Is It Necessary To Use Premium?

[davesixtythree]

Hi All, Just got a used 04 forester XT with 55,000 miles. Question, is
it really necessary to use prem. gas or will mid grade or regular do? I
will probably buy the prem. but I put on a lot of miles and saving some
$$$ would help. Question, with the Toyota Rav4 I traded in at 190,000 I
changed oil at 6,000 is this ok to do with the turbo? I need to get at
least 200,000 mile on this car. Any advice on Subaru would be most
welcome. Thanks

 

[bigjim]

Premium is not necessary. You may experience better performance but at
a level you'd only notice on a dyno or by hooking into computer.

 

[Kurt Krueger]

Hi All, Just got a used 04 forester XT with 55,000 miles. Question, is
it really necessary to use prem. gas or will mid grade or regular do? I
will probably buy the prem. but I put on a lot of miles and saving some
$$$ would help. Question, with the Toyota Rav4 I traded in at 190,000 I
changed oil at 6,000 is this ok to do with the turbo? I need to get at
least 200,000 mile on this car. Any advice on Subaru would be most
welcome. Thanks

Going with the manfacturer's interval is usually a good bet.

But, the difference in appearance of the valve train in an engine that
has had the oil changed at a 3,000 mile interval vs. 5,000 is amazing.
Enough that I've switched to a 3,000 interval.

But, my '83 Camry with 5,000 mile (or worse) oil changes now has 250K
miles. Lots of varnish on the valve train, but it doesn't seem to be
hurting anything.

 

[Stephen H]

If its a 6 cyl then manufacture says premium required.


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist
Currently working at a Subaru dealership

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/
http://www.familycar.com/Alignment.htm

 

[Uncle Ben]

If its a 6 cyl then manufacture says premium required.

The purpose of higher octane is to suppress "knocking," the pinging
sound you hear when the gasoline vapor ignites prematurely when
compressed in the cylinder. So try a tankful of regular and see if it
knmocks. If it does, go back to premium at the next fill-up.
Otherwise, you've won!

Uncle Ben

 

[Ragnar]

Hi All, Just got a used 04 forester XT with 55,000 miles. Question, is
it really necessary to use prem. gas or will mid grade or regular do? I
will probably buy the prem. but I put on a lot of miles and saving some
$$$ would help. Question, with the Toyota Rav4 I traded in at 190,000 I
changed oil at 6,000 is this ok to do with the turbo? I need to get at
least 200,000 mile on this car. Any advice on Subaru would be most
welcome. Thanks

You should stay with Premium for 3 reasons:

1. Reduced octane gas will cause the engine to knock
2. Reduced octane gas will cause the engine to retard timing, hurting
performance.
3. You'll get less mpg with lower octane gas.

 

[Bonehenge]

3. You'll get less mpg with lower octane gas.

Think beyond the pump price number.

My V6 Tacoma "recommends" premium. It gets enough extra mileage on
premium that the per mile cost is cheaper. It runs OK on regular, but
I do the math every time I fill up.

What a shock! The manual was meaningful! <G>

 

[CompUser]

16g2000cwy.googlegroups.com>, (e-mail address removed)
says...

The purpose of higher octane is to suppress "knocking," the pinging
sound you hear when the gasoline vapor ignites prematurely when
compressed in the cylinder. So try a tankful of regular and see if it
knmocks. If it does, go back to premium at the next fill-up.
Otherwise, you've won!

No, otherwise the ECU sensed the knocking (via
the knock sensor, imagine that) and retarded
timing to *stop* further knocking and engine
damage...reducing effective engine power output
in the process.

Now, does that still sound like a win?

 

[Yousuf Khan]

3. You'll get less mpg with lower octane gas.

Yup, which I've confirmed on my own car.

Yousuf Khan

 

[Uncle Ben]

16g2000cwy.googlegroups.com>, (e-mail address removed)
says...

No, otherwise the ECU sensed the knocking (via
the knock sensor, imagine that) and retarded
timing to *stop* further knocking and engine
damage...reducing effective engine power output
in the process.

I'm no automotive engineer, but I can't see how retarding timing would
stop the knocking, since the knock is caused by compression, not a
spark. As for engine damage, I am equally skeptical, although I accept
a slight loss of engine power.

 

[Carl 1 Lucky Texan]

I'm no automotive engineer, but I can't see how retarding timing would
stop the knocking, since the knock is caused by compression, not a
spark. As for engine damage, I am equally skeptical, although I accept
a slight loss of engine power.

Igniting the charge even furhter before TDC does not allow it the
opportunity to ignite from compression.

