“In most cases, you need to follow whatever viscosity is recommended by the automaker; you can find this information in the owner’s manual. Generally speaking, 10W-40 or 5W-30 are two of the best choices for summer, but you may also want to ask a mechanic to see what they say.
Motor oil viscosity, or the number you see on the label, such as 10W-30, is the most important number when it comes to your motor oil in the summer. The higher the second number, the better it’s going to work during summer heat.