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Discussion Starter #1
Yesterday it was warm and I ran the A/C as I was driving home from about 40 miles away. I had been driving on the interstate for 25 or 30 miles and then had to go through some congestion on a secondary road.

I was creeping along with ICE off (according to the Coastal run light) when I noticed that I could still *hear* the ICE running. I switched to the energy display and saw that indeed I was running stealth, but I could still hear it. After a bit it stopped. When I accelerated, the run light came on, the ICE sound started and things worked as expected. This happened several times, including when I was at a complete stop.

So my theory is that the battery was sufficiently charged the the various ECUs together decided the run the A/C compressor by using MG1 to turn the ICE, but without giving the ICE gas or spark. With no gas, the fuel pump (and thus the Coastal run light) was off, but since MG1 was turning the ICE in order to crank the A/C compressor, I could still hear it.

What do you think?

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Discussion Starter #2
The ICE runs the A/C. Just because the montior shows no power from the ICE doesn't mean it's not running
 
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Discussion Starter #3
Your only evidence is that you could "hear" the ICE
"running" - and while you were creeping no less. At low
RPMs, the ICE is very quite, even when under power. Being
driven by a motor with no gas, it's likely quiter still.

Any chance you heard something else, and mistook it
for the ICE spinning?

I for one would want more evidence than sound - a tach
for instance, before I'm ready to believe this mode of
operation.

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Discussion Starter #4
Burns,

I have a tach and have at least twice suspected the same event. I will check more carefully and report back.

Interestingly, I believe that I also hear the A/C condensor fan(s) running when this happens. I have always reached up pushed the A/C button off without considering what you say here. I will test and post.

Wow, if this is true, Toyta really should consider an electrically driven scroll compressor for A/C!

Wayne
 
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Discussion Starter #5
The main evidence of the ICE not running is the Coastal Tech ICE run monitor, not the multidisplay. The Coastal ICE monitor is lighted when the fuel pump is running, so what I'm saying is that I hear ICE-like sounds when the fuel pump was turned off.

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Discussion Starter #6
Harry, I agree that I would like more evidence that the ICE is turning. As I said above, the evidence I have for the ICE not actually consuming gas is that the fuel pump was turned off. I have only audio to suggest that the ICE might be turning.

I've had Lux for 7 months and I'm pretty familiar with the sounds of stealth. I could not swear that the ICE was turning, but I've never heard another sound like that. I also compared it with the sound when the ICE actually did come on (as evidenced by the fuel pump light). It was very similar.

I sure wish I had thought to turn the A/C off to see if anything changed.

Anyway, this is a hypothesis. Let's try to find confirmation. If anyone else notices this, if you have a tach please try to take a reading (although if the tach works on the spark or fuel injectors, it will not show anything interesting). Also try turning off the A/C (or notice if you hear this with the A/C turned off). Can we think of any other experiments?

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Discussion Starter #7
Sorry for yet another post, but after re-reading Wayne's post, it occurs to me that it is possible that I heard the radiator/condensor fan. (Naturally the evaporator fan in the cabin was running). If so, it sure sounds different from other radiator fans I have heard. In any case, I'm not sure I have ever noticed the radiator/condensor fan separately from the ICE. I will experiment to see if I can find a way distinguish the two sounds.

Does anyone know whether the radiator fan ever runs in stealth mode (ignoring A/C for the moment)?

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Discussion Starter #8
----Original Message-----
> From: Burns Fisher

> Does anyone know whether the radiator fan ever runs in stealth mode
> (ignoring A/C for the moment)?

The ICE has two water pumps. One is mechanical and driven by the same belt that drives the A/C scroll compressor. The other is electric and can circulate cooling water through the ICE when it is in stealth. It seems perfectly reasonable that the radiator cooling fan would run while the ICE electric water pump is running. Maybe it sounded strange because when you were in stealth you heard both the ICE electric water pump and the electric radiator fan at the same time?

Ed
 
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Discussion Starter #9
I have not been able to make this happen again. I have been poking through the New Car Features manual and discovered an interesting thing or two.

First, the electric cooling pump mentioned above is apparently only to keep the heat working smoothly when the ice stops rather than to cool the engine. However, there is yet a third cooling pump which I assume is electrical; this the the pump for the MG1/MG2 coolant loop. I suppose it is possible that I heard this. However, if I believed this, I would have to believe that it is on seldom, because, as I say, this sound was very ICE-like and quite easy to notice.

Anyway, I'm keeping my ears open.

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Discussion Starter #10
The MG's coolant pump runs very quietly. It has a high but quiet pitch which sounds almost like a capacitor that is loading up.

I too have been trying to get my Prius to do what you describe and have not been successful. I really think that I did catch this at least once, if not twice and gave it little thought until you started this thread.

I had the A/C on. My tach was showing no ICE and I was doing about 20 mph in Stealth in my neighborhood where I almost always do Stealth. I heard the ICE and condensor/radiator fans, saw no tach and without thinking reached up and turned off my A/C button and about 1 second later the ICE and fan sounds stopped. The whole time I never came out of Stealt according to my tach.

I'll keep trying.

Wayne
Pittsburg, TX
 

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Burns Fisher said:
<snip>
I was creeping along with ICE off (according to the Coastal run light)
</snip>
Folks - the Coastel ICE light monitors power to the fuel pump. If it says the ICE is off - it's either OFF or running on something other than gasoline...
 

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I believe that this Mode absolutely does exist, I had noticed it a few times myself prior to reading this article. Also, another similar "no gas" A/C mode happens sometimes whilst going down long hill. The ICE can be heard and felt to start rotating as though in B mode as the A/C fans kick in whilst going downhill below 42 MPH, yet MPG is still showing 100MPG so no fuel is being used. Hitting the a/c button to turn it off causes the ICE to stop rotating and you can feel the ICE braking effect "let go"

All this is subtle stuff which only long experienced and observant Prius drivers can pick up on, but I am sure it is valid, and logical if you think about it. I mean why burn fuel to run the a/c if going down a long steep hill, much better to use the cars kinetic energy to drive the a/c!

Peter Rawlinson
 
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