I'm only a shadetree mechanic, but I've given this subject quite a bit
of thought and research.
Synthetics, arguably, are more durable than mineral oil as far as
breakdown from shear forces. However, they will accumulate contaminants
from blowby and water (acids, etc.) similar to mineral oil. Therefore,
frequent oil changes are best with either oil (and, remember, there's a
time recommendation as well, usually every 3 months regardless of
mileage, though I've never been religious about following that).
Ironically, the shorter molecules of mineral oil may be better at
scavenging contaminants than synthetic.
I did decide if I had to do a lot of highway driving--for a job, for
instance--say, 2,000-3,000 miles a month, I would use synthetic oil and
extend the oil change to 6,000 miles or more. You get fewer
contaminants--and vaporize the water in the oil--if you take mostly long
trips (and having to change the oil every month would get old, and
expensive). I know a guy who commutes from Madera, CA to the Bay Area
every day in a Honda Civic (about 200 miles total), which is still
running strong with Mobil 1 at nearly 300,000 miles and oil changes
every 12,000 miles.
Ford recommends their 5W-20 semi-synthetic for my new Mustang--you think
30W is thin!--and oil changes every 7,500 hundred miles regardless of
usage. I gave it a lot of thought and, since I drive mostly city miles,
decided to go to a 5,000 mile interval. And, I stuck with the
5W-20--against my instincts, at first--when I found I can get it for
$2/qt at WalMart. Yes, the manufacturers need better CAFE numbers, but
new engines are built with such tight clearances a quality thinner oil
will be fine. I believe Ford's engineers know what they're doing--even
if their accountants don't ;)
Bob
Karl Vacek wrote:
> I've been running the manufacturer-recommended 5W-30 in my 2 modern cars, both
> current-generation American V-8's, each purchased used with 25,000 and 36,000
> miles on them, and I've used synthetic since we bought them.
>
> I've always been leery of such thin oil, despite the manufacturers' assurances
> that the engines are designed for it. Stands to reason that they want their
> CAFI numbers as high as possible, and thin oil probably gives them a little
> extra mileage in the fleet.
>
> Recently I read a lengthy article about automotive oil (senior moment - darn
> if I know where saw it), and the crux of the story was that 5W-30 is indeed
> really too thin, particularly in the summer, and running at least 10W-40 is
> far better for the engine. Maybe 5W-30 in the dead of winter (I'm in the
> Chicago area), but not in the summer.
>
> The author also said (and I tend to believe this even though I'm still using
> synthetic for now) that synthetic is really a waste on most cars in typical
> use, because the additive packages in regular oils are so good today, and
> changing at 3,000 miles (which I do with the synthetic anyway) gives so much
> protection that synthetic just can't do any better.
>
> This list has some mechanics working on current-type cars - what do you say
> about these issues ??
>
> TIA
> Karl
>
>
>
--
*******************************************************************
Bob Spidell San Jose, CA bspidell@comcast.net
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