Oil grades

[walter]

I was looking in my manual and saw the rec a 10-40 for temps of 0-65 and a 15-40 to 85. Why is the 10 40 not good above 65 when other 40 weights go higher? I am using Castrol Edge synthetic

[sprkn_ranger]

When looking at oil grade, the "W" stands for winter, so if you have a 10W-xx the oil is thinner in colder temps then the 15W-xx

Basically the first letter is the viscosity when the oil is cold, and the second number is the viscosity when the oil is at high temp (I believe the second temp is tested at 210 degrees)

Edited April 2, 2011 by sprkn_ranger

[white4d96]

You would be fine running the 10w40 in summer as well, it is just a recommendation for warm weather running.

FWIW when I didn't know any better I always ran 10w30 in my car, which requires 5w30. No oil-related issues there. If it was more than ten points or so I would say stick to it but 5 points really won't hurt.

[Julian@MotoCARR]

Great read on oil grades here.

Lots of racers use Blackstone labs for oil analysis to check for metal sediments, traces of coolant, etc.