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Viscosity ratings are for ambient temperature flow, not operating temperature flow.
http://www.autoeducation.com/autoshop101/oil-change.htm
Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).
Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.
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. When choosing oil, always follow the manufacturer's recommendation
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Most petroleum oils have pour points in the range of -15 to -35 degrees F. That means that their borderline pumping temperature is, at best, around -15 degrees F and probably closer to 5 to 10 degrees F. So, if you're running a petroleum oil, don't expect to go out and start your car at 0 degrees and have it purr like a kitten. It's going to spit and sputter and kick and scream for a few minutes.
Why do you think that is? It's not getting any oil up into the engine. It's like trying to suck molasses through a tiny straw in an Alaskan January. There's literally nothing keeping the metal components in your engine from tearing each other apart. Every time you start your engine in conditions like this, your engine dies a little bit more.
Now that I've bored you to death, you can check out this link as well if you're still not convinced.
http://www.amsoil.com/testimonials/lotito.htm
Greg
'19 Genesis G70 3.3t AWD '88 Chrysler Conquest TSI
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