ok. I'm really confused on oil #s...

[MattBrew]

can someone straighten me out on what exactly the xxW-xx mean on oils?

ASSuming no recommendation was givin by a manufacturer, how would one know what's best to run?

example; what is the difference between Mobil1 10w-30 and 5w-30?

 

[y_p_w]

quote:

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Originally posted by MattBrew:
can someone straighten me out on what exactly the xxW-xx mean on oils?

ASSuming no recommendation was givin by a manufacturer, how would one know what's best to run?

example; what is the difference between Mobil1 10w-30 and 5w-30?

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The W number corresponds to the winter viscosity. Each rating corresponds to two low temperature cold weather viscosity limits at sub-freezing temperatures 5°C apart. For 5W, that's cold cranking viscosity at -30°C and cold pumping viscosity at -35°C. The higher number corresponds to a viscosity range at "operating temperature" of 100°C. Certain things can be counterintuitive. For instance, there is such a thing as 20W-20 oil.

http://www.infineum.com/information/api-viscosity-2004.html

As for Mobil 1 5W-30 vs 10W-30, the answers are way too numerous depending on conditions. It gets really complicated since the 5W-30 "typical properties" have been changed such that their 5W-30 is quite a bit thicker at 100°C than the 10W-30. Fuel economy concerns make it really complicated. While their 5W-30 is more viscous, its HTHS viscosity is lower.

 

[Eddie]

To keep it simple for people like me. W means winter or cold and no W means summer or warm. SO a 5W oil flows better than 10W when cold. The high number, be it 20 or 30 or 50 means that a hier number will be thicker at high tempertures. so a top number of 50 is thicker than a 20. One should follow the car manufactures reomdation for which oil to use based on the tempature where you live.