Premium fuel in the GX470 necessary?

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Old 05 Dec 2003, 12:20 am   #11 (permalink)
Tsheer
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Default Re: Premium fuel in the GX470 necessary?


"sf/gf" <sf90006@kart.com> wrote in message
news:ObVzb.29152$sb4.17536@newsread2.news.pas.eart hlink.net...
>
> <wideglide01diespammers@cox.net> wrote in message
> news:rflvsvsul9klcrf91ohfb8tra90a2dnv3m@4ax.com...
>
> >
> >
> > You *can* damage your engine by going with too *high* of an octane
> > fuel for an engine that's not designed for it. Higher octane is to

>
> >
> >
> > ************************************************** ********************
> >

>
> Please explain how using too high of an octane fuel can damage an engine.
> Although it may not make sense from an economic viewpoint, the only
> difference between low octane and higher octane is that higher octane

burns
> slower (which is why it pings and knocks less). Some say higher octane

also
> has higher detergent levels, but I have never been able to verify this.
>

Gas doesn't burn "slower" or "faster". The octane rating is relative to
the temperature
at which the gas burns. Higher octane gas combusts at a higher temperature
than lower
octane gas. Compression heats the fuel/air mixture, and if the octane level
is too low
for the engine, the fuel/air will combust from the compression heat before
the spark plug
ignites it. That causes knocking.


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Old 05 Dec 2003, 01:05 am   #12 (permalink)
markjen
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Default Re: Premium fuel in the GX470 necessary?

> If you don't
> have a high compression engine or if you're not getting any knocking,
> you're not going to lose losing power and your not going to hurt your
> engine.


Well, this is a chicken/egg argument. No, you're not going to be able to
detect knocking on regular, but that's because the engine has detected it
long before you could, and has reduced engine preformance to elminate it.

So "not getting any knocking" tells you basically nothing about what your
engine is doing or what octane appetite it has.

- Mark


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Old 05 Dec 2003, 01:06 am   #13 (permalink)
markjen
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Default Re: Premium fuel in the GX470 necessary?

> Please explain how using too high of an octane fuel can damage an engine.

You're right, it can't. This is an old wive's tale. Using a high-octane
fuel in an engine designed for lower-octane does nothing except waste money.

- Mark


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Old 05 Dec 2003, 01:08 am   #14 (permalink)
markjen
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Default Re: Premium fuel in the GX470 necessary?

> You do not need to use premium. The engine down-tunes itself for lower
> octance gas, with no ill-effects.


Except a loss in performance. You may not detect it, but the dyno doesn't
lie - you run most premium engines on regular and peak horsepower drops 10%
or so.

- Mark


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Old 05 Dec 2003, 01:10 am   #15 (permalink)
markjen
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Default Re: Premium fuel in the GX470 necessary?

> from: "The Low-Down on High Octane Gasoline"
>
> http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm


This document says nothing about modern engines with knock-sensors. It is
completely out of date.

- Mark


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Old 05 Dec 2003, 08:29 am   #16 (permalink)
Dan J.S.
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Default Re: Premium fuel in the GX470 necessary?


"markjen" <mark.jennings4@comcast.net> wrote in message
news9Wzb.433293$Fm2.434640@attbi_s04...
> > You do not need to use premium. The engine down-tunes itself for lower
> > octance gas, with no ill-effects.

>
> Except a loss in performance. You may not detect it, but the dyno doesn't
> lie - you run most premium engines on regular and peak horsepower drops

10%
> or so.
>
> - Mark


From some of the reports that I saw, it's more like 2% performance
decrease... I will try to find the article again.


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Old 05 Dec 2003, 10:03 am   #17 (permalink)
markjen
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Default Re: Premium fuel in the GX470 necessary?

> From some of the reports that I saw, it's more like 2% performance
> decrease... I will try to find the article again.


C&D is the only definitive test I've seen.

