Is there any benefit/harm in mixing different weights of M1? My Tacoma manual call for a 5w-30 year round but it says that 10w-30 can be used in the summer. I'm due for an oil change and I was thinking about mixing in 2 qts of 5-w30 with 3 qts of 10w-30 ... to sort of cover all the bases. I live in the south where it's starting to get warm and it's real hot in the summer. Is mixing illogical?