driving in B

The noise you describe is normal, as the others have explained.

Seeing you are from Pennsylvania, I can't imaging a hill long enough to warrant the use of B mode. B mode throws away energy by spinning the engine. Generally it is better to recapture that energy by using regenerative braking. Just press on the brake pedal and stay in D.

If you find that the battery is fully charged after the downhill, the next time you might consider using B. Otherwise normal braking was the correct choice.

Tom

 

If by the bottom of the hill the engine is going very loud you have topped out the battery so using B mode is the right thing to do. The computer will look after your engine so stay in B until you get to the bottom of the hill. Engine revs will never exceed 5,000RPM which isn't high by todays standards, the same capacity engine in a Yaris would redline at over 6,000RPM.

 

In western PA I haven't shifted into B. Generally I go as far as Breezewood and have not found it needed on the Turnpike. Going south from Ebensburg to Portage or on PA164 I'll fill the battery but don't brake down the mountains. The mountain going south on I-80(?) from State College is much steeper. B mode may be a better option as I do brake most of the way down.

 

On long hills in New Hampshire where I know that "B" is not enough to prevent the battery from reaching full charge, I turn on the headlights to "HI". This burns off some of the recharging and lets the car go further before the battery reaches full charge.

On really nasty hills (Mt Washington), I may also turn on the air conditioner to "HI" as well. This use of electrical energy helps prevent the mechanical brakes from working and subsequently overheating once the battery is full and the engine is revved to the wall.

Actually, the Prius can do pretty well on the Rockpile's 4,700 foot drop from the summit. A lot of them go up and down.

 

B mode delays the onset of friction braking in the event that engine braking alone can't provide enough braking. When you don't use B mode, the Prius will still resort to engine braking once the battery becomes charged, it just waits longer and isn't quite as aggressive about it.

You seldom *need* to use B mode unless you are driving in the mountains. Many people *like* to use B mode for ease of control and a perceived sense of better control, but that is a subjective choice.

I suspect in your case you don't need B mode. Once again, if you find that the battery consistently charges to the point that engine braking occurs automatically, then you can consider engaging B mode as you head down the hill. You can tell when engine braking kicks in because the engine will sound like it is racing, so if you get this when in D consider using B next time. Otherwise just use D which will maximize your mileage.

Tom

 

There is no such thing as "too fast for B mode." B mode is engine braking, but unlike downshifting a conventional car (which could over-rev the engine) the Prius's computer keeps everything under control.

Unfortunately, cruise control will not slow down the car, so it's useless when you are going downhill on a hill steep enough to require braking.

I agree with this.

Not absolutely the only one, but just about! Note that not only the Prius, but all cars get better mileage going slower (though the Prius's best mileage is at a slower speed than other cars). Most drivers are in such a hurry to get where they're going that they don't care how much gasoline they burn. Consider those big, square SUVs going 5 to 10 mph over the speed limit. They are burning gas like nobody's business. Most folks think the speed limit is the slowest permissible speed, rather than the fastest. It's that sort of attitude that has gotten us into the mess we are in now.

Good for you for driving a little under the limit!

 

Nope :_> "B" is used only to avoid riding the brakes. There is never any need for the driver to use "B" to manage the battery; the car takes care of battery management all by itself.