Re: 5W-30 on the Autobahn?

[John Bolhuis <bolhuijo@xxxxxxxxxxxx>]

On Fri, 9 Nov 2001, Henri Baccouche wrote:

> >  Let's not forget that the important number is the 2nd one, i.e. the
> > 30 in 5w30.  A 5w30 behaves like a 5 weight when cold, and behaves
> > like a 30 weight oil when warm.
>
> I always understood it as a 5w oil capable of handling 30w operating
> temperatures. It's still a 5w on the freeway........on every hot day.
> It does not thicken to 30w.......

 Put more precisely, it's a 5w oil with long chain polymers that
unwind at working temperature to prevent the oil from thinning as much
as it normally would.  Thus, a 5w30 only thins out as much as a
straight 30w oil would when hot.  You're right, it does not thicken,
but neither does it thin out like a straight 5w oil.  That is why they
key point is that 5w30 oil behaves like a 30w oil when hot.
 As an aside, those long polymers that give the oil its dual
personality can be sheared into shorter ones under mechanical stress
and heat, effectively thinning the oil.  Thus it is to your benefit to
find a "shear stable" oil that will not break down quickly.
Synthetics are a good choice.

> >  Furthermore, a properly designed motor has internal clearances
> > specified with the designated lubricant in mind.  A motor designed for
> > thinner oil should last just as long as one designed for thicker oil,
> > provided they're using the right oil. As long as the oil film is
> > maintained between the moving parts, you gots no problems.
>
> Agreed, the question is when a 5w or a 0w is specified........is it selected
> for maximum gas mileage over maximum durability ?
>
> Funny, how manufacturers never "crow"
> about durability.......

 People like us on the outside will probably never know the
durability/mileage equations that manufacturers choose.  But if BMW
engines all started killing bearings and burning oil at 70k miles
since switching, you can bet it would start a sh*tstorm that people
wouldn't forget for a long time.

drive well...
- --
 "It is an honor to be Cookie Monster."
   -Sesame Street spokeswoman Audrey Shapiro

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