With $15 rebate offer from Quaker State on its Q Torque synthetic oil I went to AAP yesterday and bought 12 quarts 9buy 1 get 1 free) of 5W20 because that was all they had. My 2003 Toyota Echo engine specifies for 5W30. Since Toyota now uses 5W20 on their 2007 model cars, I wonder if I can use the 5W20 on my Echo? If not, will it be OK to mix it with 5W40 oil on 1:1 ratio to achieve final 5W30?