Greetings! I am turning to the group because the dealer has no clue about this. We live at the top of a 12-mile (20 km) hill and with a couple of very short exceptions (a slight climb over 200 yds and a couple of 200 yd level sections) the entire 12 miles is downhill. The ICE in our new Prius with 1850 miles on the clock runs almost the entire way down the hill--20 out of the 25 minutes it takes to get down. We are not using the heat or AC, the radio is off, no rear window defroster and the outside temp is 40-50 F. I cannot find any explanation for why this should be in the manual and the dealer is useless. Can anyone explain why it should do so? Is there something wrong whih needs to be fixed (by another dealer...)? Thanks for your thoughts!<br>Alan

Does the power display show an arrow coming from<br>the ICE, or is it just idling?&lt;br&gt;&lt;br&gt;Some amount of<br>ICE is normal during the start of a drive, to get the<br>catalytic converter nice and warm and effective. It should<br>be just idling, not driving the wheels.&lt;br&gt;&lt;br&gt;For<br>me that initial idling usually stops after about 10<br>minutes, rather than the 20 you're seeing.&lt;br&gt;&lt;br&gt;Oh,<br>wait. If you live at the top of a 12-mile hill, you had<br>to climb the hill to get home. The computer may have<br>used electic assist to get you uphill. That would have<br>left the battery at the low end of its charge range.<br>The ICE might be running to recharge the battery.

A puzzler!<br><br>12 miles=25 minutes, around 30 MPH avg. Are you in "B" range for steep descents?<br><br>What's your 1800 mile MPG?<br><br>Jeff

Thanks for the response! The overall mpg fuel use for 1800 miles is 41 mpg--this includes highway driving at 65-75 mph (about 1000 miles of steep inclines and hilly terrain), up that 12 mile hill and down, driving around town, several 70 mile round trip treks a couple of times a week etc. "B" range is used only rarely for the descent and it has been suggested that the engine may be running to keep sufficient vacuum in the power brake system, though I brake pretty carefully and actually pretty rarely but still accumulate 1.5 to 4 "stars" per 5" period. Yet the ICE keeps running the whole way down the hill, even though the engine isn't cold, and it isn't cold outside. I have not reset the mileage and fuel use computer to calculate actual fuel consumption for the up and/or down segments, but the green bars for the 25" indicate "maximum" consumption for 15" (about 23 mpg) and about 30 mpg for the other 10 minutes. After getting to the bottom of the hill the engine continues to run for several minutes/2 stoplights, then performs as expected, shutting down at the light or stop. The "consumption" display occassionally reads "maximum" consumption (green bar all the way up), even when stopped with the engine off, and occassionally reads "0" consumption (no green bar at all) with the engine off when stopped at a light. No pattern to that, however. This whole thing is frustrating to say the least. Any and all suggestions appreciated!<br><br>Alan

On occassion the power display shows the arrow from the ICE, but only when on a level stretch of road or a slight incline and I know the engine should be operating the drive wheels. The rest of the time it does not show an arrow, but the eingine continues to run (I can hear it) and the "Consumption" display shows the fuel use. The initial idle time to get the blue thermometer to go away is short--5 minutes max--and the battery is never more than between 1/3 and 1/2 empty at the end of the drive up, and fully charged (right up to the top of battery box with no letters showing and right up to the battery posts) by 1/4 to 1/3 down the hill, so the engine isn't running to charge the battery, or shouldn't be, because the battery has been recharged by rolling or RG braking. Again the dealer has no idea, blowing me off, basically.

The engine will always run the first 5 minutes (at least) after a cold start. This allows the catalytic converter to come up to operating temperature (remember, the primary design goal is low emissions...). When it is cold outside, the engine will run longer on initial start, and also more frequently after it warms up (the CC will cool down faster in cold weather, so the ICE has to start more often to keep it hot).<br><br>Current MPG display should very quickly go to 0 when you stop, although there is a 2-3 second lag between any action and the display update. The factors that determine whether the engine will actually turn off when you stop are CC temperature, battery charge state, and A/C setting (MAX and the defrost position will both force the ICE to continuously run).<br><br>Hope this helps.<br><br>p

According to my research the engine has 2 modes<br>of running - one in what i term 'spinner mode'<br>around 200RPM which is preparatory for full mode.<br>There is a mechanical term that is more accurate<br>but i would have to pull up one of my research papers on it. Essentially the motor plays at 200RPM until it is needed, if not then 0RPM otherwise it will go up to full throttle in the range needed, 300RPM - 5000RPM? depending on conditions, hope i've helped a bit in lay mans<br>terms - i am not a mechanic

I'm not sure where akkadian2010 did the research, but the top speed of the engine is 4500 RPM according to the Prius New Car Features book and several other sources. Also, the low end speed is probably between 800 and 1000 RPM. There has been speculation that it may have a "fuel cut" mode where it spins at around 800-1000 RPM without fuel due to generation forces from the generator (official name Motor/Generator 1 or MG1). And of course, there's our favorite mode, lovingly refered to as "stealth mode" where the engine doesn't spin at all (or use any fuel). But "stealth mode" only works at speeds less than around 40 MPH.<br><br>Robert Snyder<br>NJ-PIKACHU

Pika,<br><br>Baby here--fuel cut or fuel "starvation" &gt; 42MPH<br>mode?<br><br>We last discussed a month ago?<br><br>Has it been decided?<br><br>Still waiting for Laptop pwr supply so's I can try an' get OBD-2 to not say "busy". That'll say for sure.<br><br>Jeff

Robert,<br><br>Glad to see you are still active in the club. It saves me responding to many of the repeat questions. You are correct 4500 rpm max. Idle 1000. If speed less than 42 mph, coast, braking or light throttle; no spark , no fuel, engine stopped. If speed greater than 42 mph, coast or braking; no spark, no fuel, engine spinning to avoid overspeed of MG1. <br><br>Common auto industry techno-babble, fuel cut = no injection for combustion. Similarly spark cut = no ignition spark. Note: both terms and related phenomena are sometimes used in conventional vehicles in much more limited ways for different reasons (engine speed limitation and emissions control come to mind).<br><br>Dave

Hi Dave,<br>Thanks so much for the idle speed and fuel cut/spark cut info. I'm pretty sure I heard the original rumor 3rd hand from people (Bill & ?) who met you at an SAE meeting in NJ last year. So now I can just state it as fact. Cool. This car has so many neat tricks.<br><br>I made a big drawing of the transmission nomograph along with a description in a file called Nomograph.pdf in <br><br><a href=http://groups.yahoo.com/group/toyota-prius/files/%20Technical/ target=new>http://groups.yahoo.com/group/toyota-prius/files/%20Technical/</a><br\ ><br>You might find it entertaining some time when you have extra free time. And I'd love feedback on any errors.<br><br>Note to Jeff/Baby: I've got the cord and the laptop, but haven't found time to download the program yet. I've been pretty busy the last couple weeks.<br><br>Robert Snyder<br>NJ-PIKACHU (with allergy season in full force, this sound takes on new meaning).