warm then so is the battery, and you should turn ON your A/C. (Yes, this is one more way in which Prius is not like conventional cars.)

If you do not have covered parking during the day consider a custom Sunshade for the front window, and then park facing south or southwest. Many Toyota dealers have these; I'd recommend the folding style and not the roll-up.

 

And lastly the Climate control (especially the heater) can kill gas mileage, especially when at higher fan speeds.

 

The purpose of the bladder is to reduce evaporative emissions by decreasing the amount of air space in the fuel tank.

 

That pretty much covers it. You can accelerate with the traffic flow & still get good mileage. I use moderate to brisk acceleration, then back off & let the mpg max out while maintaining or slightly decreasing in mph depending upon the road situation. I think it is helpful to set your screen where you are seeing the mpg you are getting right now & you'll quickly learn what increases/decreases your mileage.

On hills if I can cheat a little & pick up a little momentum/speed going down one, I then feather off a bit on the next climb & seems to work pretty well. I think it is better than trying to hold a constant speed, which means I don't always use my cruise in the hills.

 

Learn to accelerate evenly and smoothly. Since you have a constant velocity transmission you don't have to worry about what gear you are in. When you are up to speed, pretend you have an egg between your foot and the pedal and focus your sights about 1/4 mile ahead of you when you are driving and coast as much as you can (engine off). Absolutely do not tailgate, this will force you to brake and gas and brake and gas. City driving I get: Summer 60 mpg and winter (Chicago) 45 mpg. Hope this helps.
go

 

It is better to coast than to use B because you charge your battery while coasting. To glide the engine must be completely warmed up, and you have to be going slower than 42 mph. It is easier to glide on flat and downhill sections of the road.

 

Sorry, yes you have to slightly press the accelerator to glide. If you let the accelerator all the way up you are coasting.

 

Don't use "B" on icy roads. In "B" you are always getting some regenerative and/or "jake" braking, and there are times when you don't want to be braking on an icy road.

Don't use "B" for slowing down in normal traffic because it it wastes energy unnecessarily. That use of "B" is perfectly safe, but it will reduce fuel economy. Learning to glide is better (below).

You can indeed glide going uphill, and of course the car will slow down while doing so. Getting into glide is a matter of applying just the right amount of pressure on the gas pedal in a given situation. Glance at the display to see whether it is happening. After some practice it is possible to sense when you're doing it from the sound of the drive system and acceleration.

Most importantly, don't stress about any of this. If you're not enjoying it it's not worth it.

 

FYI: When using "B" you DO charge the battery; & that is a fact.