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Re: 5W-30 on the Autobahn? -- Long...
- Subject: Re: 5W-30 on the Autobahn? -- Long...
- From: "KOHLBRENNER,MICHAEL (A-hsgAndover,ex1)" <michael_kohlbrenner@xxxxxxxxxx>
- Date: Tue, 13 Nov 2001 08:54:46 -0700
Hi,
The Marks' Standard Handbook for Mechanical Engineers has a nice
section on Engine oils. The following is a summary of this as it
pertains to this topic.
Oil "Grades" are specified using standards established by the SAE
(Society for Automotive Engineers). Referring to the numbers on oil
bottles as "viscosities" is quite common, but a misnomer. As has
been discussed, the actual viscosity of these fluids varies widely
with temperature. And yes, the "W" in multigrade oils does stand
for "Winter". These are oils whose weight is specified by their
viscosities at 0 degrees F. Nonwinter oils are specified by their
viscosities at 210 degrees F. Thus, a multigrade oil has a
viscosity at 0F in the range of the Winter grade spec and has a
viscosity at 210F in the range of the Nonwinter grade.
Graphically, it looks like this:
\__
\__
\__
\__
\____ \__
\_-*-__ __5W30 \__
\__ -*-__/ \__
\__ -*-__ \__
V \__ -*-__ \__
I \__ -*-__ \__ __30
S \__ -*-__ \__/
C \__ -*-__ \__
O \__ -*-__ \__
S \__ -*-__\__
I \__ -*-\__
T \__ \
Y \__ __5W
\__/
\__
\__
\__
\__
\
----|---------------------------------------------------|---
0 210
TEMPERATURE, DEGREES F
While there is no viscosity scale shown, it is logarithmic.
To complicate things even further, there is a different viscosity
measurement used at 0F than at 210F. Officially, the viscosity of
Winter oils at 0F is measured in centipoise, while the "normal"
oils are measured at 210F in centistokes. Conversions between the
two scales is approximate. Using these conversions, a 5W30 oil has
a viscosity at 0F of less than ~1300 centistokes. At 210F, it has
a viscosity between 9.6 and 12.9 centistokes.
A 50 weight oil has a viscosity of between 16.8 and 22.7 centistokes
at 210F.