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what's up with the oil #'s???


 
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turd
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Joined: 27 Jul 2005
Location: cookvegas

PostPosted: Mon Aug 08, 2005 1:04 pm    Post subject: what's up with the oil #'s??? Reply with quote

hey guys,

Trying to find a good explanation of what the oil weight numbers mean. Not looking for "35W-20 is better than 54W-102" but I am looking for what the numbers mean in viscosity, temperature tolerance, breakdown time, slickness etc.

Also, what about gear oil weights? Synthetic?

Anybody that knows or can point me to a link will be appreciated.
thanks
turd
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Mon Aug 08, 2005 3:09 pm    Post subject: Reply with quote

The W in oil numbers has nothing to do with weight. It stands for Winter. The numbers have more to do with thier pour viscosity at certain temps.

One of the best blue color sites I know of is Bob is the oil guy site. There is a ton of great info about oils, lubes etc and the different varieties available in mineral or synthetics.
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Mon Aug 08, 2005 4:39 pm    Post subject: Reply with quote

Google is you friend...from How Stuff Works.

On every bottle of motor oil there is a seal that gives you three pieces of information:

The API service rating
The viscosity grade
"Energy Conserving" indicator (it either is or it isn't)
The API service rating is a two-letter rating that tells you the type of engine the oil is meant for (gasoline or diesel) and the quality level.
The viscosity grade (for example, 5W-30) tells you the oil's thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity -- it is thin and flows easily. Honey has a very high viscosity -- it is thick and gooey.

The standard unit used to measure viscosity is the centistoke (cSt). According to the Automotive and Industrial Lubricants Glossary of Terms:

Viscosity is ordinarily expressed in terms of the time required for a standard quantity of the fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Since viscosity varies inversely with temperature, its value is meaningless unless accompanied by the temperature at which it is determined. With petroleum oils, viscosity is now commonly reported in centistokes (cSt), measured at either 40C or 100 C (ASTM Method D445 - Kinematic Viscosity).
The centistoke rating is converted into the SAE weight designation using a chart like the one shown on the Superior Lubricants Web site.
Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature. This page from the Sci.Electronics.Repair FAQ offers the following very interesting description of how the polymers work:

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.
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turd
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Joined: 27 Jul 2005
Location: cookvegas

PostPosted: Wed Aug 10, 2005 2:57 pm    Post subject: Reply with quote

Cool.

Thanks
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