5W/30 vs 10W/30

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1,815
Location
South Dakota
Am I correct in assuming that a 5W/30 wt. oil is the same as a 10w/30 when used during the summer? Aren't both a 30 wt. during summer temps? Isn't the difference during the winter when temps are lower and the 5W/30 flows easier?
 
Messages
6,902
Location
Louisiana
Yes, kinda. Many times a 5W30 and 10W30 will actually have slightly different warm weather variations within grade (ie thick vs. thin 30 weight).
 
Messages
1,577
Location
Surrey, BC
0W30, 5W30, and 10W30 will all flow the same (to the extent allowed within the range of "30" viscosity) when hot. The difference is in the cold flow. Note that by "cold" I mean startup temperature, and "hot" is operating engine temperature (~100 C). 5W30 will flow better cold than 10W30 all year, not just in the summer, but it would be more noticeable in the winter. Even in the summer, your engine is far below 100C at startup.
 
Messages
36,461
Location
ME
Look at some product data specs at 40'C which is over 100'F. The 5w30 is still thinner than the 10w30. The delta is of course less than you'd find at 0'C or less. Vilan nails it.
 
Messages
13,132
Location
By Detroit
Some brands will use more of a a better base oil in the 5w30 to compensate for the thinner base oil. For example, I recall Durablend had a lot more Group 1 base oil in the 10w30 than in the 5w30 according to the MSDS's.
 
Messages
190
Location
Cincinnati, OH
If you look at the data sheets, you might be surprised. Most 5w30 oils have a higher viscosity index at 100 degrees C, than the 10w30 oils. I really like the 5w30 oils year round.
 
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