[no subject]

So, you can see that even a 5W oil is pretty darn thick at cold-start
temperatures when compared to a 50 oil at operating temperatures.

Go ahead and drain that 20W50 oil when it is really hot.  It comes
out like water.


From: Henri Baccouche <henrib@domain.elided>

> ... the question is when a 5w or a 0w is specified........is it
> selected for maximum gas mileage over maximum durability ?

The impression that engine manufacturers were focused on the 5W or
0W part isn't quite correct.  It is the normal operating conditions
that they were focused on -- the part where the 30, 40 or 50 matters.

Through the improvement of production tolerances inside today's
engines, manufacturers are able to design in tighter clearances.
They have also gotten better at controlling heat in the engine
through better cooling control and the use of materials, like
aluminum, that have better heat conductivity properties.  There is
also better control of the combustion process with modern electronic
fuel injection systems and better overall engine efficiency to turn
more of the fuel energy into useful work and less into waste heat.

All of this allows them to use thinner oils and still keep oil
pressures in line.  This is how we end up with a 30 weight oil at
operating temperatures, rather than the old 40 and 50.

Once you've gotten down to a 30 weight oil, the 5W part comes along
for free.  In terms of oil quality, a 5W30 is no worse than a 20W50,
assuming that they are each used in engines designed to use these
respective grades.  They both have close to the same "spread" which
results from close to the same amount of those polymers that were
mentioned that create the multigrade properties.  Actually, a 10W40
oil is among the worst of all the standard grades in this regard in
that it contains the most of these polymers.  As was mentioned, this
is NOT a case where "if a little is good, a lot is better".  Also,
this is a case where synthetics are superior, since they have
multigrade properties in their base form and need little, if any, of
these polymer additives to achieve a 5W30 or 15W50 spread.  If the
synthetics didn't cost so much, I imagine that most engine
manufacturers now specifying 5W30 would start specifying 0W30.  The
30 part wouldn't change, but the part representing cold start
properties would.

My guess is that the engine manufacturers work to improve fuel
economy WITHOUT significantly impacting longevity.  Whether or not
people realize it, even those who buy/lease brand new cars and get
rid of them after 40K-70K miles benefit from an engine that will
last 200K miles.  It is called "Resale Value".  I know it's not BMW
focused, but by way of illustration I will submit the following
personal experience with another brand that has been specifying 5W30
oils for at least a decade.

My wife needed a new car back in early '96.  We would have had no
problems paying ~$19K for a brand new '96 Accord Sedan -- 4 year old
versions with ~70K miles were selling for over $12K.  Do the math --
a car with the best third of its life gone selling for ~2/3 of
original price?  That's what I call resale value and it is part of
why folks flock to these cars -- they know that they can use them
for a couple of years with little maintenance cost and then unload
them for a good price onto the hungry used market just before they
need a $350 timing belt change.  And by the way, we ended up paying
dealer invoice of $20K for a brand new leftover '95 Accord Wagon in
early '96.  Now, six model years old with 98K miles and a fresh
timing belt installed by yours truly, it has a Kelly Blue Book Private
Party Sale value of about $7500.  This car is good to go for another
100K miles on nothing but 5W30 (or maybe 10W30 for the summer).

Unfortunately for those buying new, the longevity of these sturdy
German cars hasn't produced the same result.  However, for those
buying used, it is great.  I got my '92 535i with at least half
its 200K+ life expectancy remaining for about 1/4 of its original
cost.  Now that is value!

I hope this helps.

Regards,
Mike Kohlbrenner

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