Regenerative brakes versus friction (regular) brakes

Wow! I've seen a lot of theories about car care come and go in my time and I have only one suggestion to make. Do as TOYOTA says. Toyota says on the '04 Prii, change the oil every 5000 miles when you're driving under NORMAL conditions. (No taxi work. No Sahara desert). I truly believeTOYOTA knows more about the car it created than anybody else. Concerns about sulphur content or additive diminishment may be mis -applied in our case with the Prius. Even so called experts are mistaken now and then. For example an expert who recommends changing oil at a shorter interval than the one recommended by Toyota for the Prius may be talking about all the other cars that are now somewhat old fashioned. I remember when the Prius first appeared in this country how a so-called expert couldn't grasp the concept that the Prius mileage in town was greater than its highway mileage. He thought it was an error so he transposed the figures. So much for experts and bonifide field tests. Higher octane fuel? Toyota says, in fact it insists that only 87 octane fuel be used. The variable valve timing in the Atkinson engine as employed by Toyota REQUIRES 87 octane. Not higher. Habitual use of higher octane fuels can actually damage the engine in the Prius. And one more important thing to remember if I may be so bold to admonish. Never, never under any circumstances drive the Prius on its battery to the point it becomes exhausted. The Prius high voltage battery is made up of many lower voltage cells and not all cells, even when brand new, are created equal. It is possible the some of the cells may deplete sooner than others and become "reverse polarized." When that happens, the cell is never any good again. DON'T DO IT. Let's all do as TOYOTA recommends and when somebody buys our used Prii, they'll get a bargain. Whatshisname. :wink:

 

Can you cite a source for that? Page 202 of the 2004 owner's manual says 87 octane *or higher*. There's nothing about not using higher octane gas.

I agree completely about the wisdom of following Toyota's recommendations. "Use only 87 octane gas" does not appear to be one of these.

 

I use the 87 octane gas. I only do because the manual says that. Otherwise I would be putting in Premium!!!

Brian

 

Where?

thanks,
Richard

 

Since the regen braking converts motion to current it needs there to be motion, ie there is less effect as you slow down. The computers apply the mechanical brakes for the last 5 to 8 mph of any stop regardless of how gentle. OTOH this leads to very little wear of and by itself. OTOOH if you go to the brake pedal rapidly from the the gas there is a computer that reads this as a panic situation and applies the friction brakes at any speed as well as the regen. Peace, Ammiel

 

Richard! Thank you for your interest in my remarks concerning the Atkinson engine. I have extracted from several sources the admonition concerning the use of higher octane fuel in the engine, but I am unable to cite them at the moment. I gathered from my readings and stated opinions outside the Prius manual that there was a concern about eventual "valve burn" developing from remaining unused energy released during valve openings. I can understand where Toyota might permit the use of higher octane fuels paticularly in higher altitudes since the Prius is sold all over the world. Never-the-less, based on what appears to me to be a concensus among experts familiar with the engine, the continual use of higher octane fuels is of no benefit under normal operating situations and may be harmful. I assure you, the next time I encounter information concerning the Atkinson engine and its fueling I will post it here hoping you find it. However, I must persist in my suggestion to the group to avoid the use of higher octane fuels, particualrly those boosted by additives and do as Toyota specified by number. That number being 87. Whatshisname. 8)

 

This topic drifted.

So again, I will offer my foolproof method to determine when the conventional friction brakes kick in.

Leave your car out in the rain.

Afterwards?

Listen.

 

I'd just like to make some comments regarding some of what I've read here:

1) With today's oils, 3,000 mile oil changes are simply silly and just add to environmental polution. When Audi switched from 5,000 to 10,000 mile oil changes I did significant research and found that present day oils, along with their additives, hold up very well beyond 5,000 miles and don't show deteriation deserving of concern (still, to be on the safe side I brought my own full synthetic). I should also mention that Audi's 1.8t turbo engine puts a lot more strain on oils than this narrow RPM band wonder that we're using.

2) The term, "premium" shouldn't be allowed. Premium means, "of superior quality or value". In reality, for cars rated at 87 octane (86 octane >2,500 feet, 85 octane >5,000 feet), premium is simply a waste of money and provides no, "superior quality or value" whatsoever.

3) Most European countries use RON octane as their reference. The U.S. and Canada use (MON+RON)/2. The difference is 4 to 5 octane points for the same octane effect with the European number reading higher.

 

My manual reads "select unleaded gasoline with an octane rating of 87 (research octane number 91) or higher. yours states something different? Toyota recommends the use of cleaner burning gas including reformulated gas that contains oxygenates such as ethanol or MTBE. Thats what it reads anyway

 

It does in one respect: generally lower sulfur content than 87 octane. This means longer life for the catalytic convertor and less pollution.

I agree, it does not provide any (other) operational or performance benefit; if a modern engine pings using 87 octane at low altitude it almost certainly needs service, not higher-octane gas.

 

If Atkinson cycle means nothing to you (as it did for me) at http://www.keveney.com/Atkinson.html there is a simple illustration of the device. Or try Wilkipedia (http://en.wikipedia.org/wiki/Atkinson_Cycle)

 

More to the point is whether Toyota understands the Atkinson cycle. I'll bet that they do (but arguably it would be more accurate to call it a Miller cycle engine, since it uses variable valve timing and does not use a variable-length stroke). Anyway, the Toyota site is useful:

http://www.toyota.co.jp/en/tech/environmen...hs2/engine.html

Graham's site has additional discussion:

http://home.earthlink.net/~graham1/MyToyot...lCombustion.htm


The Prius' owner's manual states explicitly that octane greater than 87 is acceptable. If it were harmful, don'tcha think that the owner's manual would say so?

If someone can provide a technical reference saying otherwise (preferably one with some specific explanation of *why* higher octane gas would be harmful to *this engine*, not just a passing general mention of detonation and burnt valves), I'd love to read it.