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
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:02:06 EDT