loud fan noise after long downhill using B

[Paul R. Haller]

I drive to work each weekday and with my new 06 prius I hear, after the battery has all green bars charged, and on a long downgrade, a loud fan like noise comming from the engine compartment but I'm not sure it's true location. It does change tone with engine RPM but without a tach it's impossible to say. If this were a conventional car and in first going down a hill I would just say its the engine racing but it only happens when the green bars have all appeared in the battery icon and this car as far as I can tell doesn't run the ICE at all going down a grade. It stops as soon as I shift out of B and into forward. It's like the CPU runs a motor to spill off excess charge.

Anyone have any Ideas? Thanks in advance.
-Paul R. Haller-

[eagle33199]

There are various methods in which the Prius bleeds off excess energy when it needs to, including spinning up various items in the engine compartments. Otherse have posted that, when they had full green bars, their ICE cycled on and off while sitting at a stop light (no gas was burned, spinning it up is just a good way to bleed off extra energy).

As for the fan, are you sure it's not coming from the back? It's possible that, after a fairly quick charging cycle like you described, the battery compartment heated up (charging will do that to batteries), and it had to bump the fan speed up to cool it down.

[M. Oiseau]

Might it be the freewheeling ICE? Do you remember your speed when disengaging B-mode?

[efusco]

It is the ICE spinning, it's draining the battery to prevent overcharging.

[kevinwhite]

<div class='quotetop'>QUOTE(Paul R. Haller @ Aug 15 2006, 11:10 AM) [snapback]303609[/snapback]</div>

I drive to work each weekday and with my new 06 prius I hear, after the battery has all green bars charged, and on a long downgrade, a loud fan like noise comming from the engine compartment but I'm not sure it's true location. It does change tone with engine RPM but without a tach it's impossible to say. If this were a conventional car and in first going down a hill I would just say its the engine racing but it only happens when the green bars have all appeared in the battery icon and this car as far as I can tell doesn't run the ICE at all going down a grade. It stops as soon as I shift out of B and into forward. It's like the CPU runs a motor to spill off excess charge.

Anyone have any Ideas? Thanks in advance.
-Paul R. Haller-
[/b]

Paul,

In B mode the ICE is spun (without using gas) to brake the car. It is similar to the Jake brake used in trucks, or putting a conventional car into low gear to descend a hill.

kevin

[cagemo]

<div class='quotetop'>QUOTE(Paul R. Haller @ Aug 15 2006, 11:10 AM) [snapback]303609[/snapback]</div>

a loud fan like noise comming from the engine compartment but I'm not sure it's true location. It does change tone with engine RPM but without a tach it's impossible to say.
[/b]

But given how you describe it, I agree with Eagle - it may be the battery fan running. It's next to the back seat, on the passenger side. Listen closely or even stop the car. That fan can be very loud, but hard to pinpoint and the sound blends with the engine noise.

Where do you live? If it's hot outside (and inside your car), that can heat up the battery and kick the fan on high too.

[Paul R. Haller]

As I said, its not obvious where the noise comes from but tomorow driving to work I'll try and pinpoint where it's comming from. My guess is that the CPU is spilling off excess charge somehow but it could be the fan in the back, I never considered that. I'll check furthur tomorrow. Thanks guys, I don't think anything is wrong but I thought I would ask. I live in the SF bay area and more specifically I drive from my home in Walnut Creek to Cal Berkeley over the Berkeley hills on Fishranch road. Round trip about 32 miles. Today the average temp in the peoples republic was about 75. I think there are more hybrids in Berkeley then anywhere else in the US. They are taking over!
-Paul R. Haller-

[dreichla]

<div class='quotetop'>QUOTE(efusco @ Aug 15 2006, 02:23 PM) [snapback]303618[/snapback]</div>

It is the ICE spinning, it's draining the battery to prevent overcharging.
[/b]

I agree - this happens once in a while during a long downhill stretch of road I usually take. I then put the car back in drive and the engine racing stops immediately. It doesn't seem right though.