Carl

 

[Kurt Krueger]

I'm no automotive engineer, but I can't see how retarding timing would
stop the knocking, since the knock is caused by compression, not a
spark. As for engine damage, I am equally skeptical, although I accept
a slight loss of engine power.

It's a simple fact that it does. You can argue why, but advanced timing
will cause spark knock. Just talk to anyone who's worked on cars before
all the electronic controls, back when timing was controlled purely by
engine RPM and vacuum. Peak performance was obtained by advancing the
base timing as far as possible without knocking. If you advance too
far, serious knocking occurred.

Toyota used to have a small knob on the distributor called an octane
selector. It let you fine tune the timing ... you retard it if the
engine knocks. Or you can advance it for better performance on
premimum fuel.

 

[CompUser]

@j72g2000cwa.googlegroups.com>, (e-mail address removed)
says...

I'm no automotive engineer, but I can't see how retarding timing would
stop the knocking, since the knock is caused by compression, not a
spark. As for engine damage, I am equally skeptical, although I accept
a slight loss of engine power.

http://www.wellsmfgcorp.com/pdf/counterp_v4_i4_
2000.pdf

http://www.superchargersonline.com/content.asp?
ID=104

 

[Ed]

Kurt Krueger wrote:

Toyota used to have a small knob on the distributor called an octane
selector. It let you fine tune the timing ... you retard it if the

^^^^^^^^^^

This gave me a good laugh. I was just skimming through this thread and
was wondering why the playground name calling. Went back and re-read to
see what was going on. On understanding it still brings back high school
shop days and timing lights and twisting the distributor to advance the
timing.

 

[wrenden]

Kurt Krueger wrote:

^^^^^^^^^^

This gave me a good laugh. I was just skimming through this thread and
was wondering why the playground name calling. Went back and re-read to
see what was going on. On understanding it still brings back high school
shop days and timing lights and twisting the distributor to advance the
timing.

He he. Back in my drag racing days I connected a manual choke cable
to a distributor on my 47 Pontiac. Great fun.

wrenden

 

[nobody >]

Kurt Krueger wrote:

^^^^^^^^^^

This gave me a good laugh. I was just skimming through this thread and
was wondering why the playground name calling. Went back and re-read to
see what was going on. On understanding it still brings back high school
shop days and timing lights and twisting the distributor to advance the
timing.

It was known as "twist'er till she knocks and back off 5" (degrees that
is). Worked wonders back in those days!

 

[Just Facts]

Hi All, Just got a used 04 forester XT with 55,000 miles. Question, is
it really necessary to use prem. gas or will mid grade or regular do? I
will probably buy the prem. but I put on a lot of miles and saving some
$$$ would help.

Use what the manufacturer recommends.
If regular is called for you are wasting your money useing premium.

Question, with the Toyota Rav4 I traded in at 190,000 I
changed oil at 6,000 is this ok to do with the turbo? I need to get at
least 200,000 mile on this car. Any advice on Subaru would be most
welcome. Thanks

Again what does the manufacturer call for.
Usually turbo vehicles require more frequent oil changes.

 

[davesixtythree]

Thank you to all who posted replys. Please keep them coming. For the
record, for now Dec., Jan. and Feb I'll stick to the recommend prem.
gas then when I start going through 3 or 4 tanks a week I'll make a
study of the difference and report my findings. Thanks again for your
advice. Look for my next, the 60,0000 mile service question.

 

[Uncle Ben]

Igniting the charge even further before TDC does not allow it the
opportunity to ignite from compression.

Carl

Can we agree that knocking is caused by too early an ignition?

So advancing the timing would make the knock even worse.

Retarding the timing would do nothing, since the mixture would already
have ignited from the compression.

So I don't see how any adjustment to timing would eliminate knocking
due to low octane. (If it would, think of the money we could save.)

Uncle Ben

 

[Fuzzy Logic]

Hi All, Just got a used 04 forester XT with 55,000 miles. Question, is
it really necessary to use prem. gas or will mid grade or regular do? I
will probably buy the prem. but I put on a lot of miles and saving some
$$$ would help. Question, with the Toyota Rav4 I traded in at 190,000 I
changed oil at 6,000 is this ok to do with the turbo? I need to get at
least 200,000 mile on this car. Any advice on Subaru would be most
welcome. Thanks

http://www.canadiandriver.com/articles/jk/060118.htm

Generally if it asks for premium you should use it. The ECU can compensate for other fuel types but the engine
performance will suffer and likely any savings made at the pump will be eaten up by the poorer gas mileage.