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RE: Pep Boyz - Synth vs. Dino

I don't want to revive a thread that might be better left alone, BUT, if I'm
not mistaken was there not a lengthy discussion about how "going synthetic"
after using "dino" would/could result in seal deterioration/failure and
catastrophic oil leaks?

I know that there were arguments both FOR and AGAINST this theory (de-waxing
theory etc.) and actual personal accounts of Mercedes engines turning into
oil sieves and Audis running amuck after going synthetic, and others that
refuted such incidents.

My question is, if there's even a chance that this might occur after "going
synthetic", I think it would weigh heavily upon the "cost effectiveness" of
synthetic oil would it not?  I bought my car used, so I didn't have the
option of running synthetic from new.  If I did, I think I would run
synthetic, but given the horror stories of "going synthetic" mid-course...
Is the margin of thermal protection/viscosity difference worth the risk of
having a seal fail prematurely?  Opinion?  Did I miss something?

Dan Sinclair
1988 Audi 90, 69K mi.
Photo and details online at:

-----Original Message-----
From: owner-quattro@coimbra.ans.net
[mailto:owner-quattro@coimbra.ans.net]On Behalf Of Scott Fisher
Sent: Thursday, April 08, 1999 11:00 AM
To: Audi List
Subject: RE: Pep Boyz

Steve Buchholz says:

> If I were making the choice I would be more likely to
> vote for not having to replace the engine ... and be
> oblivious to the $$$$ I've tossed in the $h!tter by my
> lower fuel economy ...

Old saying: "Oil is cheaper than metal."  Is gasoline?  Let's look.

I've read fuel economy savings reasonably quoted on the order of 1-2% by
going with lightweight oils.  A few moments with a calculator yields the
following results (which I'm going to express in miles per gallon and
dollars; I can waste enough time to do that, but you'll have to waste
your own time figuring it out in your local measurements and currency

Let's look at a car with a baseline average fuel economy of 20 mpg, over
a 100,000-mile interval.

100,000 miles therefore takes 5000 gallons of gas.

Raising the fuel economy by 1.5% (to 20.3 mpg) uses 4926.1 gallons of
gas to go 100k miles.

Rounding off that 0.1 gallon gives us a 704-gallon savings over 100,000

At the price of the gas that's in my tank today ($1.89/gal), that's a
savings of $1330.56.  Probably not enough to replace an engine, though
possibly more than the value of a 100k-mile Audi considering that these
cars shed resale value the way a white cat sheds on a black velvet

Now, I've ignored a LOT of variables (inflation in oil/gas prices over
the time represented by 100k miles, added cost of oil consumption due to
increased wear caused by lighter-weight oil, etc. etc. etc.)  And I
haven't factored in the consideration that the reduced drag from lighter
oil essentially gives you either another 1-2% of economy *or* another
1-2% of power, but not both at the same time, and we all know what
*we'd* do with the choice.)

Note that one of the initial incentives for using synthetic oil is that
the molecules were designed to provide both low friction AND high shear
strength/thermal stability, again on the order of a few percent -- not
magic, just thorough engineering.  You may reasonably expect both
improved economy and improved engine protection by going with a 10W-50
synthetic, but at what cost?

That same 100k mile service interval, assuming 3000 miles between oil
changes (we're all maniacs on this bus, right?), gives us 33.3 oil
changes; let's assume we made one longish trip and didn't change the oil
for a couple hundred miles and round it to 33 oil changes.  I'll also
use 4 quarts per change in these calculations, as that's how much new
Castrol I poured into the GT last Saturday.  And finally, I'll use an
average cost per quart (again, US figures) of $1.25 for dino and $3 for
synth (ignoring filter costs).  (Those prices may be way off; I'm
ashamed to say I don't remember what each quart of oil I bought last
Saturday set me back.)

This gives us, over that 100k-mile service interval, a cost of $167 or
so for oil changes with mineral oil.  The cost jumps to $396 for $3
synthoil, meaning that the person who changes his or her oil every 3000
miles with synthetic oil will probably still come out ahead over 100k
miles -- even assuming only a 1.5% increase in fuel economy and the
improved engine protection of a higher-viscosity oil.  So it sounds like
you're still about a thousand dollars ahead after 100k miles by using
$3/qt synthoil, because you save the gas and you don't have to replace
the engine.  (And yes, I know Audis can go a lot longer than 100k miles
between engine replacements; I just used these numbers because they're
easy to think about.)