At 11:15 AM 1/12/2002 -0800, you wrote:
>Isn't multi-grade oil the cold weight with additives to make
>it work differently when hot? In other words, 10W-30 is SAE
>10 weight oil that acts like SAE 30 when hot.
>
>Seems like any additives would break down over time, and it
>would revert to 10 weight oil if you left it in too long.
Correct, but it will take a very long time and many-many miles for that to
happen to a modern oil. This is however one of the reasons that oils like
10w40 (rather than 20w40) where there is a wide difference between the
"hot" and "cold" grade may be best to be avoided for hard driven cars- they
rely too much on the additives. This is one of the main advantages of
synthetics: they rely very little in viscosity additives, so you can
extend the drain intervals.
>Every owner's manual I've ever seen links oil to climate
>conditions. If you're in a mild area single weights are
>great; for most of us with varying climates we need the
>cold-start advantage of multi-grade.
Yes, you will be fine with a single-weight 30w or 40w if you lived, say,
in Hawaii. But even then, unless you plan to extend your drain interval,
why suffer the heavier startup wear caused by the "hesitation" of the 30w
to circulate when cold-started. These type of oils are usually quite
cheap, so there is also little incentive trying to extend your drain
interval...
D^2
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