Why exactly does 10w30 have a higher maximum operating temperature than 5w30 according to the owner's manual for our Volvo 850s? I understand how the 5w30 has a lower minimum operating temperature compared to the 10w30, but why would the 10w30 have a higher maximum temperature operating range compared to 5w30 if they are both 30 oils at operating temperature? I must be missing something here!

Lastly, I know this may sound stupid, but how exactly is that oil weight chart to be interpreted? From what I gather, it is saying don't run your car with 5w30 oil in it if the outside air temperature is above 68*F, don't run your car with 10w30 if the outside air temperature is below -4*F or above 104*F, etc. Is that correctly interpreted, or am I doing something wrong?

Also why is 10w30 shaded in red, and the other's aren't?

Thanks very much in advance!

 

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If they don't know, no one knows.

Yes, you are reading that chart right.

Personally, mine is at about 300K with a turbo so I run 10W40 or thicker in the summer and go with a 10W30 in Minnesota winters. But I do have a good starter, a big battery, MSD coil and keep it near stage 0 all the time.

 

The red line is recommended and will work for most applications/locations.