Date:         Sun, 15 Oct 2000 15:40:49 -0300
Reply-To:     Jean-Guy Savoie <jgsavoie@NBNET.NB.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jean-Guy Savoie <jgsavoie@NBNET.NB.CA>
Subject:      should 10W-40 be avoided?
Content-Type: text/plain; charset="iso-8859-1"

Hi all

I finally found the reference to 10W-40 not being a good idea : see
http://members.aol.com/johnbmtl/faqoil.html were this is said, amongst other
things:

"Multi viscosity oils work like this: Polymers are added to a light base
(5W, 10W, 20W), which prevent the oil from thinning as much as it warms
up. At cold temperatures the polymers are coiled up and allow the oil to
flow as their low numbers indicate. As the oil warms up the polymers begin
to unwind into long chains that prevent the oil from thinning as much as
it normally would. The result is that at 100 degrees C the oil has thinned
only as much as the higher viscosity number indicates. Another way of
looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that
will not thin more than a 50 weight would when hot.

Multi viscosity oils are one of the great improvements in oils, but they
should be chosen wisely. Always use a multi grade with the narrowest span
of viscosity that is appropriate for the temperatures you are going to
encounter. In the winter base your decision on the lowest temperature you
will encounter, in the summer, the highest temperature you expect. The
polymers can shear and burn forming deposits that can cause ring sticking
and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics
excluded) to achieve that range. This has caused problems in diesel
engines, but fewer polymers are better for all engines. The wide viscosity
range oils, in general, are more prone to viscosity and thermal breakdown
due to the high polymer content. It is the oil that lubricates, not the
additives. Oils that can do their job with the fewest additives are the
best.

Very few manufactures recommend 10W-40 any more, and some threaten to void
warranties if it is used. It was not included in this article for that
reason. 20W-50 is the same 30 point spread, but because it starts with a
heavier base it requires less viscosity index improvers (polymers) to do
the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity
index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no
viscosity improvers in their 5W-30, and I assume the new 10W-30. Follow
your manufacturer's recommendations as to which weights are appropriate
for your vehicle."


For all those interested

JGS