That's the kind of info I was lookin for....Thanks Bob.
"Bob Tom" <tigers@bserv.com> wrote in message
news:5.0.2.1.0.20010713075101.009ee910@bserv.com...
> At 08:30 PM 7/12/01 -0400, you wrote:
> >My understanding is that the "thicker" the oil...the more protection from
> >friction. I come from the old school which says 10W-30 in the winter
> >(slightly thinner to help with cold starts) and 10W-40 in the summer
> >(thicker=more protection). But MOBIL-1 has other grades such as 5W-50
etc. I
> >ask about the 'grades' because a buddy of mine used the 5W in his
> >truck???..and when I went to get oil the other day, I found that MOBIL-1
> >carries a bunch of different grades and types (ie tri-synthetic,
synthetic
> >along with the different grades) To behonest, I'm not sure what the
numbers
> >represent, although I would imagine that there is a MAX viscosity which
you
> >can place in your vehicle...above which would be TOO thick and may lead
to
> >blown seals etc. --SNIP--Kevin
>
> Kevin
>
> I apologize if some of this is redundant but I hope the lengthy reply will
> be useful.
>
> The way that oil viscosity is measured is by its weight. In this case,
> "weight" refers
> to the thickness of the oil. Any liquid has some viscosity and that
> viscosity changes
> depending on its temperature. Usually, viscosity (thickness) decreases as
> temperature
> increases.
>
> Engines need a thin oil at startup, so that it can get to the engine
> components quickly,
> but it needs a thicker oil when the engine is hot because a thin oil
> becomes too thin.
> This is why engine oils are supplied as dual-grade weights. When you see
> 10W-30
> on a quart of oil, it means that it acts like 10 weight oil when it is
cold
> (the "W" means
> winter, say -10C), but acts like 30 weight oil when hot (100C). This is
> not to say that
> it is actually thicker when it is hot. Hot 30 weight oil is thinner than
> cold 10 weight oil.
> Even so, it still helps provide the benefits of both types of oil
depending
> on its temperature.
> So 0W-30 oil acts like 0 weight oil when cold, but maintains a 30 weight
> viscosity when hot.
>
> I think of it this way: when your engine is hot, there is basically no
> difference between
> 0W-30, 5W-30, and 10W-30 oil. They are all acting like 30 weight oil at
> this point. It's
> at cold startup, when almost all engine wear occurs, that the viscosity is
> different.
> The 0 weight oil will get to the engine components quicker than the 10
> weight oil, but in
> reality cold 0 weight oil is still thicker than hot 30 weight oil. On the
> other hand when the
> engine is cold, there is no difference between 10W-30 and 10W-40
> oil. However when
> the engine is hot, the 10W-40 oil is thicker than the 10W-30. This is why
> single-grade
> oils are very bad for normal driving. Straight 30 weight oil is way too
> thick when cold to
> properly lubricate the engine. One way to use single weight oil is to
have
> an oil pan
> heater to bring the oil up to operating temperature (about 140F or 60C)
> before the engine
> is ever started. This type of oil is ideal in race engines with pan
heaters.
>
> As far as what oil viscosity is best, it depends who you ask. I believe
is
> that engine oil
> maintains its viscosity better than ever (showing my age) and synthetics
> maintain it the
> best. In my opinion, the best viscosity for all weather is 5W-30. The
> reason is that both
> 5W-30 and 10W-30 breakdown at about the same point. Lighter oil can get
> into places
> that the heavier oil cannot and will get there more quickly, even when
> cold, so why go
> heavier? The only reason would be leaks. If you have oil leaks, a heavy
> oil will go through
> them more slowly. That is why you can buy "No-Smoke", which is basically
> sludge to
> thicken your oil. If your engine is sealed well, feel free to try Mobil
> 1's 0W-30 oil. If that "0"
> really makes you nervous, stick with 5W-30. 10W-30 is un-necessarily
thick
> when cold.
>
> HTH
> Bob
>
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