Oil question-D^2?

[dardal@xxxxxxxxxxxxxxx]

In addition to Mike P.'s comments, the reason why 5w30 is not recommended in 
hot weather is the following.  The 5w30 uses a 5w base stock and in order to 
get to the 30w hot viscocity, they need a LOT of viscocity additives.  Since 
these additives deplete with extended hot operation, this oil will get thinner 
faster.  If it was a synthetic, it would rely a lot less on the additives, so 
it would be OK.  Mobil 1 has a 0w50 for super cold climates and hard driving.

Clarification for those somewhat confused with these terms:  Fisrt of all, 
viscocity is a term that shows how easily the fluid flows.  The higher the 
number, the slower the flow, but the better the "lubricity" of the oil, or its 
ability to protect sliding surfaces.  A 10w, or 20w, or 30w is basically a 
relationship between temperature and viscocity.  All oils loose viscosity with 
increasing temperature, and each number designates this relationship for a 
conventional mineral base stock (base stock=just the oil, no additives).  Then, 
sometime just after WW2 they came up with multi weight oils that thanks to 
these tiny little additive molecules that expand when they get hot, they 
managed to reduce the rate at which the oil looses viscosity with increasing 
temperature.  These additives are poured into the low number base stock (ie 10w 
to enhance it into a 30w for 10w30).  So, now, if you made a graph of 
temperature on the x and viscosity on the y, all old type of single weight oils 
would be a bounch of down-slopping paralel lines, with the heavier oils higher 
up.  The multi weights would still be down slopping, but less so, and would 
intersect the single weights (hard to invision without a picture).  As a 
result, they had to come up with a different method to define the viscocity of 
the new oils.  So, a 10w30 according to the new naming system would have the 
vicocity of an old 10w at 32F, and at 212F, while its viscocity would be much 
less, (more than 5 times lower than at 32F), it would be comparable to 
a "conventional" 30w.  Further, as the temperature keeps on climbing, the 
viscocity loss will be far lower for the multi weight, a very important factor 
when it comes to lubricating the piston rings at TDC (the cylinder liner at TDC 
will reach over 250F even for light loads and far hotter at high speeds and 
loads).  This resistance to viscocity loss with temperature is 
called "Viscocity Index" and that's one of the huge advantages of synthetics 
(Mobil 1 15w50 is one of the best).  That's one of the reasons why synthetics 
are superior for hard driving, and multi weights are superior to single weights 
for ... any driving!  

D^2
Quoting Rob P <fristpenny@xxxxxxxxxxx>:

> I was checking my owner's manual & it has that generic temperature to
> oil 
> viscosity chart.
> If the 10 is the "cold" weight and the 30 is the "hot" weight, then why
> is 
> 10w30 recommended for warm weather and 5w30 is not? It seems to me that
> they 
> should be the same as far as heat is concerned. Do I have it backwards?
> Rob
>