- Mark


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Old 05 Dec 2003, 07:09 pm   #18 (permalink)
sf/gf
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Default Re: Premium fuel in the GX470 necessary?


"Tsheer" <post.to@use.net> wrote in message
news:PsVzb.30772$9O5.26772@fed1read06...
>
> "sf/gf" <sf90006@kart.com> wrote in message
> news:ObVzb.29152$sb4.17536@newsread2.news.pas.eart hlink.net...
> >
> > <wideglide01diespammers@cox.net> wrote in message
> > news:rflvsvsul9klcrf91ohfb8tra90a2dnv3m@4ax.com...
> >
> > >
> > >
> > > You *can* damage your engine by going with too *high* of an octane
> > > fuel for an engine that's not designed for it. Higher octane is to

> >
> > >
> > >
> > > ************************************************** ********************
> > >

> >
> > Please explain how using too high of an octane fuel can damage an

engine.
> > Although it may not make sense from an economic viewpoint, the only
> > difference between low octane and higher octane is that higher octane

> burns
> > slower (which is why it pings and knocks less). Some say higher octane

> also
> > has higher detergent levels, but I have never been able to verify this.
> >

> Gas doesn't burn "slower" or "faster". The octane rating is relative to
> the temperature
> at which the gas burns. Higher octane gas combusts at a higher

temperature
> than lower
> octane gas. Compression heats the fuel/air mixture, and if the octane

level
> is too low
> for the engine, the fuel/air will combust from the compression heat before
> the spark plug
> ignites it. That causes knocking.
>
>


Agreed. But the flame front actually takes longer to advance (milliseconds)
so there is a slower burn. At least that is how it was explained to me by
my Technology instructor in college. Also, think about diesel fuel for a
moment. Diesel fuel is a light fuel oil and has a lower octane that
gasoline (actually diesel fuel is measured in cetane, if I recall correctly)
It would take a much higher temp to cause diesel fuel to ignite than it
would gasoline, yet by your reasoning the opposite should occur.


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Old 06 Dec 2003, 05:28 pm   #19 (permalink)
Car Guy
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Default Re: Premium fuel in the GX470 necessary?

I would suggest you look at the owners manual and see what is REQUIRED (i.e. you MUST use) and what is RECOMMENDED (i.e. what is BETTER to use). I tend to follow the recommended route for fuel and maintenance and in a bind, will follow the required.

Not to sound curt, but if you can afford the car, surely, you can afford to gas it with premium :^)
"James P. Clark" <james.clarkANTI@SPAMadelphia.net> wrote in message news:zywzb.8695$zL1.1747283@news1.news.adelphia.ne t...
I've got a GX470 on order and should be picking it up next week. I know that Lexus recommends premium gas be used, but I'm wondering if there would be ill effects in using regular octane gas instead?

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Old 11 Dec 2003, 10:20 pm   #20 (permalink)
Matt Fournier
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Default Re: Premium fuel in the GX470 necessary?

It all has to do with the compression ratio of the motor in your car. The higher the compression ratio, the higher the octane you will need for that motor, with the results of higher horsepower per cubic inch. If you use to low of an octane, it will or can cause detonation and will cause problems with the piston rings in the motor. I definitely recommend using the octane required for the car because that's what the engine is designed for.

This is why diesel doesn't need spark plugs to ignite. The octane is so low and the compression ratio in those motors are so high that the diesel self ignites. Pretty complicated, I've learned because I use different fuels for drag racing, check out more at this website
http://auto.howstuffworks.com/question90.htm

"James P. Clark" <james.clarkANTI@SPAMadelphia.net> wrote in message news:zywzb.8695$zL1.1747283@news1.news.adelphia.ne t...
I've got a GX470 on order and should be picking it up next week. I know that Lexus recommends premium gas be used, but I'm wondering if there would be ill effects in using regular octane gas instead?

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Please remove all UPPERCASE letters in the reply email address!
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