Quote:
Originally Posted by FRSRAVEN
The difference is how viscous they get at cold temperatures, and by cold, I mean below freezing.
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Yes, a 0W-20 is important when you take trips to the North Pole.
A 0W is tested at -35C and a 5W is tested at -30C.
ASTM D5293- Test Method for Apparent Viscosity of Engine Oils Between -5 and -35 C Using the Cold Crank Simulator This test method covers the laboratory determination of apparent viscosity of engine oils at temperatures between –5 and -35C and at high shear rates.
http://www.pqiamerica.com/coldcrank.htm
Using a
viscosity calculator like this one , you can get a general idea of how thick an oil is at a given temperature. Note that below 0C, it isn't as accurate as it is above 0C. You just need to go to the oil web sites to get the 40C and 100C from the product data sheets.
At operating temp., it's a pretty narrow range of viscosities (actual viscosity, not the grade listed on the bottle). A 20 grade starts at 5.6 cSt's and goes to 9.29 cSt's. But if you compare a 0W-20 vs. a 5W-20 at 0C (like Mobil1), the difference is more dramatic. 324.4 cSt's vs. 412.5 cSt's. It all comes down to what will give you the best fuel economy in government tests. Just do some reading on CAFE and CAFE credits. [ame="http://en.wikipedia.org/wiki/Corporate_Average_Fuel_Economy"]Corporate Average Fuel Economy - Wikipedia, the free encyclopedia[/ame]
It's really splitting hairs between a 5W-20 and 0W-20 though. Most new Subaru turbo owner's are trying to figure out what to run because so many people on the boards run 5W-40, but Subaru of America dropped 5W-40 from the owner's manual and 5W-40's have done very well in turbo's.
-Dennis