I'm not a mechanic, and don't play one on TV or anywhere else. However,
I feel your same discomfort for 5W oils. When I got my new 2003 GMC 1/2
ton truck, the owners manual recommended 5W30 oil but said 10W30 was OK
if you couldn't find or didn't want to run 5W. Nearly 40 years of
driving various cars and motorcycles makes me inherently distrustful of
such light oil in an I/C engine, and I have run what ever 10W30 is on
sale (by the case) in my truck and my wife's Subaru, changed every 3K
miles, and using a good NAPA filter. I think, as you do, that the 5W
oil is recommended strictly from a gas mileage standpoint.
I also don't really care for 10W40 weight oils; I have read enough to
have reached the conclusion that the 40 weight oils have a much higher
polymer to petroleum ratio and break down faster. YMMV, and if you like
to run them, go right ahead.
Before everyone was so concerned with high fuel mileage, I ran 15w40
"all fleet' diesel rated oils (Delo 400, Rotella, etc) in everything I
owned, from tractors to motorcycles to cars and trucks. I no longer run
it in my car or truck, but I continue to use it in everything else. Now
that our Subaru Forester has 100K miles on it I may start running 15w40
in it, too. Has anyone got any experience running 15w40 in a late model
GM Vortec engine?
I'd be interested in hearing what everyone else thinks. Nothing like a
good oil thread.
Dave C
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
>
>
>
> A democracy will continue to exist up until the time that voters
> discover they can vote themselves generous gifts from the public
> treasury.
>
> Author unknown
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