Date:         Wed, 26 Apr 1995 21:11:27 -0500
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         dbax@mindspring.com (Donald Baxter)
Subject:      Re: Octane ratings

I won't waste bandwith repeating others comments but I will share my
experiences.  I think engine longevity depends much more upon the sort of
oil, and frequency of oil changes than gasoline octane ratings.  My '85
Jetta GL was only filled with regular unleaded, usually Shell, Chevron or
Texaco.  The oil was changed religiously every 7,500 miles with Mobil
1--ordinarily I would be changing at half this interval but synthetic is
expensive and what the hell, they used to claim Mobil 1 was good for 25,000
miles.  The car ran without a hitch until it separated from me in a
relationship at 135,000 miles, by without a hitch I mean it consumed (or
leaked) approximately 1/2 quart of oil between changes.  Pretty good
testimonial, I'd say--I never expected it to last that long.  The car is
still running strong at 150,000 miles.  I consider broadsiding it every time
I see my former S.O. driving it around--come to think of it, perhaps I
shouldn't have taken THAT good of care of the car (but I'm NOT bitter :)).

My '92 Passat Variant runs on 92-93 octane and I use it because the owners
manual recommends this.  Although the ignition map will adjust for running
on regular unleaded, and it gets better fuel economy (fairly significant,
around 2 mpg or more), it does demonstrate minor ignition detonation on
accelaration.  This detonation disappears almost immediately after the knock
sensors work whatever magic they work.  I do use regular unleaded on long,
expressway trips since acceleration isn't as critical and the gas mileage is
better.  This vehicle has 50,000 miles on it and has used oil since new
(grrrr) so it's longivety related to gasoline would be impossible to
determine.  Its longevity with me, however, isn't--it's for sale (any takers?).

The '85 Vanagon demonstrates no ignition detonation with regular unleaded,
achieves no better than 18 MPG regardless of what octane the fuel is so I
guess I'll save my money.  Regular is around $1.04 here in the Atlanta Metro
Area versus $1.25 for premium.

I think that the enemy of engine longevity is detonation, combined with poor
maintenance.  I'd say, if it doesn't ping on the cheaper stuff, use it.  But
don't drive it around pinging!
_________________________________________________________
Donald Baxter  <dbax@mindspring.com>  Atlanta, Georgia
404.874-3292 (home)
404.447.6831 (work)

_________________________________________________________
You know why the reason why some nights you don't have a dream?
When there's just blackness? And total silence?

Well, this is the reason:
It's because on that night you are in somebody else's dream.
And the reason you can't be in your own dream because
you're already busy in somebody else's dream.

                                -Laurie Anderson, Stories from the Nerve
Bible (1993)