5W-20 offers an increase in fuel economy and to this point have shown to be pretty good oils, plus they offer better low temperature performance.
5W-30 offers good cold weather performance and good high temperature protection to an extent but have not shown to be notably better than 5W-20 oils in applications where 5W-20 is reccomended.
10W-30 offers the best high temperature performance.
Question: What are the negative aspects of using a 5w20 oil?
Answer: 5w20 oil has less film and shear strength than a 5w30, 10w30 or a 0w30 motor oil. This can lead to increased engine wear under today's demanding heat and high-stress engine performance conditions.
Question: Don't I have to use a 5w20 oil to maintain my factory warranty if my manual recommends a 5w20 oil?
Answer: Absolutely not. Vehicle manufacturers recommend using motor oils meeting certain viscosity grades and American Petroleum Institute service requirements. Whether the motor oil is a 5w20, 5w30, 10w30 or 0w30 or even a synthetic vs. a petroleum-based oil will not affect warranty coverage. The manufacturer is required to cover all equipment failures it would normally cover as long as the oil meets API service requirements and specifications and was not the cause of the failure.
Bottom line, thicker = less engine wear, particularly in summer California where temperature in my area could reach up to +100F for weeks. This is why I always use 10w30 for summer and 5w30 for winter.
-2008 MDX Sport/Ent., Blk on Blk
-2014 IS 250 Blk on Blk
-2016 LSM V6 Touring Silver on Blk