Originally Posted by Prelude543
so the viscosity rating in this case is 10w40 which actually means what viscosity your engine will pump at. The W stands for winter, not weight. you can check yourself on wikipedia as a quick ref should you not believe me. cheers for the oil tutorial anyway though.
Hi there...OK first off, I was just using 10W30 as an example. And I never said that the "W" stood for weight.
And looky here, taken straight from Valvoline.com - Home Page
Multigrade oils typically begin as base oils, such as 10W. Then viscosity-index modifiers (polymers) are added in an effort to stabilize the viscosity. This allows a 10W40 oil to flow like a 10W at cold temperatures and a 40W at higher temperatures.
In other words, multigrade oils are formulated to pass viscosity tests across a range of weights."
And another site, Auto Repair Advice
(probably not as trustworthy, but it explains my point):
"Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot.
Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils
. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil.
You will hear them referred to as multi-viscosity, all-season and all-weather oils. An example is a 10W-30 which is commonly found in stores."
And from Howstuffworks "What does the weight mean on a can of motor oil?"
"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."
You can take your wikipedia and shove it up your...well you know.
Sorry that the thread has turned into a pissing contest, but I couldn't let this guy spew the wrong information all over it.