Engine On 'n Off

[Stev0]

Today I was showing off my Prius to an engineer who never rode in one. I was showing him the various displays, and he asked a question I should know the answer to but don't.

I was bragging how it saves gas by turning the engine off whenever I take my foot off the gas or come to a complete stop. He said that most wear-and-tear on engines happens when they start up, so how does it deal with that?

Well, how does it?

[JimN]

<div class='quotetop'>QUOTE(Stev0 @ Jun 7 2007, 09:47 PM) [snapback]457768[/snapback]</div>

Today I was showing off my Prius to an engineer who never rode in one. I was showing him the various displays, and he asked a question I should know the answer to but don't.

I was bragging how it saves gas by turning the engine off whenever I take my foot off the gas or come to a complete stop. He said that most wear-and-tear on engines happens when they start up, so how does it deal with that?

Well, how does it?
[/b]

Part of the answer is that the engine is turning (causing lubrication) but the valves are open (not causing combustion). Now the technically inclined can supply a more complete and accurate answer.

[lowspeed]

<div class='quotetop'>QUOTE(Stev0 @ Jun 7 2007, 10:47 PM) [snapback]457768[/snapback]</div>

Today I was showing off my Prius to an engineer who never rode in one. I was showing him the various displays, and he asked a question I should know the answer to but don't.

I was bragging how it saves gas by turning the engine off whenever I take my foot off the gas or come to a complete stop. He said that most wear-and-tear on engines happens when they start up, so how does it deal with that?

Well, how does it?
[/b]

Why would you know the answer for that ? it's really not common knowledge.

There's plenty of threads on how the engine (ICE) works.

In short and quoted from wiki "The frequent starting and stopping of the engine does not cause additional wear and tear or emission problems because the drive motors have enough power to quickly spin the engine to optimal rpm (around 1,000) before the engine fires up. This avoids the wear that would occur if the engine were to run (with fuel and spark) at very low rpm."




I

[jimmyrose]

In addition to the previously stated, I'm under the impression that the wear and tear on engines is most significant on cold start ups.

[efusco]

The advantage of the MG1 spinning up the ICE is that oil pressure is built before ignition, thus the wear of a cold start of an unlubricated system is averted.

[YoDaddyAlex]

i heard starting an engine takes as much gas as it would be running for a minute. is it not true, or just different with a prius?

[ken1784]

<div class='quotetop'>QUOTE(YodaddyAlex @ Jun 9 2007, 09:42 AM) [snapback]458383[/snapback]</div>

i heard starting an engine takes as much gas as it would be running for a minute. is it not true, or just different with a prius?
[/b]

We see about 1 cc (0.000264 gallon) consumption when Prius engine starts.
Driving 30 mph at 50 mpg, Prius consumes 37.85 cc (0.01 gallon) per minutes.

Ken@Japan

[efusco]

To add to Ken's answer, there's about 200amps used to spin the ICE before ignition...so I'm told...

[ekpolk]

<div class='quotetop'>QUOTE(efusco @ Jun 8 2007, 10:09 PM) [snapback]458476[/snapback]</div>

To add to Ken's answer, there's about 200amps used to spin the ICE before ignition...so I'm told...
[/b]

And to think, our now-defunct electric chair never pumped more than about eight amps through the miscreants it had to dispatch. I suppose there's a good reason why those thick cables are colored bright orange... :P

Seriously though, yes, the way the MGs spin up the engine before it lights off is akin to the function of the pre-oilers you can install on a conventional car to reduce wear on a cold start. Amsoil sells a kit for about $250 IIRC. You'd never need such a contraption for a Prius; I doubt its bearings ever see a load without solid oil pressure already there to keep things separated.

[TonyPSchaefer]

And to think, when I was asked that very same question, my answer was more along the lines of, "it doesn't work the same way as other cars so the engine doesn't have that wear of constantly starting and stopping."

Now I feel a little over-simplistic.