I can't believe that people are still getting this wrong. The viscosity of an oil at operating temperature is always the higher number. The 5W or 0W is only the winter rating or viscosity as 0 degrees Celsius. Even youtube car "experts"
get this wrong.
ALL oils are thicker when cold, though ideally they should be a consistent viscosity at any temperature.
Quote:
Originally Posted by 911monty
However If you read Lubrizols ( major developers of Viscosity Modifiers)papers on the subject you will find that the 0W oils start with a 10 or less viscosity base stock, then through the use of long chain polymeric modifiers increase the viscosity to 30W 0r 40W.
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This is true with conventional oil, but synthetic base oils are inherently multi-grade and don't need friction modifiers (
link to reference)
Bottom line is look at the back of the bottle for the Porsche A40 spec. If it's there, you are good to go, otherwise use at your own risk. Note that formulations change all the time, so oils previously having the Porsche A40 rating may no longer be approved. For example, the Mobil1 15W50 oil which was Porsche A40 rated a couple months ago is no longer approved in favor of the new 5W50 oil. There are no 10W40 oils that are on the Porsche approved list.